MARINE VEHICLE TYPE- part 1

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type of marine vehicle



    Seagoing marine vehicles may be divided into   transport , including cargo, container and passenger ships and   nontransport   including  fi  shing vessels, service craft such as tugs and supply vessels, and warships. An overview of the wide range of ship types is given in   Figure. Each vessel type has a particular role to play and each will have a different set of design and operational conditions. This chapter provides a brief review of the main design and operational features of the principal types of marine vehicle.  

     Merchant ships 



    The development of merchant ship types has been 
dictated largely by the nature of the cargo and the 
trade routes. They can be classifi  ed accordingly with 
the major types being: 
  ●       general  cargo  ships  
  ●       container  ships  
  ●       tankers  
  ●       dry  bulk  carriers 
  ●       passenger  ships  
  ●       tugs. 


General  cargo  ships




    The industry distinguishes between   break bulk   cargo which is packed, loaded and stowed separately and   bulk cargo which is carried loose in bulk. The general cargo carrier (  Figure 2.2     ) is a fl  exible design of vessel which will go anywhere and carry a wide variety of cargo. The cargo may be break bulk or containers. Such vessels have several large clear open cargo-carrying spaces or holds. One or more decks may be present within the holds. These are known as  ’ tween decks and provide increased fl  exibility in loading and unloading, permit cargo segregation and improved stability. Access to the holds is by openings in the deck known as hatches.     Hatches are made as large as strength considerations permit in order to reduce the amount of horizontal movement of cargo within the ship. Typically the hatch width is about a third of the ship’s beam. Hatch covers are of various types. Pontoon hatches are quite common in ships of up to 10 000       dwt, for the upper deck and  ’ tween decks, each pontoon weighing up to 25 tonnes. They are opened and closed using a gantry or cranes. In large bulk carriers side rolling hatch covers are often fi  tted, opening and closing by movement in the transverse direction. Another type of cover is the folding design operated by hydraulics. The coamings of the upper or weather deck hatches are raised above the deck to reduce the risk of fl  ooding in heavy seas. They are liable to distort a little due to movement of the structure during loading and unloading of the ship. This must be allowed for in the design of the securing arrangements. Coamings can provide some compensation for the loss of hull strength due to the deck opening. 
    A  double  bottom  is  fi  tted along the ship’s length, divided into various tanks. These may be used for
fuel, lubricating oils, fresh water or ballast water. Fore and aft peak tanks are fi  tted and may be used to
carry ballast and to trim the ship. Deep tanks are often fitted and used to carry liquid cargoes or water ballast.
Water ballast tanks can be fi  lled when the ship is only partially loaded in order to provide a suffi  cient draught for stability, better weight distribution for longitudinal strength and better propeller immersion.
    Cranes and derricks are provided for cargo handling. Typically cranes have a lifting capacity of 10–25 tonnes with a reach of 10–20 m, but they can be much larger. General cargo ships can carry cranes or gantries with lifts of up to 150 tonnes. Above this, up to about 500 tonnes lift they are referred to as heavy lift ships.
    The machinery spaces are often well aft but there is usually one hold aft of the accommodation and
machinery space to improve the trim of the vessel when partially loaded. General cargo ships are generally
smaller than the ships devoted to the carriage of bulk cargoes. Typically their speeds range from 12 to 18 knots.  

    Refrigerated  cargo  ships  (Reefers)
 A refrigeration system provides low temperature holds for carrying perishable cargoes.

The holds are insulated to reduce heat transfer. The cargo may be carried frozen or chilled and holds are at different temperatures according to requirements. The possible effect of the low temperatures on surrounding structure must be considered. Refrigerated fruit is carried under modified atmosphere conditions. The cargo is maintained in a nitrogen-rich environment in order to slow the ripening process. The costs of keeping the cargo refrigerated, and the nature of the cargo, make a shorter journey time desirable and economic and these vessels are usually faster than general cargo ships with speeds up to 22 knots. Up to 12 passengers are carried on some, this number being the maximum permitted without the need to meet full passenger ship regulations.  

   Container  ships 

    Container ships are a good example of an integrated approach to the problem of transporting goods.

 Once goods are placed in the container at a factory or depot, they can be carried by road, rail or sea, being transferred from one to another at road or rail depots or a port. The container need not be opened until it reaches its destination. This makes the operation more secure. The maritime interest is primarily in the ports and ships but any element of the overall system may impose restrictions on what can be done. Height of container is likely to be dictated by the tunnels and bridges involved in land transport. Weight is likely to be dictated by the wheel loadings of lorries. The handling arrangements at the main terminals and ports are specially designed to handle the containers quickly and accurately. The larger container ships use dedicated

container ports and tend not to have their own cargo handling gantries.  The containers themselves are simply reusable boxes made of steel or aluminium. They come in a range of types and sizes. Details can be obtained from the web site of one of the operators. Nominal dimensions are lengths  of  20,  40  and  45   ft,  width  of  8  ft  and  height 8.5 or 9.5  ft. Internal volumes and weight of goods that can be carried vary with the material. For a 20  ft general-purpose steel container the internal capacity is about  33 m3  , weight empty is about 2.3 tonnef and the maximum payload is about 21.7 ton. Aluminium containers will have about the same volume, weigh less and be able to carry a larger payload. They are used for most general cargoes and liquid carrying.     The cargo-carrying section of the ship is divided into several holds with the containers racked in special frameworks and stacked one upon the other within the hold space. Containers may also be stacked on hatch covers and secured by special lashings. Some modern ships dispense with the hatch covers, pumps

dealing with any water that enters the holds. Each container must be of known all up weight and stowage arrangements must ensure the ship’s stability is adequate as well as meeting the offl  oading schedule if more than one port is involved. The ship’s deadweight will determine the total number of containers carried.   Cargo holds are separated by a deep web-framed structure to provide the ship with transverse strength. The structure outboard of the container holds is a box-like arrangement of wing tanks providing longitudinal and torsional strength. The wing tanks may be used for water ballast and can be used to counter the heeling of the ship when discharging containers. A double bottom is fi  tted which adds to the longitudinal strength and provides additional ballast space. Accommodation and machinery spaces are usually located aft leaving the maximum length of full-bodied ship for container stowage. The overall capacity of a container ship is expressed in terms of the number of standard 20 ft units it can carry, that is, the number of   twenty-foot equivalent units  (TEU). Thus a 40-foot container is classed as 2 TEU.   The container ship is one application where the size of ship seems to be ever increasing to take advantage of the economies of scale. By the turn of the century 6000 TEU ships had become the standard for the main trade routes, and some 80 ships of 8000 TEU were on order plus some of 9200 TEU. Concept work was underway for ships of 14 000 TEU size. Container ships tend to be faster than most general cargo ships, with speeds up to 30 knots. The larger ships

can use only the largest ports. Since these are fi  tted out to unload and load containers the ship itself does not

need such handling gear. Smaller ships are used on routes for which the large ships would be uneconomic, and to distribute containers from the large ports to smaller ports. That is, they can be used as feeder ships. Since the smaller ports may not have suitable handling gear the ships can load and offl  oad their own cargos.     Some containers are refrigerated. They may have their own independent cooling plant or be supplied with cooled air from the ship’s refrigeration system. Because of the insulation required refrigerated containers have less usable volume. Temperatures would be maintained at about    27°C and for a freezer unit about    60°C. They may be carried on general cargo ships or on dedicated refrigerated container ships. One such dedicated vessel is a 21 knot, 30 560 dwt ship of 2046 TEU capacity. The ship has six holds of which five are open. The hatchcover-less design enables the cell structure, in which the containers are stowed, to be continued above deck level giving greater security to the upper containers. Another advantage of the open hold is the easier dissipation of heat from the concentration of reefer boxes.

   Barge carriers are a variant of the container ship.

Standard barges are carried into which the cargo has been previously loaded. The barges, once unloaded, are towed away by tugs and return cargo barges are loaded. Minimal or even no port facilities are required and the system is particularly suited to countries with extensive inland waterways.

 Ref : Eyres, D.J. (2007) Ship Construction. Butterworth-Heinemann, Oxford, UK. [Section 2.2.4]

Rawson K.J. and Tupper E.C. (2001) Basic Ship Theory. 5th Edition, Combined Volume. 

Butterworth-Heinemann, Oxford, UK. [Sections 2.2.9, 2.4]

Tupper, E.C. (2004) Introduction to Naval Architecture. Butterworth-Heinemann, Oxford, UK.

