How common is it for boats to be unsinkable? ie. has built in floatation

[preventec47]

If I ever buy any kind of boat I really hope that somehow there is no way it can go to the
bottom even if fully swamped. I assume this would mean sprayed in foam in all the
inaccessable areas... Is this an item that is usually featured when boats are sold and
what kinds of boats usually have this feature ? I would think this might be difficult for
sailboats that have keels weighing thousands of pounds.

For boats that do go to the bottom I would like a long string attached to a floating ball
so we can find it later. the length of the string ( now that I think about it ) need not be
any longer than the depth we are willing to go to retrieve the boat.

 

[Leighb]

From memory the Sadler 29 was built to be unsinkable, possibly also one of the Dufours?

 

[Lucky Duck]

Etap rather than Dufour, I think

 

[RichardS]

If I ever buy any kind of boat I really hope that somehow there is no way it can go to the
bottom even if fully swamped. I assume this would mean sprayed in foam in all the
inaccessable areas... Is this an item that is usually featured when boats are sold and
what kinds of boats usually have this feature ? I would think this might be difficult for
sailboats that have keels weighing thousands of pounds.

For boats that do go to the bottom I would like a long string attached to a floating ball
so we can find it later. the length of the string ( now that I think about it ) need not be
any longer than the depth we are willing to go to retrieve the boat.

No keels weighing thousands of pounds on a catamaran .... which is why they don't sink. You know it makes sense. :encouragement:

Richard

 

[KAL]

No keels weighing thousands of pounds on a catamaran .... which is why they don't sink. You know it makes sense. :encouragement:

Richard

Ah, but you pay the price in extra mooring charges...

Light touch paper and retire to safe distance...

 

[KAL]

Actually, I’d love a sail on a cat one day.

 

[coveman]

All the Etap range are categorised as unsinkable and I think some Sadlers had similar built in foam buoyancy, depending on model and year. The other advantage of this is that they are well insulated so you get very little condensation. The downside is that you lose some stowage space - but I would rather have the unsinkability factor myself.

 

[thinwater]

I've never had a boat that could sink (5 boats over 35 years).

 

[prv]

For boats that do go to the bottom I would like a long string attached to a floating ball
so we can find it later.

The sort of boat that would be worth recovering after a complete sinking (ie, small enough to retrieve without engaging Smit Salvage, and simple enough not to need completely refitting afterwards) is generally equipped with built-in buoyancy anyway.

Our previous yard did use that technique for their pressure-washer, though, in case it ever fell off the pontoons

Pete

 

[vyv_cox]

Sadlers 26, 29 and 34 all unsinkable. The 26 can be sailed when flooded, the other two have less buoyancy but will remain afloat.

 

[Tranona]

Both Sadlers and Etap built "unsinkable" boats for a number of years. The buoyancy mainly consisted of closed cell foam injected between an inner and outer hull moulding plus sealed foam filled areas in the accommodation. Both builders were able to demonstrate their boats would float well above the water if flooded. However as already stated the required volume of foam resulted in a considerable reduction in the usable internal volume. On some models there have been subsequent problems with the integrity of the bond between the inner and outer skins.

AFAIK there have been no real life experiences of any of these boats being holed and then relying on the unsinkability - only the staged demonstrations.

Neither builder has survived, and Sadler's later boats did not use the same method of construction. Not sure that the feature is high on the list of priorities for buyers because reports of sinkings (despite what some people claim) are statistically almost non existent.

The reality is that if there was consumer demand and it was technically feasible to achieve in a simple way that did not result in the negative aspects, builders would offer it - but they don't.

Good article on the subject explaining the physics involved in the Feb 2003 issue of PBO.

 

[vyv_cox]

My photo of a 34 above was the consequence of a collision with a ship. The Dorothy Hackforth, massively holed with a piece about a metre square torn from the port quarter. Subsequently repaired and I believe still afloat.

The really big benefit of foam filling is the insulation it provides. In winter in northern Europe we are almost totally condensation free.

 

[Praxinoscope]

I seem to think that the Titanic was described as unsinkable. If it can sink it will.

 

[Achosenman]

I suppose if you don’t put them on the water, they’re all unsinkable.

 

[mlines]

Boats built for the American leisure market are supposed to have "positive buoyancy"

 

[Sticky Fingers]

Where's Brent when you need his well reasoned input?

 

[Tranona]

Where's Brent when you need his well reasoned input?

Already involved in a similar "discussion" (mostly with me and John Morris) on Scuttlebut. Needless to say he has the solution but of course has no understanding of the physics!

Think its time we gave up on him.

 

[preventec47]

I dont know how prevalent the practice of using composite sandwich with foam core is these days as I seem to recall
that 20 or 30 years ago when it became desirable as the next space age construction technique.... things went well for
a while and then they all started to delaminate. In any case I assume a foam core sandwich boat hull would be extremely
buoyant. I remember the ads back in the 60s I think when the Boston Whaler came out promoting foam based unsinkability in their new fiberglass line of boats.
.

 

[johnalison]

I bought a Sadler 29 in 1987 and although it was built with the same sandwich construction as later boats it was not described as unsinkable at the time. Only about the following year did they advertise the fact and effectively guarantee it. I think that a similar thing happened with the 26, but the 34 was later and always described as unsinkable. My impression is that it is not an important matter for most sailors, though I know someone who bought an Etap 34 because of it.

Survivable collisions or sinkings for other reasons are really not very common, and for many of us there are other risks such as fire or injury which we should be concerned about and taking steps to prevent.

 

[preventec47]

Not sure that the feature is high on the list of priorities for buyers because reports of sinkings (despite what some people claim) are statistically almost non existent.

The reality is that if there was consumer demand and it was technically feasible to achieve in a simple way that did not result in the negative aspects, builders would offer it - but they don't.

Good article on the subject explaining the physics involved in the Feb 2003 issue of PBO.

I have seen some videos of salvage operations where they use big air bladders connected to the sunken boats that they
fill using compressors and hoses. Thinking of a large inflatable life jacket type function whereby someone pulls the
ripcord and a scuba tank fills up a huge balloon. I'm not sure a boat hanging ten feet below the surface would be
much more desirable than sitting on the bottom. It might be better to put the effort into a better life raft with
provisions etc. Also maybe someone could invent a quick release keel on sailboats so when you pull
the lever the keel falls off and sinks to the bottom while the boat floats on its side or upside down.
If the boat was designed to float upside down then the mfgr could install a water proof hatch on the
bottom of the boat for access. You know there would be a big market for that