MAIB warning on Hammer HRUs

[tazzle]

One of the findings in the latest MAIB report on the sinking of the Auriga relates to the liferaft release. The vessel was fitted with an Ocean Safety 4 person ORC liferaft with a SOLAS approved Hammer HRU (yellow one). Recommendation is that 4-person liferafts are probably too small to trigger these and should be fitted with special weaker green ones.

I nearly bought one of the SOLAS HRUs at LIBS - on the basis that if it's SOLAS it must be OK - but glad I didn't now. You learn something new every day...

MAIB .pdf at http://www.maib.gov.uk/cms_resources/Auriga.pdf

 

[landaftaf]

strange report as they are triggered by water pressure and dont rely on the wieght of the liferaft /forums/images/graemlins/confused.gif

http://www.westpacmarine.com/safety_equipment/hydrostatic_releases.asp

 

[tazzle]

Yes, that's what I thought - but don't know enough about them. But MAIB clearly state (p10):

[ QUOTE ]
The Ocean Standard liferaft is a light duty raft designed for the leisure industry. The ORC pack contained in this raft is a basic survival kit with less stringent equipment requirements than either SOLAS “A” or “B” packs which are fitted to fishing vessels required to carry liferafts. Auriga’s liferaft was stowed on top of the wheelhouse roof, and was fitted with a standard Hammer HRU which is approved for SOLAS liferafts designed to carry six persons or more. As the liferaft was launched manually, there was no indication that the HRU was inappropriate for a raft of this size. However, there have been fears that smaller rafts of this type may not have sufficient buoyancy to break the weak link of the standard Hammar HRU, and it is recommended that they should now be fitted with the green Hammar HRU, which has an appropriate weak link. See Annex 2.

[/ QUOTE ]

 

[landaftaf]

it seems they are looking at the 'what if' scenario.
if the release isnt triggered by water pressure the weak link is supposed to release it anyway ..... so insufficient buoyancy means no liferaft breaking away from a sinking boat.

 

[salamicollie]

Isn't the weak link supposed to be where you attach the painter - it is meant to break if the Hammar releases (cuts lashing) and the ship goes down fast stopping the life raft (inflated or otherwise) being dragged down....

 

[landaftaf]

the weak link should be incorperated into th lashing to a strong point.
if the boat/ship sinks and the hydrostatic fails to operate the weak link should part releasing the liferaft. /forums/images/graemlins/cool.gif

 

[salamicollie]

Ah yes - its it a bit of both see

http://www.uscg.mil/d1/units/msoport/Saf...nstallation.pdf

 

[tugboat]

You are quite correct that the weak link is what the painter is attached to. The HRU is activated by water pressure allowing the raft to float off. As the vessel sinks the painter is pulled out of the canister until inflation is activated. The buoyancy of the raft then overcomes the weak link and and separates the raft from the sinking vessel. The weak link is not part of the lashing of the raft canister. It is there to cause auto inflation of the raft and then detach. The canister is usually secured in it's cradle by a V-shaped webbing strap, a senhouse slip, and the HRU and there is usually an adjustable lashing to allow adjustment of the strap (for different sizes of canister). I'm wondering if the MAIB report is suggesting that different HRUs have different sizes of weak link though I can see no reason for that.

 

[Sheff]

I'm definitely no expert on this type of automatic release, so only guessing.

I think the report is trying to say that, as the liferaft was manually launched, the hammar release doesn't come into play and then relies if the vessel it's attached to suddenly sinks on the buoyancy of a large commercial liferaft breaking the tether.

Presumably if it's a lightweight yachtie liferaft there's a danger it will be pulled under.

 

[salamicollie]

It looks like Hammar now have the weak link incorporated into the main tie down loop as piece of coloured plastic - hence the reference to colour...

http://www.cmhammar.com/

 

[tugboat]

Yes, but it's just a different way of doing the same thing. With either type, the weak link only comes into operation after the HRU has released and the painter extended. The weak link isn't part of the integrity of the securing arrangement of the raft, i.e. the HRU has to activate before the raft can be released automatically. If the raft is deployed manually the end of the painter stays attached to the ship with both types of weak link and has to be cut loose manually.

 

[landaftaf]

I remember being told the painter was a weak link .... i.e. the breaking strain of the painter was less than the buoyancy of the raft - at least with solas rafts
thus if the vessel sank, the hru opened and the raft floated free, the painter paid out until it activated the inflation bottle, then broke loose to float free.
that is what probably happened in the gypo ferry case as its reported there were rafts in the water. (though how there were lifeboats as well is a mystery if it sank so quickly) /forums/images/graemlins/cool.gif

 

[TheBoatman]

That's a perfect explanation as far as I'm concerned and exactly how I read it. It seems that MIAB are simply saying that a "lesser" strength HRU/weak link maybe more appropiate for small "pleasure" users L/rafts.
Peter.