[Sections 2.2.1–2.2.3, 2.2.5–2.2.8, 2.3, 2.5]

Maritime engineering reference book

TEORI BAJA

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Post By Ruth

Jenis baja dapat dibedakan menjadi :

1. Baja karbon
2. Baja paduan rendah berkekuatan tinggi
3. Baja paduan

Baja Karbon
Merupakan baja yang mengandung unsur bukan besi dengan persentase sebagai berikut:

• karbon 1.7%
• mangan 1.65%
• silikon 0.6%
• tembaga 0.6%

Karbon dan mangan adalah unsur utama yang dapat menaikkan kekuatan besi murni.Penambahan persentase karbon mengakibatkan peningkatan tegangan leleh tetapi mengurangi ductility sehingga baja sukar dilas.
Yang temasuk baja karbon disini adalah :

• baja karbon rendah : kandungan karbon kurang dari 0.15%
• baja karbon lunak : 0.15 - 0.29%
• baja kkarbon sedang : 0.30 - 0.59%
• baja karbon tinggi : 0.6-1.7%

Kurva Tegangan Regangan

Baja Paduan Rendah Kekuatan Tinggi
Adalah baja yang tegangan lelehnya antara 40-70 ksi (275-480 Mpa) dengan titik leleh sama seperti baja karbon. Baja ini merupakan perpaduan dari unsur chrom, columbium, tembaga, mangan, molybdenum,nikel, fosfor,vanadium atau zirconium.Dengan memperhalus mikrostruktur yang terjadi selama pendinginan baja. Baja jenis ini dipakai pada kondisi penggilingan/penormalan (tanpa perlakuan panas).

Baja Paduan
Baja jenis ini tidak membutuhkan perlakuan panas setelah dilas, merupakan baja yang mengandung karbon maksimal sebesar 0.2% , dengan maksud untuk membatasi kekerasan mikrostruktur kasar (martensit) yang dapat terbentuk selam retak kea perlakuan panas/pengelasan sehingga bahaya retak kecil.

Ductility adalah jumlah regangan permanen (regangan yang melampaui batas proporsional sampai titik patah /yield point). Besarnya ductility/daktilitas diperoleh dari uji tarik dengan menentukan persentase perpanjangan -dengan membandingkan luas penampang lintang akhir dan semula-dari benda uji.
Ductility sangat penting karena memungkinkan terjadinya kelelahan setempat akibat tegangan yang besar, sehingga distribusi tegangan berubah.

Fire Fighting Equipment

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ref: introduction marine engineering

Fire fighting equipment

Portable extinguishers

There are four principal types of portable extinguisher usually found on board ship. These are the soda-acid, foam, dry powder and carbon dioxide extinguishers.

Soda-acid extinguisher 
The container of this extinguisher holds a sodium bicarbonate solution. The screw-on cap contains a plunger mechanism covered by a safety
guard.  When the plunger is struck the glass phial is broken and the acid and sodium bicarbonate mix. The resulting chemical reaction produces carbon dioxide gas which pressurises the space above the liquid forcing it out through the internal pipe to the nozzle. This extinguisher is used for Class A fires and will be found in
accommodation areas.

Foam extinguisher—chemical

The main container is filled with sodium bicarbonate solution and a long inner polythene container is filled with aluminium sulphate . The inner container is sealed by a cap held in place by a plunger. When the plunger is unlocked by turning it, the cap is released.The extinguisher is then inverted for the two liquids to mix. Carbon
dioxide is produced by the reaction which pressurises the container andforces out the foam.

Foam extinguisher—mechanical

The outer container in this case is filled with water. The central container holds a carbon dioxide charge and a foam solution . A plunger mechanism with a safety guard is located above the central container. When the plunger is depressed the carbon dioxide is released and the foam solution and water mix. They are then forced out through a special nozzle which creates the mechanical foam. This extinguisher has an internal pipe and is operated upright. Foam extinguishers are used on Class B fires and will be located in the vicinity of flammable liquids.
A very strong container is used to store liquid carbon dioxide under pressure . A central tube provides the outlet passage for the carbon dioxide which is released either by a plunger bursting a disc or a valve operated by a trigger. The liquid changes to a gas as it leaves the extinguisher and passes through a swivel pipe or hose to a discharge horn. Carbon dioxide extinguishers are mainly used on Class B and C fires and will be found in the machinery space, particularly near electrical equipment. The carbon dioxide extinguisher is not permitted in the accommodation since, in a confined space, it could be lethal.

Dry powder extinguishers

The outer container contains sodium bicarbonate powder. A capsule of carbon dioxide gas is located beneath a plunger mechanism in the central cap. On depressing the plunger the carbon dioxide gas forces the powder up a discharge tube and out of the discharge nozzle. The dry powder extinguisher can be used on all classes of fire but it has no cooling effect. It is usually located near electrical equipment in the machinery space and elsewhere on the ship.

Maintenance and testing

All portable extinguishers are pressure vessels and must therefore be regularly checked. The soda-acid and foam extinguisher containers are initially tested to 25 bar for five minutes and thereafter at four-yearly intervals to 20 bar.
The carbon dioxide extinguisher is tested to 207 bar initially every 10 years and after two such tests, every five years. The dry powder extinguisher is tested to 35 bar once every four years. Most extinguishers should be tested by discharge over a period of one to five years, depending on the extinguisher type, e.g. soda-acid and dry powder types 20% discharged'per year, foam types 50% discharged per year. Carbon dioxide extinguishers should be weighed every six months to check' for leakage. Where practicable the operating mechanisms of portable extinguishers should be examined every three months. Any plunger should be checked for free movement, vent holes should be clear and cap threads lightly greased. Most extinguishers with screw-on caps have a number of holes in the threaded region. These are provided to release pressure before the cap is taken off: they should be checked to be clear.

FIRE FIGHTING AND SAFETY ON Ship - Part two

lovelymimiko@blogspot.com
ref: Introduction Marine Engineering

Detection

The use of fire detectors is increasing, particularly with the tendency to reduced manning and unmanned machinery spaces. A fire, if detected quickly, can be fought and brought under control with a minimum of
damage. The main function of a fire detector is therefore to detect a fire as quickly as possible; it must also be reliable and require a minimum of attention. An important requirement is that it is not set off by any of the
normal occurrences in the protected space, that is it must be appropriately sensitive to its surroundings. Three phenomena associated with fire are used to provide alarms: these are smoke, flames and heat, The smoke detector makes use of two ionisation chambers, one open to the atmosphere and one closed (Figure 13.1). The fine particles or aerosols given off by a fire alter the resistance in the open ionisation chamber, resulting in the operation of a cold cathode gas-filled valve. The alarm sounds on the operation of the valve to give warning of a fire. Smoke detectors are used in machinery spaces, accommodation areas and cargo holds.
Flames, as opposed to smoke, are often the main result of gas and liquid fires and flame detectors are used to protect against such hazards. Flames give off ultra-violet and infra-red radiation and detectors are available to respond to either.Flame detectors are used near to fuel handling equipment in the machinery spaces and also at boiler fronts.

Smoke Detector

FIRE FIGHTING AND SAFETY ON SHIP- Part 1

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Ref: Introduction marine engineering

Fire is a constant hazard at sea. It results in more total losses of ships than any other form of casualty. Almost all fires are the result of negligence or carelessness. Combustion occurs when the gases or vapours given off by a substance are ignited: it is the gas given off that burns, not the substance. The temperature of the substance at which it gives off enough gas to continue burning is known as the 'flash point'.

Fire is the result of a combination of three factors:
1. A substance that will burn.
2. An ignition source.
3. A supply of oxygen, usually from the air.

These three factors are often considered as the sides of the fire triangle. Removing any one or more of these sides will break the triangle and result in the fire being put out. The complete absence of one of the three
will ensure that a fire never starts. Fires are classified according to the types of material which are acting
as fuel. These classifications are also used for extinguishers and it is essential to use the correct classification of extinguisher for a fire, to avoid spreading the fire or creating additional hazards. The classifications use the letters A, B, C, D and E.
Class A Fires burning wood, glass fibre, upholstery and furnishings.
Class B Fires burning liquids such as lubricating oil and fuels.
Class C Fires burning gas fuels such as liquefied petroleum gas.
Class D Fires burning combustible metals such as magnesium and aluminium.
Class E Fires burning any of the above materials together with high voltage electricity.
Many fire extinguishers will have multiple classifications such as A, Band C.

Fire fighting at sea may be considered in three distinct stages, detection—locating the fire; alarm—informing the rest of the ship; and control—bringing to bear the means of extinguishing the fire.

