More liferafts

[bedouin]

This may seems a silly question, but following on from the thread on liferaft storage....

Consider a yacht foundering with the liferaft on deck, with the painter tied on but otherwise unattached.

(a) As the boat sinks, will the buoyancy of the liferaft canister be sufficient to cause the liferaft to inflate.

(b) If the liferaft does inflate, will the buoyancy be sufficient to cause the painter to part, or will the liferaft be dragged under?

The answers may have a significant impact on my plans!

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[jimi]

there is a hydrostatic thingie (to use a technical term) which activates a blade to cut the line when a certain water pressure is reached.

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[snowleopard]

sorry, don\'t believe you

some owners use separate hydrostatic releases to free the raft if the boat sinks. rafts don't incorporate such a device (too expensive). i suggest you check with the manufacturer before you buy but i think they rely on a weak link which will fail before the painter rips a hole in the raft (no way will the raft go under).

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[jimi]

Re: sorry, don\'t believe you

Sorry if I did'nt make myself clear, I was referring to a seperate hydrostatic release fitted to the line not to the raft. I bought mine with the liferaft.

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[pvb]

Not a silly question at all...

Quite an interesting question. A canister liferaft will float, but I doubt that it has enough buoyancy to trigger the inflation mechanism in the scenario you've posed. Last time my liferaft was serviced, I went along and set it off. I was amazed at how hard you have to pull the cord! Maybe we should ask liferaft makers for answers.

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[jimi]

Re: Not a silly question at all...

have a look at

<A target="_blank" HREF=http://www.dssmarine.com/prod09.htm>http://www.dssmarine.com/prod09.htm</A>

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[Twister_Ken]

Re: sorry, don\'t believe you

Current 'Sailing Practical Yachtowner Today Monthly' says there is no weak link in the painter, but there is a mickey mouse knife secured near the raft door to cut the painter.

For those on the S Coast can I draw your attention again to

<A target="_blank" HREF=http://www.messengermarine.co.uk/openday.htm>http://www.messengermarine.co.uk/openday.htm</A>

I'm going to try and be there with my liferaft altho' SWMBO has booked us to go skiing the next day (oh joy).

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[tcm]

Re: sideslipping holiday

oho, where you going? The high alp places have lots of snow.

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[Piers]

For excellent and accurate advice, try calling John Baker at Nationwide Liferafts. He's helped many people on this forum. Real enthusiast. 019252 45788, or mobile 07885 631066.

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www.playdeau.com

 

[jonjo]

Re: Wrong issue

I think your concerns are misfocussed.

The biggest problem faced is getting the whole crew directly into the raft. To achieve this you don't want the raft to inflate until you are ready i.e. the crew is on deck together and know what to do.

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[Mirelle]

They work on ships, why not on yachts?

There are plenty of cases of merchant ships sinking very quickly, either because of an explosion or because of structural failure when carrying a dense bulk cargo like iron ore. In many cases there was no time to send a distress message, yet the liferafts usually pop up and are found inflated (and empty) when the EPIRB is homed on. Clearly, their hydrostatic releases operated as intended.

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[bedouin]

Answering my own question...

Couldn't find any useful information on manufacturers sites, but looking at the ORC/RORC requirements they say (among other things):

(a) That the force on the painter required to inflate the liferaft must be <150kN.

(b) That the breaking strain on the painter must be such that it can't be dragged under by a sinking yacht.

Now I calculate that the buoyancy of an average canister is 300-500kN, so there should be no problems.

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[AndrewB]

Intrigued ...

You are proposing to keep a liferaft on deck attached only by the end of its painter?

Can it be that there is some hitherto little known IRC rating allowance for yachts carrying liferafts likely to explode unexpectedly into action midrace? The rest of us need to know.

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[bedouin]

Re: Intrigued ...

No - that wasn't really the plan, just trying to set the parameters within which to operate.

Basically I am happy with the liferaft being stowed in the stern locker - the only time I can see that being a problem is in the case of collision - which would imply fog. I have been wondering about an alternative external mounting mechanism for fog or general light weather conditions, and wanted to make sure that if the liferaft was secured to the boat by the painter (only) then it would deploy successfully.

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[30boat]

I think I read on PBO that that is only a mith.

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[wayneA]

Hi Bedouin

I've just recently completed a sea survival course at Fleetwood Naval College, in the survival centre there. The course, also used by the Merchant Navy, covered the auto deployment of liferafts from sinking/sunk ships.

This was achieved by having a hydrostatic activated blade, that released the canister from the cradle by cutting a line that secured the cradle closed. Once free, the buoyancy of the canister pulled against the painter at the correct pressure to inflate the, now underwater, raft. The end of the painter is secured to the ship/cradle by a second, thinner line that is designed to break under the load of the inflated raft's buoyancy – allowing it to float free to the surface ‘after’ inflating.

The course was aimed more toward larger ships, but I’m sure any yacht could use the same approach.

Cheers

Wayne


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[Dave99]

Lots of people seem to want to connect their liferaft to the boat with the painter only. How are you going to do that? keep it loose on deck?

The whole point of a hydrostaic release is to release the lashings holding the container to the deck/pushpit. Then the natural buoyancy of the container is enough to set off the inflation, which in turn breaks the relatively thin painter.

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[wayneA]

Yes - As I mentioned - The hydrostatic blade cuts a line that secures the 'CRADLE' closed. The cradle holds the liferaft canister in place on the deck.

Also, it was recomended to secure the painter to the ship/cradle by a second, thinner line that was sure to part at the correct load to release the raft after inflation. We were deploying 16 man rafts at the time, with quite thick painters, so maybe a small raft's painter would part easier - thus not requiring the second line?

Wayne

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[Gunfleet]

That sounds very difficult to specify. Strong enough to tug the painter hard enough to inflate the raft, weak enough to break immediately afterwards. It would have to be very precise, don't you think?

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[qsiv]

Re: Answering my own question...

Let's just think ..

6 man raft 2m diameter
Floor area = 12 sq m
Hight of tubes .4 m

Volume (until downflooding of raft) 4.8 m3

Potential bouyancy ~ 5000 kg

Most lite stuff would fail before this.

I appreciate this is oversimplified (the raft will heel, and be dragged under at an angle), but any thin line would serve as a weak link.

Personally (and cos the raft is in a locker), I dont have such a link - it will need people to launch raft so the issue shouldnt apply. We do have a dinghy on davits, and a further avon rollaway as well, when we are not racing.
6 Person Raft = 13.6 cuFt

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