Lifesaving Systems

Lifesaving Systems

The lifesaving system on a ship is a vital part of the ship and is an extension of the emergency escape route. A designer should view the fitting of lifesaving equipment in concert with the fire protection design and the emergency escape routes.

General Design Considerations

1. Survival craft should be provided with sufficient capacity and so distributed that all persons on board can be accommodated under adverse ship and weather conditions.

2. Survival craft should be launchable within the shortest period of time even if the ship machinery is not running.

3. Stowage of survival craft should be in well lit areas with ample space for supervision.

4. Launching should not put the craft in danger of being damaged by the propeller or overhanging hull structure.

5. A reasonable percentage of the survival craft should be released automatically to an operative condition.

Specific Design Considerations

a) Longitudinal Location

In general, lifeboats should not be closer to the bow than ¼ the ship’s length and should not be located so far aft as to be endangered by the propellers.

b) Vertical Location

The vertical location of lifeboats and liferafts should be selected with care to avoid damage to them by boarding seas. The uppermost deck extending to the sides of oceangoing passenger ships is generally sufficient. On cargo ships this deck could be so close to the waterline.

c) Clearances

Minimum openings on the ship’s sides between decks should exist so that lifeboats will not hang up in such openings during launching under an adverse list. Also there should be enough clearance between the inboard side of the lifeboat and the house side.

Marine Outfittings Prof. Dr. Yousri Welaya

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Lifeboats

They are either enclosed or of open construction and are made from either galvanized steel, aluminum or GRP. According to the means of propulsion, they are either oar (≯ 60 persons), hand crank (≯ 100 persons) or motor propelled (> 100 persons).

Lifeboats range in size from 3.7 m 6-person boats used on tugs and other small vessels, to 11.3 m 150-person boats used on large seagoing passenger ships.

Substitution of inflatable life rafts for up to 25% of the required lifeboats is a way to relieve space limitation problems. Such rafts must be capable of being lowered to the water fully loaded by an approved launching device one of which must be installed on each side of the vessel. The entire launching operation, boats and rafts included, must not exceed 30 min. This normally dictates that no more than five rafts be served by each davit..

The releasing gear for lifeboats should be of a type which will release both ends simultaneously whether under load or not.

Today, ships are often fitted with lifeboats that are totally enclosed. This protects those inside from the weather, but also means that the crew have a better chance of escaping if their ship has a dangerous cargo which is leaking. Imagine trying to escape from a tanker whose cargo is leaking on to the sea and is ablaze. Where possible, the lifeboat is mounted on a steep ramp fitted above the stern of the ship. This means that it can be launched even if the ship has a heavy list and it can safely move away from a burning ship.


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Free Fall Lifeboats

Free fall lifeboats are located at the stern of a ship. Examples of free fall lifeboats used on merchant ships are shown below:


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The launching of a free fall lifeboat is entirely based on gravity without the use of any wire falls. After the release hook is opened, the boat starts to slide along the skid, has a short free fall and enters the water. Due to its forward motion, the boat sails immediately away from the ship and reaches a safe distance within seconds from the moment of release.

The lifeboat is boarded through an aft door with access to the seats on either side of the central aisle. The seats can be front facing as well as rear facing. Typical rear facing seating arrangement is shown in Figures. Passengers are strapped into their seats with safety belts. The average capacity of free fall lifeboats varies between 8 and 90 people.


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Procedures for use

Launching

The free fall lifeboat shown below is stowed in skid (1), at the stern of the ship. This position at the ship ensures that even under a large list and trim, the release angle is still sufficient for a safe launch. If the lifeboat is launched from the sideboard, the release angle can become too small. From model experiments it is known that with a too small launching angle, the lifeboat can bounce back from the water like a floater. The lifeboat slides on rollers (2), which are connected to the skid, the launching ramp for the lifeboat. In some designs, the lifeboat slides on Teflon plates, which are vulnerable for wear.


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After embarkation of the passengers, the lifeboat can be launched by opening the release hook(s). This is controlled from inside the lifeboat. By opening a valve, a hydraulic circuit is opened and by pumping, pressure can be build up. The pressure is used to operate the release mechanism. Two persons are required for this operation, one to open the valve, the other for building up the pressure.

Embarkation

Embarkation into the lifeboat is via an aft door. Passengers take their seat and strap themselves in. Depending on the type of lifeboat, it can be necessary to strap the head as well. Because persons are strapped in, it is not possible to let them wear a lifejacket, unless it is an inflatable lifejacket.