ENGINE COOLING PROCESS

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Ref : Introduction marine engineering


Engine cooling process of engine divide into:

1. Fresh water cooling system
2. Sea water cooling system

Cooling of engines is achieved by circulating a cooling liquid around internal passages within the engine. The cooling liquid is thus heated up and is in turn cooled by a sea water circulated cooler. Without adequate
cooling certain parts of the engine which are exposed to very high temperatures, as a result of burning fuel, would soon fail. Cooling enables the engine metals to retain their mechanical properties. The usual coolant used is fresh water: sea water is not used directly as a coolant because of its corrosive action. Lubricating oil is sometimes used for piston cooling since leaks into the crankcase would not cause problems. As a result of its lower specific heat however about twice the quantity of oil compared to water would be required.

Fresh water cooling system

A water cooling system for a slow-speed diesei engine is shown in Figure 2.18. It is divided into two separate systems: one for cooling the cylinder jackets, cylinder heads and turbo-blowers; the other for piston cooling.

The cylinder jacket cooling water after leaving the engine passes to a sea-water-circulated cooler and then into the jacket-water circulating pumps. It is then pumped around the cylinder jackets, cylinder heads
and turbo-blowers. A header tank allows for  expansion and water make-up in the system. Vents are led from the engine to the header tank for the release of air from the cooling water. A heater in the circuit facilitates warming of the engine prior to starting by circulating hot water. The piston cooling system employs similar components, except that a
drain tank is used instead of a header tank and the vents are then led to high points in the machinery space. A separate piston cooling system is used to limit any contamination from piston cooling glands to the piston cooling system only.


Sea water cooling system

The various cooling liquids which circulate the engine are themselves cooled by sea water. The usual arrangement uses individual coolers for lubricating oil, jacket water, and the piston cooling system, each cooler being circulated by sea water. Some modern ships use what is known as a 'central cooling system' with only one large sea-water-circulated cooler. This cools a supply of fresh water, which then circulates to the32 other Individual coolers. With less equipment in contact with sea water the corrosion problems are much reduced in this system. A sea water cooling system is shown in Figure 2.19. From the sea suction one of a pair of sea-water circulating pumps provides sea water which circulates the lubricating oil cooler, the jacket water cooler and the piston water cooler before discharging overboard. Another branch of the sea water main provides sea water to directly cool the charge air (for a direct-drive two-stroke diesel). One arrangement of a central cooling system is shown in Figure 2.20. The sea water circuit is made up of high and low suctions, usually on either side of the machinery space, suction strainers and several sea water pumps. The sea water is circulated through the central coolers and then discharged overboard. A low-temperature and high-temperature circuit exist in the fresh water system. The fresh water in the high-temperature circuit circulates the main engine and may, if required, be used as a heating medium for an evaporator. The
low-temperature circuit circulates the main engine air coolers, the lubricating oil coolers and all other heat exchangers. A regulating valve controls the mixing of water between the high-temperature and
low-temperature circuits. A temperature sensor provides a signal to the control unit which operates the regulating valve to maintain the desired temperature setting. A temperature sensor is also used in a similar
control circuit to operate the regulating valve which controls the bypassing of the central coolers. It is also possible, with appropriate control equipment, to vary the quantity of sea water circulated by the pumps to almost precisely meet the cooler requirements.

FUEL OIL SYSTEM OF DIESEL ENGINE

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The fuel oil system for a diesel engine can be considered in two parts—the fuel supply and the fuel injection systems. Fuel supply deals with the provision of fuel oil suitable for use by the injection system.

Fuel oil supply for a two-stroke diesel

A slow-speed two-stroke diesel is usually arranged to operate continuously on heavy fuel and have available a diesel oil supply for manoeuvring conditions. In the system shown in Figure 2.11, the oil is stored in tanks in the double bottom from which it is pumped to a settling tank and heated. After passing through centrifuges the cleaned, heated oil is pumped to a daily service tank. From the daily service tank the oil flows through a three-way valve to a mixing tank. A flow meter is fitted into the system to indicate fuel consumption. Booster pumps are used to pump the oil through heaters and a viscosity regulator to the engine-driven fuel
pumps. The fuel pumps will discharge high-pressure fuel to their respective injectors. The viscosity regulator controls the fuel oil temperature in order to provide the correct viscosity for combustion. A pressure regulating valve ensures a constant-pressure supply to the engine-driven pumps, and a pre-warming bypass is used to heat up the fuel before starting the engine. A diesel oil daily service tank may be installed and is connected
to the system via a three-way valve. The engine can be started up and manoeuvred on diesel oil or even a blend of diesel and heavy fuel oil. The mixing tank is used to collect recirculated oil and also acts as a
buffer or reserve tank as it will supply fuel when the daily service tank is empty. The system includes various safety devices such as low-level alarms and remotely operated tank outlet valves which can be closed in the
event of a fire.

Comparison of two-stroke and four-stroke cycles

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The main difference between the two cycles is the power developed. The
two-stroke cycle engine, with one working or power stroke every
revolution, will, theoretically, develop twice the power of a four-stroke
engine of the same swept volume. Inefficient scavenging however and
other losses, reduce the power advantage to about 1.8. For a particular
engine power the two-stroke engine will be considerably lighter—an
important consideration for ships. Nor does the two-stroke engine
require the complicated valve operating mechanism of the four-stroke.
The four-stroke engine however can operate efficiently at high speeds
which offsets its power disadvantage; it also consumes less lubricating
oil.

Each type of engine has its applications which on board ship have
resulted in the slow speed (i.e. 80— 100 rev/min) main propulsion diesel
operating on the two-stroke cycle. At this low speed the engine requires
no reduction gearbox between it and the propeller. The four-stroke
engine (usually rotating at medium speed, between 250 and 750 rev/
min) is used for auxiliaries such as alternators and sometimes for main
propulsion with a gearbox to provide a propeller speed of between 80
and 100 rev/min.

Reference : Introduction marine engineering

TIGA (3) LANGKAH TAMPIL CANTIK

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3 Langkah Tampil Cantik Di
Segala Usia

Setiap fase usia punya keistimewaan tersendiri. Tentunya… sebagai kaum wanita ingin selalu tampil cantik dan menawan berapapun usianya. Untuk mendapatkan kecantikan abadi tersebut, harus dilakukan perawat secara
tepat. Karena itu, lakukan perawatan yang sesuai untuk setiap tahapan usia.

CANTIK DI USIA 20 – AN
Puncak perkembangan kulit terjadi di usia 20 – an. Pada masa ini, semua komponen kulit seperti epiderma, kolagen, elastin dan pembuluh darah berkembang secara maksimal. Sehingga tekstur kulit terlihat berwarna
kemerahan segar. Masalah utama yang menghantui pada masa ini, biasanya hanya seputar kulit
berminyak dan berjerawat yang disebabkan oleh faktor hormonal atau perawatan yang kurang tepat. Selain kedua hal itu hampir tidak ada problem yang patut dicemaskan.

Perawatan Harian
 Lakukan perawatan ringan dan teratur setiap hari, selalu
membersihkan wajah dengan pembersih sebelum tidur. Agar
wajah bisa “bernapas” dengan nyaman. Pilih pembersih dan
penyegar yang tepat, sesuai dengan kondisi kulit (berminyak,
kering, sensitive, normal ataupun kombinasi). Karena tiap kulit
yang berbeda, memerlukan perawatn yang berbeda pula.
Oleskan setiap malam eye gel sebelum tidur.
 Gunakan pelembap yang mengandung SPF, minimal 15 atau
lebih terutama jika Anda termasuk wanita aktif yang sering
berada di luar ruangan dalam waktu lama. Oleskan 15-20 menit
sebelum ke luar ruangan, agar meresap sempurna.
 Masukkan juga buah – buahan, sayur mayur dan air putih dalam
menu makan Anda. Kanduangan serat serta vitamin dalam buah dan sayur membantu proses regenerasi kulit secara alami, sementara air putih mampu mempercepat pengeluaran racun dan lemak tak berguna
dalam tubuh yang menjadi penyebab jerawat.

