Marine Engineering Study Materials

The ‘SAFELAUNCH’ life boat release gear mechanism for davit launched survival craft explained in this article allows simultaneous release of the hooks even with the life boat being drifting due to wind or tide whilst still attached to the davit falls. The hook assembly is opened by cables activated by operating the release handle assembly.

System Description

The release mechanism consist of two lifeboat release hook on forward and aft(1), hydrostatic interlock unit or diaphram (2), coxswain’s release handle assembly (3), hydrostatic interlock cable (4), aft hook release cable (5), forward hook release cable (6), fixing plate (7) and green locking pin (8) as shown in the figure below.

Before moving to the release procedure, function of all the parts shown above need to be explained.

Life Boat Release Hook

The hook is released when ‘release lever arm’ is turned in anti clockwise direction while ‘operating cable’ is pulled down. Please note that ‘locking or maintenance pin’ must be removed before operating the release hook. Locking pin must be always in position when the life boat is secured to the ship. ‘Locking or maintenance pin’ is nothing but a fall preventive device (FPD). It is colored green. Have a look at the actual images of the life boat hook below. Click on the thumbnails to enlarge.

       

Hydrostatic Interlock Unit or Diaphragm Unit 

Function of the ‘hydrostatic release unit’ is to ensure that the life boat hooks are released only when life boat is waterborne. When water pressure acts on the bottom side of the diaphragm, ‘hydrostatic interlock cable’ is pushed upwards and allow the movement of ‘coxswain’s release handle’. When this interlock is in place, ‘coxswain’s release handle’ cannot be moved.

Coxswain’s Release Handle Assembly

Coxswain’s release handle assembly is the one pulls the forward and aft hook release cables for releasing the same. To prevent accidental movement of the lever there are two safeties in place. Firstly, there is a ‘safety pin’ as shown which prevent movement of the ‘release handle’. This ‘safety pin’ must be removed before activating ‘coxswain’s release handle assembly’. Secondly, the ‘release handle’ to be moved up to release it from the side plate slots on the assembly, before it is turned to the aft direction.

As we discussed before with the ‘hydrostatic interlock unit’, ‘hydrostatic interlock cable’ must be pushed upwards by the diaphragm for the ‘release handle’ to be moved. Situation may arise like diaphragm fail operate and move the cable. In that case ‘release handle’ cannot be turned. To prevent this an ’emergency override handle’ is given as shown above, which can be manually moved up before releasing.

While lowering life boat, when boat touches water we can see the ’emergency interlock or override handle’ moves to the ‘open position’ as shown above. An inspection window is provided to check the position of the ’emergency interlock handle’. ‘Open position’ (which is painted as red) indicates that interlock is removed. Now ‘safety pin’ can be removed, ‘release handle’ can be lifted up and can be turned in aft direction for releasing hooks.

Have a look at the actual images of the coxswain’s release handle assembly below. Click on the thumbnails to enlarge.

                    

Now all the parts of the life boat release gear mechanism are explained. Let us move to the operating instructions.

Operating Instructions

Normal Release Procedure

1. On contact with the water, ensuring the life boat is totally waterborne, remove the ‘safety pin’ from the ‘coxswain’s release handle assembly’.
2. Confirm via inspection window that, the hydrostatic interlock unit has operated successfully in moving the ’emergency interlock handle’ to the open position. (i.e. the red area)
3. Lift the coxswain’s release handle up (against the reaction of the return spring) until the spigot pins are clear of the side plate slots, then pull the handle back to its full extent.
4. Proceed to sail away.

Emergency Release / On load Release Procedure

In situation where the life boat is waterborne and the safety pin from the ‘coxswain’s release handle assembly’ has been removed, but the hydrostatic interlock unit has failed to move the ’emergency interlock handle’ into the open position or red area, the following procedure must be adopted. (The procedure is same for ‘on load release’ where the life boat is not waterborne.)

1. Break the inspection window glass to gain access to the ’emergency interlock handle’ and push it upwards and hold it in the open position (i.e. the RED area).
2. Lift the coxswain’s release handle up (against the reaction of the return spring) until the spigot pins are clear of the side plate slots, then pull the handle back to its full extent.
3. Proceed to sail away.

Life Boat Launch and Recovery Procedure

This section describes the procedure for launching and recovery of the life boat for drills.

Launching

1. Before entering life boat, ensure that the forward and aft hook ‘release lever arms’ pointing to the GREEN safe position.
2. Enter the life boat and ensure that, (a) the coxswain’s release handle is in the closed position, (b) the safety pin is fitted in the release handle assembly and (c) the ’emergency interlock lever’ is in the GREEN safe position.
3. Fit the GREEN handled locking pins to the forward and aft hooks.
4. Disembark the life boat and then; (a) remove the gripe wires if fitted, (b) carry out pre-launch checks.
5. Allow crew to enter the life boat and ensure all crew are strapped in.
6. Lower the life boat until the keel is just above the water.
7. Instruct two crew (one forward and one aft) to remove the GREEN handled locking pins from the hooks.
8. Instruct both the crew members to return to their seats and strap in.
9. Lower the life boat fully to the water and carry out ‘normal release procedure‘ as explained above.

Hook Reset and Recovery

1. For hook reset, rotate both hooks back into closed position ensuring the hook tail is behind the cam.
2. Return the coxswain’s release handle to the closed position and the hooks are now automatically reset.
3. Confirm the ‘release lever arms’ of forward and aft hook pointing to the GREEN safe position.
4. Attach each davit fall by inserting chain link into the hook.
5. Ensure that chain link is suitably seated.
6. Ensure that all crew are strapped in.
7. Hoist the life boat until the keel is clear of the water.
8. As soon as the life boat leaves the water during hoisting, ensure ‘hydrostatic interlock unit’ returns to the closed / GREEN safe position.
9. Instruct two crew (one forward and one aft) to insert the GREEN handled locking pins into the hooks, and then return to their seats and strap in.
10. Insert the ‘safety pin’ to the coxswain’s release handle assembly.
11. The life boat can now be recovered.
12. Ask the crew to disembark.
13. Stow life boat.
14. Remove the GREEN hook locking pins.

Reference and Images:

Survival Craft Inspectorate, SAFELAUNCH Release Gear