7.2 Survival Craft: Lifeboats, Liferafts & Launching Appliances

7.2 Survival Craft: Lifeboats, Liferafts & Launching Appliances

When a merchant ship suffers catastrophic structural failure, uncontrollable progressive flooding, or uncontained cargo fires, crew survival depends entirely on the swift, orderly launching of survival craft. SOLAS Chapter III mandates that all cargo ships carry survival craft capable of accommodating 100% of the ship's complement on each side of the vessel, plus supplementary liferafts. Trainee General Purpose (GP) Ratings must master the construction, launching appliances, hydrostatic release mechanisms, operational equipment, distress pyrotechnics, and electronic signaling transponders that comprise modern maritime survival systems.

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1. Totally Enclosed Motor Propelled Survival Craft (TEMPSC)

Modern merchant vessels are equipped with Totally Enclosed Motor Propelled Survival Craft (TEMPSC) constructed from fire-retardant glass-reinforced plastic (GRP). Enclosed lifeboats provide shelter from heavy sea spray, wind chill and cold exposure. Protection from toxic cargo vapors requires a self-contained air support system.

+-----------------------------------------------------------------------------------------+
|                    TEMPSC CRITICAL OPERATIONAL SYSTEMS & SPECIFICATIONS                 |
+-----------------------------------------------------------------------------------------+
|  [ Self-Righting ]        --> Inherent positive stability; rights itself from 180° roll |
|                               when all hatches are battened and crew are seat-belted.   |
|  [ Propulsion Engine ]    --> Compression-ignition diesel; cold start at -15°C within   |
|                               2 min; runs with boat flooded to crankshaft; 24h @ 6 kts.|
|  [ Fire Protection ]      --> Engine-driven external water spray blanketing entire hull;|
|   (Fire-Protected Boats)      protects craft through fuel pool fire for >= 8 minutes.   |
|  [ Compressed Air System ]--> High-pressure air cylinders providing positive pressure  |
|   (Air-Supported Boats)       and breathable air for crew and diesel engine for >= 10 m.|
|  [ Free-Fall Launch ]     --> Stern ramp sliding release via primary mechanical hook or |
|                               secondary hydraulic actuator; absorbs water impact.       |
+-----------------------------------------------------------------------------------------+

Self-Righting Stability and Seating

• Self-Righting Capability: An enclosed lifeboat is designed with a high buoyant canopy and low center of gravity. If rolled inverted ($180^\circ$) in heavy breaking seas, the craft will automatically right itself within seconds, provided all access hatches are securely dogged shut and all occupants remain secured in their assigned seats with the fitted safety belts or harnesses.
• Occupant Restraints: Each seating position in a totally enclosed lifeboat has a safety belt that retains its occupant when capsized. Free-fall lifeboats have safety harnesses that also secure occupants during the launch. Fasten the fitted restraint as instructed before launch.

Tanker Lifeboat Safety Systems (Fire Spray & Breathing Air)

Oil tankers, chemical tankers and gas carriers carrying cargoes with flashpoints not exceeding 60°C require fire-protected lifeboats. Chemical tankers and gas carriers carrying cargoes emitting toxic vapors or gases require lifeboats with self-contained air support. The systems below provide these protections:

1. External Water Spray Deluge System:
   • Powered by an engine-driven centrifugal pump taking suction from a sea chest located in the bottom of the hull.
   • Discharges sea water through a network of copper or stainless steel spray nozzles distributed across the entire exterior surface of the canopy.
   • Must provide complete water coverage, protecting the craft and its occupants from a continuous burning oil or pool fire on the sea surface for at least 8 minutes.
2. Self-Contained Compressed Air Support System:
   • Comprises a bank of high-pressure steel or composite air cylinders installed inside the cabin manifolded to pressure-reducing stations.
   • Provides breathable air to all occupants while maintaining a positive internal pressure (preventing ingress of toxic petroleum vapors, $H_2S$, or smoke).
   • Must simultaneously supply clean combustion air to the diesel propulsion engine, allowing the engine to run normally while the air remains safe to breathe for at least 10 minutes with entrances and openings closed.

Lifeboat Propulsion Engine

• Engine Type: Marine compression-ignition (diesel) engine running on fuel with a flash point above $43^\circ\text{C}$ (closed-cup test). Spark-ignition (gasoline/petrol) engines are strictly prohibited.
• Cold Weather Starting: Must be capable of starting reliably at an ambient temperature of $-15^\circ\text{C}$ within 2 minutes of commencing the starting procedure.
• Starting Redundancy: Provided with either a manual starting system or a power starting system with two independent rechargeable energy sources. Starting arrangements and any necessary aids must remain accessible and satisfy the cold-start requirement.
• Flooded-Boat Operation: The engine must be capable of operating when water inside the lifeboat reaches the centerline of the crankshaft.
• Speed and Endurance: Must propel the fully loaded lifeboat at a speed of at least 6 knots in calm water for a continuous operational duration of not less than 24 hours.