Perawatan Mingguan
Melakukan facial, peeling, dan pakai masker secara berkala merupakan perawatan tambahan yang dapat dilakukan sebagai tindakan pencegahan penuaan dini.
 Lakukan facial dengan teknik pemijatan secara tepat, karena
apabila salah pijat, bisa memicu timbulnya kerutan di wajah.
Anda pun bisa melakukannya sendiri, asalkan Anda tahu
caranya.
 Selain facial, lakukan juga peeling. Peeling berfungsi untuk
mengangkat sel kulit mati. Berapa sering Anda melakukan
peeling? Hal tersebut tergantung bagaimana kondisi kulit Anda.
Untuk kulit kering dan sensitif antara 7 - 14 hari sekali, kulit
normal 5 hari sekali dan kulit berminyak 3 - 5 hari sekali.
Pastikan tidak ada luka atau infeksi pada wajah saat melakukan
pengelupasan dan jangan melakukan peeling terlalu sering agar
kulit memiliki kesempatan regenerasi.
 Maker berfungsi untuk menyegarkan kulit dan
mempercantiknya. Banyak pilihan masker yang bisa Anda pakai.
Baik yang keluaran pabrik atau keluaran dapur Anda, membuat
sendiri maksudnya  lebih murah, mudah, dan yang pasti aman. Yang penting adalah memperhatikan manfaat dan kandungan bahan pembuatnya.

Make Up
Pemilihan kosmetik pada usia ini dapat lebih bervariasi, berbagai
warna riasan dapat dicoba. Anda bisa mencoba berbagai macam warna
dan gaya make-up untuk meng-xplor kecantikan. Mumpung masih
muda 
Jika tidak diperlukan hindari penggunaan foundation dan concealer
terlalu sering. Jika memang diperlukan, gunakan yang berbahan dasar air (water based), agar terasa lebih ringan. Penggunaan foundation
menyebabkan pori–pori tersumbat, dan kalo pori-pori tersumbat akan
menimbulkan komedo dan jerawat. Sebagai alternatif, cukup oleskan
pelembap ringan dan bedak tabur (ditekan-tekan dengan mengunakan
puff). Pilih warna–warna transparan untuk bedaknya, agar wajah
terlihat lebih segar dan bersinar.

MENARIK DI USIA 30-AN
Mulai usia 30, tanda–tanda penuaan sudah mulai terjadi. Proses
pengelupasan kulit mati mulai melambat, kolagen dan elastin berkurang dan
mulai terlihat kantong mata. Selain itu warna kulit mulai tidak merata, kulit
terasa lebih kering serta timbul garis–garis halus pada ujung mata dan bibir,
Ini dikarenakan penyebab utamanya adalah perubahan hormon.
Memasuki usia ini, Anda harus lebih selektif dalam memilih produk perawatan
dan riasan wajah. Lakukanlah semua perawatan harian yang telah Anda jalani
dengan lebih intensif lagi. Ganti produk ringan yang biasa Anda pakai, dengan
jenis yang mempunyai kekuatan lebih yang berguna untuk menghindari
penuaan dini.
Perawatan Harian
 Jangan lupa selalu membersihkan wajah setelah beraktifitas dan
sebelum tidur. Pilih penyegar yang tidak mengandung alcohol.
Karena alcohol akan membuat kulit semakin kering dan kulit
kering mempercepat timbulnya keriput.
 Gunakan pelembap yang berbeda untuk siang dan malam secara
teratur (pelembap siang yang mengandung tabir surya dan
pelembap malam yang mengandung anti–aging untuk
membantu regenerasi kulit di malam hari).
 Oleskan krim mata untuk melembapkan daerah kantong mata
agar tidak gampang berkerut atau kendur.Perawatan Mingguan
 Lakukan perawat mingguan seperti pada usia 20-an. Yaitu facial,
peeling dan masker. Yang membedakan hanyalah pemilihan
bahan yang digunakan untuk peeling dan maskernya. Peeling
untuk menipiskan noda-noda kecoklatan akibat rusaknya
melanin karena sinar UV dan masker agar regenerasi kulit
berlangsung optimal atau gunakan masker yang berfungsi untuk
mengencangkan dan menjaga kelembaban kulit. Anda pun dapat
mencoba membuat ramuan untuk peeling dan masker sendiri
koq… so, lebih murah dan aman kan….
 Pilih satu olah raga favorit Anda dan lakukan secara teratur 2 –
3 kali seminggu.
Make Up
 Untuk riasan lakukan, trik koreksi wajah. Contoh: lakukan
koreksi untuk menyamarkan bentuk mata yang turun dengan
teknik khusus menggunakan eyeliner dan eyeshadow yang
tepat, untuk menyamarkan noda hitam atau kerutan halus dan
menutupi kantong mata yang mulai nampak, bubuhkan
concealer tipis–tipis.
 Selanjutnya bingkai bibir dengan pensil secara tipis–tipis guna
menyamarkan kerutan halus yang muncul disekitar bibir
kemudian oleskan lipstik secara merata di bibir. Warna-warna
muda atau pastel membuat Anda tampak lebih muda. Hindari
warna coklat, warna tua, dan warna-warna yang sudah
ketinggalan zaman.
 Perhatikan pemerah pipi Anda akan tampak lebih tua bila
mengoles pemerah pipi terlalu ke bawah. Temukan tulang pipi
Anda dan oleskan pemerah pipi di atasnya.
 Begitu usia mencapai 30 tahun ke atas, Anda harus mulai
berhati-hati dalam memakai alis mata. Hindari pemakaian yang
tebal.
 Untuk menyulap penampilan agar tampak 10 tahun lebih muda…
Caranya amat mudah. Sebelum ritual memulas wajah dengan
rangkaian kosmetik, basuhkan es batu pada wajah anda secara merata selama 10-15 menit, lalu keringkan dengan seksama
menggunakan handuk lembut. Setelahnya, baurkan moisturizer
berbahan dasar air.
Setelah moisturizer meresap dan kulit menjadi terlihat halus,
pilih foundation ringan berbentuk cair (liquid). Foundation cair
lebih tahan lama dan bisa membuat kerutan tersamar
sempurna. Lalu ber-make-up lah seperti biasa. Gunakan warna-
warna yang natural dan sedikit pinkish atau goldie untuk anda
yang berkulit agak gelap. Nah, anda jadi terlihat 10 tahun lebih
muda, kan?
 Pilih warna natural atau pastel agar tampak natural.
TIPS:
Lakukan beberapa hal untuk mempertahankan kecantikan kulit wajah dan
hindari kebiasan buruk yang dapat mempercepat kerusakan kulit seperti:
1. hindari merokok
2. hindari juga minum berkafein
3. jangan tidur terlalu malam
4. minum air putih, minimal 8 gelas per hari
5. perhatikan pula posisi tidur. Hindari posisi tidur yang miring dan
telungkup sepanjang malam.
Untuk mengetahui keteranagan lebih lengkap mengenai bagaimana cara facial
yang tepat, kandungan tiap produk kecantikan yang tepat sesuai kondisi kulit
(berminyak, kering, dan sebagainya), berbagai macam gaya make-up yang
bisa Anda coba, dan lebih dari 150 ramuan tradisional buatan Anda sendiri.

disadur : www.paketcantik.com

Bagaimana cara menentukan Jenis Kulit Kita: berminyak , normal atau keringkah?

