2.3 Inflatable Liferafts, Lifeboats & Launching Appliances

Inflatable Liferafts, Lifeboats & Launching Appliances

Quick Reference: Inflatable liferafts are primary survival craft engineered under SOLAS Chapter III and the LSA Code. They incorporate dual independent buoyancy chambers, an automatic insulated canopy, and hydrostatic release systems. The Hydrostatic Release Unit (HRU) triggers at 1.5 to 4.0 meters depth, cutting cradle lashings; the raft inflates at the surface, and the weak link (2.2 kN ± 0.4 kN) breaks to prevent the sinking ship from dragging the raft down.

1. Inflatable Liferaft Engineering & SOLAS Standards

Inflatable liferafts are designed to withstand 30 days of exposure in all sea conditions and operate across temperatures from -30°C to +65°C (-22°F to +149°F).

+-------------------------------------------------------------------------+
|                    SOLAS INFLATABLE LIFERAFT ANATOMY                    |
|                                                                         |
|         [ Exterior Light (0.75 cd, 8 hrs) & Rainwater Collector ]       |
|                                    /                                    |
|                      +--------------------------+                       |
|                      |  Double-Walled Canopy    |                       |
|                      |  (Air Insulation Gap)    |                       |
|                      +--------------------------+                       |
|                         /                      \                        |
|        +--------------------+              +--------------------+       |
|        | Upper Buoyancy Tube|              | Upper Buoyancy Tube|       |
|        +--------------------+              +--------------------+       |
|        | Lower Buoyancy Tube|              | Lower Buoyancy Tube|       |
|        +--------------------+              +--------------------+       |
|                      |                              |                   |
|                      +------------------------------+                   |
|                      | Inflatable Insulated Floor   |                   |
|                      +------------------------------+                   |
|                         /            |             \                    |
|          [ Water Ballast Pockets ] [ CO2 Bottle ] [ Boarding Ramp ]     |
+-------------------------------------------------------------------------+

Core Structural Components

1. Dual Independent Buoyancy Tubes: Constructed from high-tensile elastomer-coated nylon. Divided into separate upper and lower buoyancy chambers, each equipped with non-return inflation valves and pressure relief valves. If either chamber is punctured or deflated, the remaining tube maintains sufficient positive buoyancy to support the entire certified capacity of occupants sitting upright.
2. Double-Walled Insulated Canopy: Self-erecting arch canopy supported by inflatable canopy arches. The double fabric layers trap an insulating air barrier that prevents solar heat gain in the tropics and retains metabolic heat in polar waters. Features an observation port, entrance closures, retro-reflective tape, and an external rainwater catchment gutter feeding into a clean plastic hose inside.
3. Insulated Inflatable Floor: Features a double-layered inflatable floor that traps an air cushion, isolating occupants from the conductive cooling of freezing ocean water.
4. Water Ballast Pockets (Under-Floor Stabilizers): 4 to 8 heavy-duty fabric pockets mounted symmetrically beneath the floor. They automatically fill with 200 to 400+ liters of seawater upon inflation, lowering the center of gravity, resisting wind overturning moments up to 30 knots, and preventing capsize when survivors board one side.
5. Boarding Ramp & Interior Lifelines: An inflatable boarding ramp and semi-rigid ladder extend into the water to facilitate boarding from the sea. Internal lifelines give occupants handholds during rough seas.

2. Hydrostatic Release Units (HRU) & The Weak Link Mechanism

When a vessel sinks rapidly, liferafts must automatically release and inflate without human intervention.

+-------------------------------------------------------------------------+
|                   HRU & WEAK LINK FLOAT-FREE SEQUENCE                   |
|                                                                         |
|  1. Ship sinks -> Water pressure at 1.5 - 4.0 m activates HRU diaphragm |
|  2. HRU knife cuts canister cradle lashings -> Canister floats free     |
|  3. Ship sinks deeper -> Painter line unspools to full length           |
|  4. Painter reaches end -> Pulls gas release pin -> Raft inflates       |
|  5. Raft buoyant uplift exceeds 2.2 kN -> Weak link breaks cleanly      |
|  6. Fully inflated liferaft floats freely on surface                    |
+-------------------------------------------------------------------------+

The Engineering Mechanics

• Operating Depth: The HRU contains a spring-loaded knife blade held back by a hydrostatic diaphragm. Water pressure at a depth of 1.5 meters to 4.0 meters (5 to 13 feet) compresses the diaphragm, releasing the blade to sever the securing lashings (senhouse slip harness).
• The Painter Line: A high-strength line (10 to 28 meters long) connected between the raft's gas release valve and the ship's structure.
• The Weak Link: A specially calibrated link with a breaking strength of 2.2 kN ± 0.4 kN (approx. 500 lbs / 225 kg) positioned between the painter line and the ship's deck strong point.