The lifeboat

Most lifeboats are constructed of glass reinforced polyester or aluminum. They have a special designed shape to minimize acceleration during the impact. The maximum drop height is up to 35 m. Typical weight of the boat with equipment varies between 3000 kg for a 23 persons boat up to 17000 kg for a 90 persons boat.

Davit system

The free fall davit with an A-frame is shown in Figure. The davit system can also be used to lower the lifeboat via the wires. Then the boat is hooked up to the falls and lowered in a controlled manner into the water. This makes it possible to use the lifeboat in water with ice or other objects as well as in shallow water, where escape via a free fall is not possible.


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Rescue Boats

Rescue boats are to be provided with separate launching arrangements capable of both launching and recovery. The rescue boat may be included in the survival craft capacity. At least one of the rescue boats on ro-ro passenger ships which are certified to carry more than 250 passengers shall be a fast rescue boat. The rescue boat shall be fitted with a rescue frame for recovery of persons from the sea. Rescue boat embarkation and launching arrangements shall not take more than five minutes. A rescue boat shall be capable of being recovered in not more than five minutes when loaded with its full complement of persons and equipment. A rescue boat with crane is shown below.

There are different types of rescue boats. The rigid type is 4-6 metres in length, with outboard engine, covering speeds of 6-20 knots. Rigid inflatable rescue boats, 3.8 – 5.2 m long, with outboard engine or water-jet, reaching speeds of up to 35 knots are also available.

Liferafts

As well as lifeboats, ships carry other sorts of buoyant apparatus. On ferries and other craft which are never too far from land, the seats on deck are designed to float, and have lifelines attached. The hope is that rescuers will soon come along if the vessel sinks.

Liferafts are also very popular. They can be stored on deck easily and quickly inflated when needed. Unlike a lifeboat, they cannot be steered, and rely on rescuers finding them. High-sided passenger ships have marine evacuation systems, where chutes lead down to huge liferafts.


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Liferafts serve several purposes:

• They provide backup survival craft capacity for personnel working or sleeping remote from lifeboats locations or where access to lifeboats is cut off.

• They serve as survival craft ready for boarding if a ship sinks suddenly without time for orderly abandonment.

• Liferafts are considered an acceptable substitute for a missing or damaged lifeboat.

There are three types of liferafts:

1. Throw overboard liferafts

Throw overboard liferafts are designed to be used as independent units or as part of evacuation systems. They can be stored almost anywhere on racks and ramps, saving valuable deck space and causing minimal disruption to sea views which is important for passenger ships. They are packed in sturdy containers with a special sealing method that makes them especially durable, resistant to water ingress and makes them faster and easier to service. Liferafts are equipped with emergency packs and liferaft equipment according to SOLAS and flag requirements. They are provided with two individual buoyancy compartments. One compartment alone has sufficient buoyancy to carry the specified number of passengers.


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1. Shackle 2. Lifting arrangement/suspension straps (fitted on davit-launched liferafts only) 3. Rainwater catchment and collecting unit. Rainwater collecting bags and operational instructions inside 4. Internal grab line 5. Suspension strap 6. Patch for lifting arrangement 7. Upper buoyancy tube 8. Lower buoyancy tube 9. External grab line 10. Stabilizing pockets 11. Floor in middle 12. Floor at bottom 13. Boarding ladde

14. C02 cylinder 15. Arch tube 16. External, automatically activated light 17. Internal, automatically activated light 18. Arch tube 19. Inner canopy 20. Outer canopy 21. Retro-reflective tape 22. Viewing port 23. Double floor 24. Bilge arrangement 25. Drain 26. Double zip closure 27. Emergency pack

The above figure shows a 35 persons throw overboard liferaft for use on commercial vessels, fishing vessels, passenger vessels and offshore installations. The throw overboard liferaft is released from its cradle and thrown overboard, or slides automatically when released. Once waterborne, the liferaft inflates on a hard pull of the painter line and is then ready for boarding.

2. Davit-launched liferafts

Davit-launched liferafts are ideal supplements to slide and chute systems, providing safe evacuation for those unable to descend chutes or slides due to injury, disability or size. They can be launched from almost any type of vessel, regardless of deck height or hull shape.

The davit-launched liferaft is to be connected to the davit and then inflated at deck level, thus enabling the passengers to board the raft from deck. The liferaft is then launched to the water.