lovelymimiko@blogspot.com

Tes Jenis Kulit Mu!
Temukan Kecantikan Kulit Sejati Mu

Pengetahuan tentang apa jenis kulit wajah Anda yang sebenarnya,merupakan satu dasar yang sangat penting dalam kecantikan.Kenapa hal tersebut penting?Hal ini memiliki peran yang sangat penting dan vital dalam perawatan kulitwajah, memilih produk perawatan kulit wajah, dan pemilihan make-up yang tepat.Sebagai contohnya, banyak produk pembersih wajah (susu pembersih) yang memiliki beragam variasi pilihan jenisnya. Ada yang untuk kulit berminyak, kering, normal, dan sebagainya. Setiap jenis pembersih yang berbeda
memiliki kandungan bahan pembuat yang berbeda pula. Kandungannya disesuaikan dengan bahan-bahan apa saja yang bekerja lebih efektif untuk jenis kulit tertentu. Misalnya, Pembersih wajah untuk kulit berminyak menggunakan formula yang bebas minyak (oil free). Nah… bayangkan, apa yang akan terjadi ketika orang
yang salah diagnosa dan menganggap memiliki kulit berminyak menggunakan pembersih yang seperti itu. Akibatnya… kulitnya akan semakin kering. Apakah Anda tahu tidak, kalo kulit kering menjadi salah satu pemicu timbulnya kerutan alias penuaan dini? Ih…. Gak mau kan?! Menjadi kelihatan cepat tua gara-gara salah memakai pembersih… Bukan hanya dalam hal perawatan wajah saja, memilih make-up pun harus
memperhatikan jenis kulit lo… pernahkah Anda melihat orang yang make-up- nya menggumpal-gumpak di wajah atau yang mengkilat, kelihat berminyak sekali. Sehingga orang tersebut tampak belepotan, tidak rapi, dan kelihatan jorok? Kemungkinan… orang tersebut salah memilih make-up. Entah itu untuk pelembabnya, alas bedak atau bahkan keduanya. Mungkin, kulitnya berminyak, lalu memakai krim pelembab dan alas bedak yang berbentuk compact/cake (padat). Padahal, kedua make-up (krim pelembab dan alas
bedak padat tersebut) masuk zona merah bagi kulit berminyak. Karena kedua bahan tersebut banyak mengandung minyak. Nah… itu baru dua “bencana” yang diakibatkan karena salah diagnosa. Contoh
yang saya sebutkan itu adalah contoh yang paling gampang. Dan masih buanyak lagi “bencana” yang bisa ditimbulkannya. Itu baru dari kesalah memilih produk kosmetik saja lo… belum tentang perawatan dan lain
sebaginya. Memang sih… ada sebagian orang yang merasa yakin memiliki kulit dengan suatu jenis tertentu. Karena ciri-ciri fisiknya sangat jelas, seperti kulitnya berminyak sekali, berarti kemungkinan dia memiliki jenis kulit yang berminyak. Tetapi apakah Anda sudah yakin benar? Lalu bagaimana kalo salah?
Masih binging?
Bagi yang masih bingung…. Ikuti saya! Dan bagi yang sudah yakin, gak ada salahnya kan… memastikannya lagi. Sekarang… coba lakukan tes kecil untuk mengetahui bagaimana jenis kulit Anda yang sebenarnya.
Anda siap??

 Pertama, basahi dulu wajah Anda dengan air,
 Diamkan selama 1 sampa 2 jam, tanpa menggunakan produk kecantikan apapun,
 Lanjutkan dengan menekannya pada bagian kening, hidung, dagu, dan pipi menggunakan tisu, n lihat hasilnya… 

Bila tidak ada berkas minyak di kulit, berarti Anda memiliki kulit wajah normal.

•  Bila permukaan wajah meninggalkan berkas berminyak, berarti Anda memiliki kulit wajah berminyak.
• Bila terdapat serpihan kulit yang terbawa tisu, berarti Anda memiliki kulit wajah kering. Perlu diingat, bila kulit tetap kering meski telah diberi pelembab, ada kemungkinan kulit mengalami peradangan atau infeksi.Lebih baik konsultasikan pada dokter spesialis kulit.

• Bila beberapa bagian kulit wajah di daerah T (kening, hidung, dan dagu) terdapat berkas minyak, berarti Anda memiliki kulit wajah kombinasi kering-berminyak.

Bagaimana dengan punya Anda? Semoga tes kecil tersebut bisa memberi pencerahan baru kepada Anda. Selamat mencoba dan temukan kecantikanmu dengan perawatan, produk, dan make-up yang tepat.

disadur : paketcantik.com

The Titanic's Steel test

In 1996, several samples of steel from the Titanic—a hull plate from the bow area and a plate from a major transverse bulkhead—were recovered from the wreck site and subjected to metallurgical testing by Prof. H.P. Leighly at the University of Missouri-Rolla, as well as at the laboratories of Bethlehem Steel and the National Institute of Standards and Technology. Chemical testing revealed a low residual nitrogen and manganese content, and higher levels of sulfur, phosphorus, and oxygen than would be permitted today in mild steel plates or stiffeners. This indicates that the steel was produced by the open-hearth rather than the Bessemer process, most likely in an acid-lined furnace; the steel is of a type known as semi-killed, that is, partially deoxidized before casting into ingots. (Other fragments of the Titanic's hull have yielded slightly different results, suggesting a degree of variability in the chemical and, hence, the mechanical properties of the steel used in the ship.)
Excess oxygen can form precipitates that can embrittle the steel, and will also raise transition temperatures. In the absence of sufficient manganese, sulfur reacts with the iron to form iron sulfide at the grain boundaries; it can also react with manganese, in either case creating paths of weakness for fractures. Sulfide particles under stress can nucleate microcracks, which further loading will cause to coalesce into larger cracks; in fact, this was found to have been the mode of failure in the shell plating of the Titanic. Phosphorus, even in small amounts, has been found to foster the initiation of fractures. Of course, much of this metallurgical information has only been learned in the years since the Titanic went down.
To determine the steel's mechanical properties, it was subjected to tensile testing, as well as the Charpy V-Notch Test, used to simulate rapid loading phenomena; the test used samples oriented both parallel and perpendicular to the original direction of the hull plate. The ductile-brittle transition temperature (using 20 lbs.-ft. for the test) was found to be 20°C in one direction and 30°C in the other, compared with —15°C for a reference sample of modern A 36 steel—and a water temperature of —2°C on the night the ship collided with the iceberg. The Titanic steel was also shown to have approximately one-third the impact strength of modern steel.
When the Titanic samples were also examined with a scanning electron microscope, the grain structure of the steel was found to be very large; this coarse structure made it easier for cracks to propagate. Rivet holes were cold-punched, a method no longer allowed (they must now be drilled), nor were they reamed to remove microcracks.
The steel grain size; the oxygen, sulfur, and phosphorus content of the steel; and the cold-punched, unreamed rivet holes were found to have contributed to the breakup of theTitanic, along with the steel's relatively low ductility at the freezing point of water. The shell plates showed signs of brittle fracture, though some plates demonstrated significant plasticity.
Of course, the science of metallurgy has advanced considerably since the Titanic's day, and William Garzke of Gibbs and Cox and his collaborators emphasized in their report that "the steel used in the Titanic was the best available in 1909-1914" when the ship was built. In fact, they add that when 39,000 tons of water entered the bow, "no modern ship, not even a welded one, could have withstood the forces that the Titanic experienced during her breakup.
By Henry Baumgartner

HOW DID the TITANIC sink?? Part 2

This article is based on a paper, "Titanic, The Anatomy of a Disaster, A Report from the Marine Forensic Panel,"presented at the 1997 annual meeting of the Society of Naval Architects and Marine Engineers, that documents the work of William H. Garzke, Jr. and David Wood, Gibbs & Cox, Inc.; David K. Brown, RCNC; Paul K. Matthias, Polaris Imaging; Dr. Roy Cullimore, University of Regina; David Livingstone, Harland & Wolff; Prof. H.P. Leighly, Jr., University of Missouri-Rolla; Dr. Timothy Foecke, National Institute of Standards and Technology; and Arthur Sandiford, Consultant. Eyewitness accounts are from various sources, including the official transcripts of the 1912 U.S. Senate investigation.
The Death of a Ship
At 2:17 a.m., according to the various investigations after the disaster, the Titanic began to go under, her lights blazing in the cold of the sub-Arctic night and with more than 1,500 people still on board. With a rumbling, crashing noise, the bow of the ship sank deeper into the water and the stern rose into the air.
Believing that the Titanic was invincible, many passengers were willing to board lifeboats only after the bow began to sink below the water's surface.
The stern section remained motionless and high out of the water for 30 seconds or more. The hull fracture was described as the sound of breaking chinaware, but as it continued, it was like a loud roar. A minute later, her lights flickered and then went out.
Then, at 2:20 a.m., the stern settled back into the water. Following a series of explosions, the submerged forward section began to pull away from the stern. As the forward section began its long descent, it drew the stern almost vertical again. Once this began, Titanic picked up speed as she sank below the surface of the pond-still waters of the North Atlantic. Some of the survivors on the stern stated that it was almost perpendicular as it slid silently and with hardly a ripple beneath the surface. William Garzke, staff naval architect at Gibbs & Cox, points out that, had the liner been elevated at 90 degrees, the huge boilers would have been ripped from their moorings, which was not the case. He suggests that the stern section likely rose from the surface to at least 20 degrees but not more than 35 degrees, as it filled with water or was dragged down by the bow section.
Chief Baker Charlie Joughin, who was at the ensign staff at the stern end, later testified that it was like riding an elevator down to the water. With the absence of suction forces, he was able to swim away without even wetting his hair, so swift was the stern's demise.
The failure of the main hull girder of the Titanic was the final phase of her sinking process. This began between 2:00 and 2:15 a.m., starting somewhere between stacks Nos. 2 and 4. The FEA results indicate that the plate failures might have started around the second expansion joint, or just behind it.
Stresses in the hull were increasing as the bow flooding continued and the stern rose from the water. Detailed examination of survivor testimony and underwater surveys has confirmed that the forward expansion joint was opened up while the ship was still on the surface, suggesting the significant stresses induced by the flooding of the forward part of the hull. An FEA review of the stresses in this area confirms that the nominal hull stresses were well above the material yield stress.
Most probably, significant stress developed in the way of the second expansion joint, between its root and the deck structure below it. As the flooding progressed aftward, the hull girder was strained beyond its design limitations, and the local stresses around this expansion joint soon reached the ultimate strength of the material. It is thought that, in the end, a critical structural failure in the hull or deck plates occurred in the area around the second expansion joint.