Free-Fall Lifeboats

Many modern bulk carriers, container ships, and tankers employ Free-Fall Lifeboats positioned on inclined ramps over the vessel's stern.

• Launch Mechanism: The boat is launched by gravity alone without davit falls. Crew board the craft, strap themselves into backward-facing, contoured bucket seats fitted with head restraints, and the coxswain releases the primary mechanical release hook (or secondary hydraulic backup release pump). The boat slides down the ramp, plunges steeply into the sea clear of the ship's stern, and pops to the surface underway.
• Deceleration Impact: Backward-facing seats distribute water entry deceleration forces evenly across the seafarer's back and shoulders, preventing spinal compression.

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2. Inflatable Liferafts & Hydrostatic Release Units (HRU)

Inflatable liferafts serve as auxiliary survival craft on cargo ships and primary survival craft on smaller vessels. They are stowed inside weatherproof, cylindrical glass-reinforced plastic (GRP) canisters mounted on cradles on open weather decks.

                               FLOAT-FREE LIFERAFT SEQUENCE

     1. SHIP SINKS              2. CANISTER FLOATS            3. PAINTER LINE TRIPS          4. WEAK LINK SNAPS

    ~~~~~~~~ Water ~~~~        ~~~~~~~~ Water ~~~~           ~~~~~~~~ Water ~~~~           ~~~~ Fully Inflated ~~~~
     [=== Canister ===]          [=== Canister ===]              /   Canister   \            /      Liferaft     \
    --- Deck Cradle ---                 ^                       /                \          +---------------------+  
             |                          |                      +------------------+                   |  
    [ HRU cuts lashing ]         Canister floats                 Liferaft inflates                    |  Weak link breaks
     at 1.5 - 4.0 m depth         pulling painter               at full painter pull                  |  at 2.2 +/- 0.4 kN
             |                          |                                |                            X
             v                          v                                v                            v  Ship sinks away

The Hydrostatic Release Unit (HRU)

A Hydrostatic Release Unit (such as the Hammar H20) is a pressure-sensitive release mechanism that automatically frees the liferaft if the vessel sinks before manual launch can occur.

• Operating Depth: Actuates automatically at a water depth between 1.5 and 4.0 meters. Water pressure acts upon an internal rubber diaphragm, driving a spring-loaded stainless steel knife blade across a strong securing cord, releasing the cradle lashing strap.
• Service Life: Disposable HRU models have a service life of 2 years from date of installation aboard; non-disposable types require annual servicing by an approved service station.

The Float-Free and Weak Link Mechanism

1. As the ship founders and sinks beneath the waves, water pressure trips the HRU at a depth of 1.5–4.0 meters, cutting the lashing band.
2. The buoyant liferaft canister floats up out of its cradle toward the sea surface.
3. The canister remains tied to the sinking vessel by its long painter line, which is connected to the cradle via a calibrated Weak Link.
4. As the ship continues sinking deeper, the entire length of the painter line (typically 15 to 30 meters) is pulled out from the canister.
5. When the painter line runs out completely, a sharp tug trips the internal high-pressure cylinder operating valve, discharging $CO_2$ and nitrogen ($N_2$) into the liferaft chambers. The LSA Code requires inflation within 1 minute at 18–20°C and within 3 minutes at −30°C.
6. As the sinking ship plunges further, its downward pull exerts tension on the weak link.
7. The weak link breaks cleanly at a statutory breaking force of $2.2 \pm 0.4\text{ kN}$ (approx. 220 kg force), allowing the fully inflated liferaft to float freely on the surface rather than being dragged down into the depths.

Boarding, Righting & Immediate Survival Actions

• Righting a Capsized Liferaft: If a liferaft inflates upside down due to high winds or sea chop, a seafarer wearing an immersion suit or lifejacket must swim to the raft, climb onto the upturned bottom, stand on the high-pressure $CO_2$ inflation cylinders, grasp the molded righting strap on the underside, and lean backward with full body weight. The wind will catch the underside and roll the raft upright.
• Immediate Actions Inside the Liferaft (CUT-STREAM-CLOSE-MAINTAIN):
  1. Cut: Locate the floating safety knife (stowed in a pocket beside the main entrance) and immediately cut the painter line free from the sinking ship.
  2. Stream: Deploy the sea anchor (drogue) to slow drift, keep the raft head to sea, and reduce the risk of capsizing in breaking waves.
  3. Close: Close the entrance canopy flaps to preserve interior warmth, keep out cold spray, and reduce hypothermia.
  4. Maintain: Use the bailer and cellulose sponges to remove bilge water; inflate the insulated double-bottom floor using the manual bellows pump; issue seasickness (motion sickness) tablets to every survivor within the first hour (vomiting severely exacerbates dehydration and hypothermia).