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3. Direct boarding liferafts

The direct boarding concept is the ideal rapid mass evacuation solution for vessels with low evacuation deck heights. The rectangular shape of the high capacity liferafts means they can be moored alongside the vessel, thus reducing the problem of unwanted movement during evacuation. Evacuees access the high capacity liferafts directly from the embarkation station or deck.

Total evacuation capacity is increased simply by adding more liferafts to the vessel. They can be stored on racks in remote areas and individually remotely released from the embarkation station. The liferaft can be pulled to the evacuation point manually or by using a winch. High capacity rafts are available for 51, 101 or 150 persons. The evacuation height is approximately 1.5 m.

Davits

Davits are specifically designed for safe and efficient launch and retrieval of lifeboats. They are designed to move lifeboats from their stowed position to an embarkation position, and subsequently to lower them to the water. Launching of the lifeboat is performed either from inside the boat or from a remote control unit. Recovery of the lifeboat is performed by the electric driven winch.


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Davits are classified as “Gravity Davits” which must be capable of being swung out without the use of manual, electric, steam or other power supplied by the ship. They consist generally of arms rolling on track ways or arms with one or more pivoting links. They are used whenever the weight of the lifeboat and its equipment exceeds 227 kg. “Mechanical Davits” are swung out manually by cranks, operating screws, gears or other mechanical devices.

Lifeboats are supported under davits by wire falls led through a series of sheaves to the drums of a lifeboat winch. Winches are required whenever gravity davits are used, and whenever the height of the deck on which lifeboats are carried exceeds 6 m from the lightest seagoing draft. A lifting speed of 0.1 m/sec is the norm. Powered winches are designed for operation by electric, hydraulic or pneumatic drive. Unpowered winches may be driven by a portable power unit, if required. All winches shall be provided with a facility for manual recovery of the lifeboat.

As required by the SOLAS, the falls used in launching shall be turned end for end at intervals of not more than 30 months and must be renewed at intervals of not more than 5 years or earlier if necessary due to deterioration of the falls.


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The Free-fall Davit System is a deck-to-wall mounted davit placed at the stern of the ship, and consisting of a launch ramp, davit arm (A-frame), winch and hydraulic unit. The launch ramp has sliding pads for smooth acceleration of the boat. In situations where free-fall launch is impractical or unsafe, the system has a secondary means of launching the lifeboat. Recovery of the lifeboat with the hydraulic driven winch.

The “Raft Davit” is shown in the following figure:


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Alternative Evacuation Systems

Ships in which the distance, in the lightship condition, from the waterline to the embarkation deck is 1.5 m or more shall be provided with marine evacuation systems. The systems shall, as far as practicable, be evenly distributed on both sides of the ship. Marine evacuation systems may consist of rigid or inflatable evacuation slides or vertical escape chutes which together with the associated liferafts and a platform, where applicable, constitute a complete evacuation system.

The Chute System

The chute and platform are housed in a compact box unobtrusively stored on deck. During an emergency, the crew release the chute and platform with a pull of a lever. The chute and platform fall to the water, and the platform automatically inflates. At the same time, the liferafts are launched from their racking system, inflated and attached to the platform. Passengers enter the chute by way of the housing and safely descend to the platform. They are then dry-transferred to the platform. They are then dry-transferred to the liferafts with rescue boat standing by to assist. The telescopic nature of the evacuation chute ensures a safe descent path and compensates for ship and sea movements so that evacuation is not obstructed. The evacuation capacity is 367 people in 30 minutes.


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Evacuation Slide System

The evacuation slide is a high capacity evacuation system that can be suited to match any ship design and capacity. The landing platform saves valuable time in an emergency situation as evacuation can commence before the liferafts are completely inflated. Several evacuees can descend the double slide at the same time and access the system liferafts from the landing station. The platform can also be disengaged from the slide and function as a supplementary rescue unit. The 30° angle of the slide compensates for sea and ship movement, even in heavy weather. It can evacuate 657 people within 30 minutes. The installation height is between 6 and 15m. The single track system is a compact version of the full sized double track system. It can evacuate approximately 250 people in 30 minutes. The installation height is between 3.5 and 7m.


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Radio transmitter

The most effective piece of lifesaving equipment on a ship, however, does not float at all: the radio transmitter. It can be used to summon help unless the disaster happens very quickly, in which case there is little chance of the boats or rafts getting away.

Now, there is even an automatic way of sending distress messages, the Global Maritime Distress and Safety System. Ships carry a radio set in a container designed to float off if the ship sinks. It then automatically sends out an alarm signal that is picked up by navigation satellites that can monitor its position very accurately.


Lifesaving Systems

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