A stress analysis suggests that the Titanic's hull girder stresses exceeded the yield point of the steel.Once localized fracture began in the way of this joint, additional plate failures and associated fracturing likely radiated out from this joint, toward both port and starboard. The decks, however, with their finer grain structure, were most likely able to deform well into the plastic range of the material before failing in ductile tears. It is speculated, however, that the side shell plates suffered brittle fracture due to their coarser grain structure and manganese sulfide inclusions. This type of failure is evident on the wreck today.
Free field stresses, already at the yield point of the material, may have been increased by a factor of two to four in areas of structural discontinuities, such as large openings or those with small radii, or doubler plate edges. Fractures typically spread in random chaotic paths, following weaknesses in the plate and microcracks already present around rivet holes.
Assuming that the hull girder failed at the surface, then as Boiler Room No. 4 filled with water, the stern rose farther out of the water, resulting in some 76 meters of unsupported hull, which sharply increased the hull girder stresses, in turn accelerating the fracturing of the steel plates. The angle of trim grew to a maximum of 15 to 20 degrees, further increasing the stresses in the hull and deck plating near the aft expansion joint. The stresses continued to build in this area of the ship, where there were large openings for a main access, the machinery casing for the Reciprocating Engine Room, the uptakes and intakes for the boilers, the ash pit door on the port side of Boiler Room No. 1, and the turbine engine casing. As the hull girder continued to fail, the bow was first to begin its plunge toward the seabed.
As the bow and stern sections continued to separate, there were some local buckling failures in the inner bottom and bottom structure. This is what caused the stern section to settle back toward the water's surface as the decks began to fail and the side shell fractured into many small plate sections. The MSC/NASTRAN finite element analysis indicates that the stresses in the region of Boiler Room No. 1 and the Reciprocating Engine Room were elevated.
An additional stress analysis, based on classical beam theory, indicates that the hull girder stresses exceeded the yield point of the steel. When the bow and stern began to separate, the two main transverse bulkheads bounding Boiler Room No. 1 collapsed as they were compressed by the downward movement of the deck structures. The decks, in turn, failed because of the lack of bulkhead support.
When this happened, the unsupported length of the inner bottom suddenly grew to 165 feet, encompassing Boiler Rooms Nos. 1 and 2, as well as the Reciprocating Engine Room. This condition allowed deformation of the inner bottom structure to extend up further into the ship's machinery spaces, while the deck structure failures continued. It is believed that this compression of the hull girder brought about the failure of the side shell plates, and also freed equipment inside the ship, such as the boilers in Boiler Room No. 1, from its foundations.
It cannot be established with any certainty what happened to the ship during its descent to the seabed. However, what is now known is that once the Titanic disappeared below the ocean's surface, it broke into three pieces. The depth where these events occurred cannot be estimated with any precision. The buoyancy of the stern piece also appears to have resisted the downward pull of the bow. The extent of damage evident in the stern wreck implies that the bow section may have pulled the stern section quickly below the water's surface, resulting in structural implosions that caused significant damage. Structural failures ultimately led to the separation of the bow portion, followed by the third or double bottom piece. It is interesting to note that the bow section did not suffer damage similar to that in the stern section. This was likely due to the gradual flooding of the bow section, and its stability during the descent to the bottom. It rests upright on the bottom with little apparent damage directly attributable to impact with the seabed.
The analysis supports some witnesses' testimony that the ship likely began to fracture at the surface, and that the fracture was completed at some unknown depth below the water's surface. The resulting stress levels in the strength deck below the root of the second expansion joint (aft), and in the inner bottom structure directly below, were very high because of the unusual flooding occurring in the forward half of the ship. These patterns of stress support the argument that initial hull failure likely occurred at the surface. Additional work is being performed to investigate this further.
These findings mirror the testimony of Seaman Edward John Buley at the U.S. Senate hearings. Stating that as the bow continued to slip below the surface, "She went down as far as the after funnel, and then there was a little roar, as though the engines had rushed forward, and she snapped in two, and the bow part went down and the afterpart came up and stayed up five minutes before it went down ... It was horizontal at first, and then went down."
In response to what he meant by "snapped in two,"and how he knew this, Buley testified, "She parted in two ... Because we could see the afterpart afloat, and there was no forepart to it. I think she must have parted where the bunkers were. She parted at the last, because the afterpart of her settled out of the water horizontally after the other part went down. First of all, you could see her propellers and everything. Her rudder was clear out of the water. You could hear the rush of the machinery, and she parted in two, and the afterpart settled down again, and we thought the afterpart would float altogether. She uprighted herself for about five minutes, and then tipped over and disappeared ... You could see she went in two, because we were quite near to her and could see her quite plainly."
RMS Titanic, the largest ship of its day, was built in Belfast, Ireland, and was said to be "unsinkable,"a belief so strong that it was to have tragic consequences. Having confidence in the ship's "unsinkability,"many passengers chose to remain on board. The first lifeboats to leave were only half, or one-third full.
The fallacy of the claim itself became tragically apparent during the ship's maiden voyage. Just three hours after it collided with an iceberg, the majestic Titanic vanished beneath the cold waters of the North Atlantic. This ill-founded confidence led to the ignoring of at least 14 warnings of hazardous ice fields, six of which were received on the day of the disaster.
Equipped with only 20 lifeboats, the Titanic went down with the loss of 1,523 passengers and crew. This incredible disaster led to a number of investigations in Great Britain and the United States that resulted in sweeping changes in maritime safety law and ship construction.
The demise of the mighty Titanic was swift, sure, and terrible. Whatever could have gone wrong, did. The engineering marvel that heralded the beginning of the age of technology also displayed, all too clearly, its vulnerability and limits—as well as the need for prudence and safety.
"The analyses, and future analyses we hope to make employing both MSC/NASTRAN and MSC/DYTRAN, help us make critical design decisions about future marine structural features, such as deck openings and expansions joints."Wood said.
"Today, we're changing the way we design ships. In the past, nominal load conditions were averaged. Today, we design for the ultimate stress levels and strength,"says Robert Sielski, senior staff engineer at Gibbs & Cox. "MSC/NASTRAN helps us evaluate and design for increased survivability."

lovelymimiko@blogspot.com

HOW DID THE TITANIC SINK? part 1

By Dan Deitz, Executive Editor of MEMAGAZINE
This article is based on a paper, "Titanic, The Anatomy of a Disaster, A Report from the Marine Forensic Panel,"presented at the 1997 annual meeting of the Society of Naval Architects and Marine Engineers, that documents the work of William H. Garzke, Jr. and David Wood, Gibbs & Cox, Inc.; David K. Brown, RCNC; Paul K. Matthias, Polaris Imaging; Dr. Roy Cullimore, University of Regina; David Livingstone, Harland & Wolff; Prof. H.P. Leighly, Jr., University of Missouri-Rolla; Dr. Timothy Foecke, National Institute of Standards and Technology; and Arthur Sandiford, Consultant. Eyewitness accounts are from various sources, including the official transcripts of the 1912 U.S. Senate investigation.