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3. Statutory Survival Craft Equipment and Rations

Every certified lifeboat and liferaft is stocked with an emergency equipment pack (SOLAS A Pack for international seagoing ships):

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4. Marine Distress Pyrotechnics

Pyrotechnic distress signals provide visual location markers during search and rescue operations. All marine pyrotechnics must be stored in watertight containers and replaced before their statutory expiration date (typically 3 to 4 years from manufacture).

+-----------------------------------------------------------------------------------------+
|                        SOLAS MARINE DISTRESS PYROTECHNIC STANDARDS                      |
+-----------------------------------------------------------------------------------------+
|  [ Rocket Parachute Flare ] --> Altitude >= 300 m; luminous intensity >= 30,000 candela;|
|                                 burns brilliant red >= 40 seconds; descent <= 5 m/s.    |
|  [ Red Hand Flare ]         --> Luminous intensity >= 15,000 candela; burns red for     |
|                                 >= 1 minute (60 sec); produces no falling burning slag. |
|  [ Buoyant Smoke Signal ]   --> Discharges dense orange smoke for >= 3 minutes (180 s); |
|                                 floats upright on water; daytime aviation visual marker.|
+-----------------------------------------------------------------------------------------+

Safe Handling and Firing Rules

• Wind Direction: Use signals clear of the canopy and other survivors. Hold a burning hand flare downwind and outboard, following its printed instructions, so flame, sparks and smoke travel away from people and the craft.
• Firing Angle: Fire a rocket parachute flare vertically upward as its printed instructions direct, holding it firmly clear of obstructions and turning your face away. Keep its firing end away from people; hand flares have separate handling instructions.
• Eye Protection: Never look directly into the firing tube or at the blinding magnesium flame.

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5. Electronic Distress Beacons: EPIRB & SART

Modern search and rescue operations rely primarily on electronic distress alerting and homing devices carried in survival craft.

Emergency Position Indicating Radio Beacon (EPIRB)

An EPIRB is an automated radio transmitter designed to alert search and rescue authorities via satellite immediately upon vessel abandonment.

• Operating Frequencies:
  • 406 MHz Satellite Signal: Transmits a digital burst carrying the unique coded beacon identity, country code and encoded GNSS position where provided to the international Cospas-Sarsat system. The identity may be based on an MMSI, serial number or radio callsign and must match the beacon registration.
  • 121.5 MHz VHF Homing Frequency: Low-power homing signal used by search aircraft and rescue vessels to steer directly to the beacon's physical position.
• Mounting and Activation: Installed on the open bridge wing or monkey island in a float-free cradle with its own dedicated Hydrostatic Release Unit. If the ship sinks, the EPIRB floats free, activates automatically upon immersion in seawater via conductive seawater contacts, and transmits continuously for at least 48 hours.
• Testing: Must be tested monthly by ship's officers using the integrated "Test" switch without sending a live false alert.

Search and Rescue Transponder (SART)

A SART is an electronic radar transponder designed to locate survival craft on marine navigation radar displays.

• Operating Frequency: Operates on the 9 GHz X-band ($3\text{ cm}$) marine radar band. (SARTs do not trigger 3 GHz S-band radars!).
• Radar Display Pattern:
  • When illuminated by an X-band radar pulse from a searching vessel or aircraft, the SART transmits a coded response.
  • On the searching radar screen, this response displays as a straight line of 12 distinct dots spaced 0.6 nautical miles apart, extending outwards along the line of bearing from the SART's location.
  • As the rescue ship closes to within approximately 1 nautical mile, the 12 dots blur into wide arcs, and eventually into concentric circles surrounding the radar sweep, warning the bridge team that the survival craft is immediately adjacent.
• Mounting and Elevation in Survival Craft:

  Important

  To achieve maximum radar detection range, the SART must be mounted at least 1 meter above sea level. Inside an inflatable liferaft, crew must mount the SART on the telescopic fiberglass pole provided, protruding through the top canopy sleeve, or hang it from the internal canopy arch pocket. At 1 meter height, a ship's radar ($15\text{ m}$ antenna height) can detect the SART at roughly 5 nautical miles, while a search aircraft ($3,000\text{ ft}$ altitude) can detect it at over 30 nautical miles.

• Battery Operational Life: Minimum 96 hours in passive standby listening mode, followed by at least 8 hours of continuous transponding interrogation.