Hydrostatic release on liferaft in knockdown

[webcraft]

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If you have a liferaft with a hydrostatic release and you are knocked down or rolled presumably it will inflate?

- W

 

[NorthUp]

Not necessarily- the Hammar unit used on most fishing boats needs 4 metres depth to operate reliably:
http://www.cmhammar.com/products/h20-for-liferafts/h20-small-rafts-model/

 

[Talulah]

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If you have a liferaft with a hydrostatic release and you are knocked down or rolled presumably it will inflate?

- W

Bigger issue in a knockdown is often the safety gear getting washed overboard. (Personal experience.) Anything on deck becomes sacrificial.

 

[fisherman]

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If you have a liferaft with a hydrostatic release and you are knocked down or rolled presumably it will inflate?

- W

No it will only release, then inflate if at the end of the tether.

 

[Ruffles]

Not necessarily- the Hammar unit used on most fishing boats needs 4 metres depth to operate reliably:
http://www.cmhammar.com/products/h20-for-liferafts/h20-small-rafts-model/

Which means that if you hit a rock and sink in shallow water it probably won't work at all!
What surprises me is that the valise is supposed to float before it inflates. Seems far too heavy. Does my back in every time I heave it on deck.

 

[fisherman]

Which means that if you hit a rock and sink in shallow water it probably won't work at all!
What surprises me is that the valise is supposed to float before it inflates. Seems far too heavy. Does my back in every time I heave it on deck.

If, worst case, the boat sank inverted, the liferaft could be trapped in a cradle. Also, if it sank so far that the air spaces in the canister were sufficiently compressed it would not float at all.

 

[prv]

Not necessarily- the Hammar unit used on most fishing boats needs 4 metres depth to operate reliably

Doesn't mean it won't operate at less though - especially given the higher water pressures swirling around inside a wave.

Pete

 

[webcraft]

No it will only release, then inflate if at the end of the tether.

If it releases in a knockdown or a rollover then there must be a good chance of it going to the full length of the tether.

Several units available in chandlers give a release depth of 1.5m-4m, which is a big range. I assume that is to allow for the dynamic pressures mentioned above.

- W

 

[john_morris_uk]

Which means that if you hit a rock and sink in shallow water it probably won't work at all!
What surprises me is that the valise is supposed to float before it inflates. Seems far too heavy. Does my back in every time I heave it on deck.

1. They do float, although I understand your feelings, it just doesn't feel right...

2. If you hit a rock, I guess you will have to hope that you have time to pull the painter out of the liferaft until it gets to the manual inflate mechanism.

Personally, I think if you are on the rocks and worried about the boat not sinking far enough to set off the liferaft automatically, then you might be worrying about the wrong things. How long do you think the liferaft will last as its is washed about in the waves breaking on the rocks?

 

[KellysEye]

>Bigger issue in a knockdown is often the safety gear getting washed overboard. (Personal experience.) Anything on deck becomes sacrificial.

You don't even need a knock down. We were taking big waves over the deck and one night a water and a diesel container were washed off the boat, both were well tied down. Later we had a life ring and light torn off.

On the subject of hydrostatic devices we were woken up one night in Trindad when the Marine police arrived at the boat next to us. Heavy rain had triggered his EPIRB.

 

[Tranona]

While in theory hydrostatic release devices seem a good idea, I have yet to see any reports of them being deployed for real from a leisure boat (does not mean there have not been cases, just none recorded in official reports). So it is difficult to assess whether they are of any use.

 

[prv]

While in theory hydrostatic release devices seem a good idea, I have yet to see any reports of them being deployed for real from a leisure boat (does not mean there have not been cases, just none recorded in official reports). So it is difficult to assess whether they are of any use.

I don't follow the reports as thoroughly as you do, but I did read the one about the two fishing boats with unmanned wheelhouses colliding, that was posted here the other day. On the boat that sank, the liferaft and EPIRB are reported as appearing on the surface shortly after the sinking. In this instance the fisherman had already been taken off by the other boat, but if he had been in the water I'm sure the liferaft's appearance would have been of great benefit.

Not a leisure boat, but the accident could have happened to any small vessel with the same outcome.

Pete

 

[Tranona]

Have not followed the fishing boat reports as closely as the leisure ones, but just looking at the list of reports, there have been over 50 cases of fishing boats foundering in the last 15 years or so, roughly half of them through capsizing. This is almost 3 times the number of founderings of leisure boats over the same period.

One can see the intrinsic value of having hydrostatic releases on boats that are prone to capsize and there may well be cases where they have worked and lives have been saved - guess I will have to bite the bullet sometime and read all the reports to see!

However, if you read all the yacht foundering incidents there is only arguably one where a hydrostatic release might have proved useful. There is speculation that a liferaft with a hydrostatic release might have changed the outcome in the Ouzo foundering, but this seems to be based just on the evidence that the crew survived the collision and assumes that they would have been able to find and board the raft (and of course that it had actually inflated).