When our boat had rowed about half a mile from the vessel, the Titanic—which was illuminated from stem to stern—was perfectly stationary, like some fantastic piece of stage scenery,"recalled Pierre Marechal, a French aviator and a surviving first-class passenger of the ill-fated liner. "Presently, the gigantic ship began to sink by the bows ... suddenly the lights went out, and an immense clamor filled the air. Little by little, the Titanic settled down ... and sank without noise ... In the final spasm the stern of the leviathan stood in the air and then the vessel finally disappeared."
British and U.S. investigations of the Titanic tragedy have resulted in greater lifeboat capacity, improved subdivision of ships, and the creation of an ice patrol.
Elmer Z. Taylor, who watched from Lifeboat No. 5, close enough to the Titanic to observe its final demise, would later write, "The cracking sound, quite audible a quarter of a mile away, was due, in my opinion, to tearing of the ship's plates apart, or that part of the hull below the expansion joints, thus breaking the back at a point almost midway the length of the ship."
"At that time the band was playing a ragtime tune, "remembered Harold Sydney Bride, the surviving wireless operator of the Titanic. "I saw a collapsible boat on deck ... I went to help when a big wave swept it off, carrying me with it. The boat was overturned and I was beneath it, but I managed to get clear. I swam with all my might and I suppose I was 150 feet away when the Titanic, with her aft quarter sticking straight up, began to settle."
"The orchestra belonging to the first cabin assembled on deck as the liner was going down and played 'Nearer My God to Thee.' By that time,"as Miss C. Bounnell, first-class survivor, relived the night, "most of the lifeboats were some distance away and only a faint sound of the strains of the hymn could be heard. As we pulled away from the ship, we noticed that she was hog-backed, showing she was already breaking in two."
Four survivors with firsthand knowledge, remembering probably the most important—certainly the most traumatic—event in their lives, disagreed on one major point, and it has remained a mystery for more than 80 years: Did the Titanicbreak apart at the surface or sink intact?
Although all the officers testified that the ship sank intact, some survivors and crew testified to a hull failure at the surface. Even during the American and British inquiries into the disaster, few questions focused on the structural aspects of the ship. Despite survivors' testimonies, it was concluded that the ship sank intact.


Evidence from the DepthsThe mystery arose again when the wreck of the Titanic was discovered in 1985 and the hull was found in two pieces. Many theories were developed as to how the ship broke apart during the sinking process, and research was begun to determine how this could have happened. The speculation intensified further when the wreck site was revisited in 1986 and a third 17.4-meter section from the midship region of the ship was found.
To help solve this mystery, the Discovery Channel, in developing its award-winning "Titanic: Anatomy of a Disaster"television documentary, approached Gibbs & Cox, Inc., one of the oldest naval architecture and marine engineering firms in the world. Gibbs & Cox agreed to perform a stress analysis to help determine the possibility of hull fracture at the surface.
With funding provided jointly by the Discovery Channel and the Society of Naval Architects and Marine Engineers, Gibbs & Cox conducted a basic study of the breakup of RMSTitanic using linear finite-element-analysis (FEA) software. This study was done in conjunction with materials testing of the Titanic steel by the University of Missouri-Rolla, with advice from Prof. H.P. Leighly Jr., Dr. Timothy Foecke, and Dr. Harold Reemsnyder of the Bethlehem Steel Corp.'s Homer Research Laboratory in Bethlehem, Pa.
Important to the analysis effort was accurate weight and buoyancy data for the ship at the time it struck the iceberg, and then later while it was sinking. These data were provided via a recent study of the ship's breakup undertaken for another technical paper, "The Titanic and Lusitania, A Final Forensic Analysis,"published in a 1996 issue of Marine Technology. The study provided the loading information needed to take "snapshots"of the ship's state of stress during the sinking process. Tests conducted on the steel recovered from the wreck site were performed at the University of Missouri and the National Institute of Standards and Technology in Gaithersburg, Md. The results from these metallurgical tests of Titanic steel and rivets were also input as data for the finite element analysis.
Gibbs & Cox engineers selected MSC/NASTRAN, from the MacNeal-Schwendler Corp. in Los Angeles, to perform the analysis. FEMAP engineering-analysis modeling and visualization software from Enterprise Software Products in Exton, Pa., was used to perform the pre- and postprocessing of the analyses. Gibbs & Cox had been using MSC/NASTRAN for approximately five years. According to David Wood, the firm's structures department manager, MSC worked closely with his team during the development of MSC/NASTRAN Version 70 to provide the special program solutions needed for use in their industry.
Engineers analyzed the stresses in the Titanic as the flooding progressed within the bow region, using modern FEA techniques that simply were not available until the 1960s, and certainly were not known to the structural designers of the ship in the first decades of the century. In the 1960s, engineers started to analyze the stresses in ship hulls using finite-element modeling (FEM). As a pioneer of FEA technology, MSC has been in the forefront of dramatically improving this technique to take advantage of advances in computer technology.
A full-ship model was graphically constructed, employing a modern approach similar to that used for U.S. Navy destroyers and cruisers today. Loadings for the model were developed based on one flooding scenario from the paper, "The Sinking of the Titanic,"by Chris Hackett and John C. Bedford.
The corresponding weight and buoyancy curves, developed by Arthur Sandiford and William H. Garzke, Jr., were used to model the critical flooding conditions believed to represent the hull loading just prior to hull fracture. Since the flooding process took place over several hours, a quasi-static analysis was considered appropriate. The initial modeling effort focused on the determination of the location and magnitude of high-stress regions that developed in the hull while she remained on the surface.
Engineers determined that stress levels in the midsection of the ship were at least up to the yield strength of the steel just prior to sinking. When considered alone, stresses at these levels do not indisputably imply catastrophic failure. Additional analyses, focusing on probable locations of initial hull fracture, are required to indicate that the ship sustained possible catastrophic failure at the surface and began to break apart.
Significant stresses were developed in the vicinity of the two expansion joints, and in the inner bottom of the ship between the forward end of Boiler Room No. 1 and the aft end of the Reciprocating Engine Room. Structural discontinuities, such as expansion joints, result in stress-concentration development. Typically, stress concentration levels are three to four times that of free-field stresses. While these structural discontinuities have not yet been thoroughly investigated, it is believed that stresses developed at these locations were significantly higher than the material yield stress.

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SHIP STABILITY – WHAT IS IT AND HOW DOES IT WORK?

By Patrick J. Bray, Naval Architect 

Stability is the ability of a vessel to return to a previous position.  Positive stability would
then be to return to upright and negative stability would be to overturn.  Stability in it’s most ba-
sic form is the relationship between the center of all floatation in your hull (center of buoyancy,
or CB) and the center of all weight (vertical center of gravity, or VCG).  In other words, the
downward pull of Gravity and the uplifting force of Buoyancy.  These are the primary charac-
ters in this scene and all others play minor roles.  Once you understand how their relationship
works, understanding stability becomes a simple matter



Static stability 

This is stability at rest without active external forces at work.  The VCG for all intended purposes is a fixed point in space and is a reflection of the placement of major weights within the boat affected in part by the amount of superstructure and number of decks. The shape of the hull determines the CB, which is not fixed.  It moves around to balance the loads and keep the forces in equilibrium.  The shape of the hull has a major effect on the path that the CB will take as the vessel heels or trims.  At rest the CB and the VCG align vertically.  If they are not vertically aligned then the vessel will change trim or list until they do come into alignment.  Then all the forces are equalized and the vessel becomes stable.  


Form stability (effects of section shape) 

As the boat heels, sides of the boat previously above water are immersed and bottom sections previously underwater are now exposed, and the CB is on the move.  The battle has begun.  As forces are applied to the vessel changing it’s attitude in relation to the surface of the water.  This causes the CB to move, creating the forces to bring the vessel into equilibrium.  If the CB can not create enough counterforce to right the vessel then it will be over turned.

The amount of counterforce can be determined mathematically from the designer’s
drawings and verified on the finished boat with an inclining experiment.  How are these calcula-
tions performed, you ask?  Someone needs to do a weight calculation, which accounts for every item on the entire boat right down to the weight of the paint and screws, and also accounts for their position in the vessel both vertically and fore and aft.  Usually transverse measurements are considered less critical as most boats are very symmetrical.  Knowing where the VCG is (remember, this is a fixed position) we can now go on to look at where the CB moves for each angle of heel.  This is also calculated, but in a far more complex manner and is best done by and experienced Naval Architect (and their computer).  Both hull form, and ballast if
any, have a major role to play out in this scene.  Both will have a major effect on stability, but more on that later.


Dynamic stability 

Once a vessel is under way the effects of wave train, bottom pressure and change of trim can add or detract from the amount of stability.  Many planing hulls become more stabile at speed due to the change in pressure distribution across the hull bottom.  Because of the V-bottom and the spray rails outboard, unequal pressure builds up on the lower side in a turn.  This pressure restores the vessel to upright when the heeling forces of the turn are over. Some double-ended vessels become less stable at hull speed because of the wave hollow amidship.  With only the fine forward and after sections floating the boat and the Midship section mostly unsupported there is little width to provide stability.  This can also be a problem to any vessel in short steep seas. Active and passive stabilizer systems give the impression of increasing stability; however they actually act to reduce roll.   In fact, active stabilizers are only effective when underway.  
 