• Servicing Intervals: Standard metal HRUs require annual shore-based inspection and recertification. Disposable composite HRUs (e.g., Hammar H20) have an operational service life of 2 years from date of installation with no servicing required.

3. Manual Launching & Boarding Methodologies

Throw-Overboard Liferafts (Step-by-Step Manual Launch)

1. Inspect Overboard Zone: Verify the launch area below is clear of personnel, debris, projections, and operating propellers.
2. Check Painter Attachment: Confirm the painter line is securely shackled to a reinforced deck strong point or the HRU weak link.
3. Release Lashings: Release the manual slip hook (pelican hook / senhouse slip) securing the canister to the cradle.
4. Cast Canister Overboard: Two crew members lift and heave the canister over the railing on the leeward side if possible.
5. Pull Painter & Inflate: Pull the painter line slack out by hand (typically 15 to 30 meters). When the painter is fully extended, apply a hard, sharp jerk. This pulls the internal firing cable, piercing the seal on the CO2/Nitrogen gas cylinder. Full inflation occurs in 20 to 30 seconds.

Davit-Launched Liferafts & Enclosed Lifeboats

• Davit-Launched Liferafts: Connected to a crane suspension hook, inflated at deck level, and boarded dry to full certified complement. Once loaded, the raft is swung out and lowered to the water. An automatic off-load release hook detaches tension the instant the craft becomes waterborne.
• Totally Enclosed Motor Propelled Survival Craft (TEMPSC): Rigid fiberglass hull with self-righting capability (rights itself from 180° inverted capsize if all occupants are seatbelted). Equipped with an internal compressed air system (provides 10 minutes of breathable air for engine and crew in toxic gas) and an external water spray deluge system (protects against burning oil pool fires for over 8 minutes).
• Free-Fall Lifeboats: Positioned on a stern ramp inclined at 30° to 45°. Occupants strap into backward-facing contoured seats with five-point harnesses. A mechanical release drops the craft, plunging it into the sea away from the ship.

Boarding Procedures: Dry vs. Water Entry

• Dry Boarding (Preferred): Boarding directly from the embarkation deck, marine evacuation slide, or pilot ladder without entering the water prevents cold shock and hypothermia.
• Water Entry Boarding: Approach the raft from downwind. Grasp the boarding ladder or ramp. Kick the legs horizontally to the surface while pulling the upper body onto the boarding ramp in a prone (face-down) position, rolling over the lower buoyancy tube into the craft. Assist subsequent survivors by pulling them under the armpits.

4. Righting an Inverted Liferaft

In heavy seas or severe crosswinds, a liferaft may inflate upside down. One survivor must enter the water to right it.

+-------------------------------------------------------------------------+
|                    INVERTED LIFERAFT RIGHTING SEQUENCE                  |
|                                                                         |
|  1. Approach inverted raft from downwind (leeward) side                 |
|  2. Locate CO2 gas cylinder on underside of lower buoyancy tube         |
|  3. Climb onto raft bottom; stand firmly on CO2 gas cylinder            |
|  4. Grasp heavy-duty righting straps across bottom of floor             |
|  5. Lean back using full body weight with back to the wind              |
|  6. Wind catches raft floor -> Raft rotates upright over survivor       |
|  7. CRITICAL: Immediately push clear and swim out from under canopy     |
+-------------------------------------------------------------------------+

1. Wind Alignment: Swim to the downwind (leeward) side of the inverted raft so that the prevailing wind blows against your back.
2. Locate the Inflation Cylinder: Find the steel CO2/N2 gas cylinder mounted on the lower tube.
3. Positioning & Grip: Climb onto the bottom of the raft, placing both feet securely on the gas cylinder and lower buoyancy chamber. Grasp the heavy webbing righting straps sewn across the bottom.
4. Leverage & Rotation: Lean backward with the full weight of your body, keeping arms straight. As you pull, your body weight levers the far side of the raft upward, allowing the wind to catch the underside floor and flip the raft upright.
5. Canopy Egress (Life-Saving Action): As the raft flips over, you will fall into the water beneath the canopy. Do not panic. Immediately orient yourself, locate the perimeter tubes, push clear of the canopy fabric, and swim out from underneath to prevent asphyxiation and entanglement.

5. The Sea Anchor (Drogue): Purpose & Deployment

The sea anchor (drogue) is a heavy-duty fabric cone attached by a bridle to the bow of the liferaft. It is one of the most critical survival appliances aboard.

• Deployment: The primary drogue is deployed automatically or immediately upon boarding. A trip line allows survivors to haul the drogue in for inspection or untangling. A spare drogue with hawser is stowed in the SOLAS equipment pack.