The Coast Guard sets minimum standards of stability for various types of commercial craft but no such
standard is set for yachts.  Fishing vessel standards can be used as a guide as they have similar characteris-
tics and are a similar size to many offshore cruising powerboats.  However, these are minimums and do not address comfort.  And even comfort is subject to personal interpretation.  A serious offshore vessel will be tender initially and will tend to have a long easy rolling motion which will not knock crew nor gear off the deck.  For many pleasure boaters this amount of roll and length of time (period of roll) is alarmingly long.
If a boat is very stable at the dock (great as a liveaboard), or in flat water, it can have a very quick motion at sea.  A case in point is a very successful 110 ft motoryacht that does harbor charters seating 95 for dinner cruises.  When taken to sea it has such a quick motion in a seaway that the crew have to go around on their hands and knees to keep from getting knocked off their feet; and this is at 8 knots. Stepping aboard a 60 footer that noticeably settles under your weight (low GM) does not instill confidence.  Having it heel under the press of a strong breeze will only erode that confidence further; yet it can have an excellent sea motion and be extremely comfortable once you get your sea legs.  
            For the general boating public there has to be a middle ground.  Few boaters spend all their time at sea and just as few plan to spend all their aboard time at the dock (although sometimes it works out that way!).  A compromise must be struck: one that provides stability for dockside comfort moving around the vessel and a suitable motion for safe operation in some kind of seaway.  The proportion of compromise depends on the purpose of the vessel and the market segment that it is appealing to.  What is the intended use of the vessel and what level of experience will the purchaser have?    
            Let’s look at the effects various elements of design have on the stability characteristics
of a vessel.  


Ballast 

Generally when people think of stability and ways to increase it they think of adding bal-
last.  Generally this will help - but not in all cases.  If ballast reduces the freeboard to the de-
gree that the deck edge enters the water at a much lower angle of heel, then the overall stabil-
ity is drastically reduced.  Again, it is the relationship between the hull form and the overall cen-
ter of weight that tells the story.  Removing top weight from as high up as possible will have a
greater effect than adding ballast low down.
Also, ballast will not do much to increase initial stability (stability at very low angles of
heel).  It’s real forté is at higher angles of heel.  Once the heel angle starts to reach or exceed
45 degrees ballast comes into it’s own.  Although this may provide real peace of mind, it does
little to improve a day to day  comfort situation.

Beam 

Wide beam will produce high initial stability (and low ultimate stability).  It is great for liveaboard space and comfort at the dock but taken to extremes it will produce an uncomfortable motion in a seaway.  The combination of extremely wide beam and low freeboard in a monohull can be dangerous, as the high initial stability reaches it’s peak at a very low angle of heel.  Once overturned the vessel becomes very stable inverted and has no desire to return to upright.







A catamaran is a classic example of widebeam and no ballast taken to extremes.  The interior volume and low heel angles make thesevessels very comfortable to liveaboard.  On theother hand, if one hull ever leaves the water thechances of seeing it re-enter the water upright isslim to none.  To compensate for this, specific
hull forms have been developed which allow highimmersion of one hull before the other hull leaves Inertia

One of the ways to improve the motion of an existing vessel is to alter the amount of inertia.  If you have a boat with a quick motion and want to slow it down try moving major weights horizontally outboard from the centerline.  This will increase the inertia and dampen out the motion.  By moving the weight horizontally rather than vertically you do not affect the overall stability.  If your vessel has a slow roll that you would like quickened, try moving heavy weights inboard or down as this will reduce the inertia and/or increase the stability.  For a quick demo on inertia try spinning around on a swivel chair and bring your arms or legs in and out.

Superstructure 

           Generally stability increases in strength until 45-60 degrees of heel (occasionally as high as 90 degrees) and then slowly diminishes to nothing at 90-120 degrees, (the critical angle or ultimate angle).  Rarely, the ultimate angle goes all the way to 180 degrees, making the boat self-righting.  Once the deck edge immerses the shape and size of the superstructure becomes a major player in shaping the course the CB will take.  For this reason it is important that the house be well constructed and that there are few openings for water to enter.  If there are wide side decks then the house will enter the water later reducing it’s effect on the stability curve.  If the vessel is flush decked with little in the way of a house then all stability must be gained from the hull form.  

Windage 

The very area of a large superstructure can act as a sail, heeling the boat to some degree.  If the stability is reasonable then this should not be a problem.  In fact, in some boats this press of wind actually acts to dampen rolling motions further producing an even more comfortable ride.  Unfortunately, it is not a sail area that can be reduced as the wind pipes up.

Waves 

All vessels will suffer from loss of stability on a wave face.  If the waves are short and steep, as in a shelving area, the situation becomes worse.  With the majority of the vessel supported by the buoyant ends there is little waterline width.  As the vessel heels the midsection falls into the trough.  This can induce deep rolling motions and even cause capsizing. Even a beam sea can create serious problems if the wave train coincides with the vessel’s natural rolling motion.  Luckily a small change in direction or speed is all that is required to
avert a progressively worsening situation.

Active stabilizers 

These stabilizers are usually gyro controlled and hydraulically activated fins which are placed amidship. Their dynamic forces return the vessel to upright when a heeling force is detected.  They can even compensate for a list.  Generally, they dampen rolling motions more than 80%, however they do not increase the vessel’s actual stability.  Unfortunately, they are not considered workable at speeds below 8 knots through the water.  Their forces and effectiveness diminish as speeds drop until at anchor or at the dock they provide no real effective-
ness.


Passive stabilizers 

These passive systems vary from Paravanes to Fixed Bilge Keels to antirolling ballast tanks.  Their primary feature is that they have few to no moving parts and are mechanically simple and therefore very reliable.  They are not as effective in dampening roll underway as an active system but do tend to be better roll dampeners at low speed and at anchor.  They will do nothing to increase stability but will dampen the forces acting on your
vessel.

Downflooding points 

All of the stability in the world will be of no use if there are openings in your hull or superstructure that will let water in to flood your boat.  Items such as engine room intakes placed low in the hull sides and leading directly into the engine room are a classic problem.  Even if the boat has a good range of stability, what good will it do when water is pouring in a large open vent?  It is like having a gaping hole in your boat waiting to gulp up water. Openings for interior ventilation also need to be placed carefully.  Non-watertight hatches to
hull compartments need to be checked so water cannot enter at low angles of heel. The effects of uncontained water inside a boat are unbelievable!  Water always runs to the low side, making matters worse and it is surprising

how much water weighs.  As the vessel rolls, the water shifts from side to side, producing a pendulum effect which increases the rolling even further.   Even uncontained water on deck has the effect of raising the VCG and reducing stability.  Large freeing ports (drainage openings) in the bulwark are necessary in order to get the water off the boat fast, before the next wave adds further to the burden on deck. Of course, once a hull has been damaged and water is pouring in, there is little that can be done if there are no watertight ubdivisions in you boat.  Commercial vessels not only are required to have watertight bulkheads but must be designed to remain afloat and stable with one and sometimes even two compartments completely flooded.

            Numbers for number crunchers 

            Hard and fast numbers are usually misleading, because there are so many variables that effect stability.  In addition few of the thousands of small craft are designed by a Naval Architect so in many cases these stability numbers are just not known. Having said that, for a mono-hull yacht that is expected to do extended coastal cruising, open ocean cruising, or any vessel that is expected to be caught out in really bad weather you
should look for the following;
• a minimum range of stability to 90° of heel and over 120° preferred
• a maximum righting moment (GZ) that occurs after 30° and preferably after 50°
• and a GM of at least 2 feet and preferably between 3 feet and 5 feet

GM is the most valuable number to consider, as it tells you the initial stability; the stability that you will notice day to day.  GM is actually the measurement between the VCG and the Metacenter (M—the point at which a vertical line taken from the heeled CB crosses the vessel’s centreline) as shown in this diagram. Low GM means the boat may be a bit tender to walk around on and heel a few degrees under wind pressure.  How-
ever, there may be a good overall range of stability, which you can check by looking at the Critical Angle or Ultimate Stability.  
  If it has a higher GM then more than likely there will be sufficient initial stability, andpossibly too much, however Ultimate Stability may be low.  The boat will have a quick jerky motion in a seaway but be very stable at the dock.


Good stability doesn’t ‘just happen’

Good stability can be, and should be, achieved during the design stage.  Careful placement of heavy items down low, and knowledgeable design of a hull form and superstructure that takes stability characteristics into account will produce a sound vessel with a good solid feel to it.  Attention to the numbers that determine the vessel’s final characteristics will produce a successful yacht long before the boat is launched.





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