Unsinkable boats

[ifoxwell]

So it sounds like a good idea but I'm guessing that just means that there is a lot of foam/balsa some where in the make up to provide the buoyancy.

So move forward 20+years is it now such a good idea?

Any small amount of damage, a wobbly stanchion base, a screw thats not sealed and tight and that foam/balsa is just going to be soaking up the water. Ok so you get a survey and he says its ok but is it! and what happens from that point on.

How do you know its all ok?

 

[RichardS]

The main problem with boats is that there is a huge mass of lead or steel trying to drag the whole kaboosh down to meet Davy Jones ....... but there is a type of boat that doesn't have this encumbrance so is easy to make unsinkable.

Richard

 

[[3889]]

Though floating upside down is not always to be preferred

 

[pmagowan]

I don't think you can make a yacht 'sink-proof' but you could certainly make it 'sink resistant'. Watertight bulkheads, floatation chambers, crash bulkheads, double skins etc. I expect that all these things would degrade with poor maintainance in much the same way as every other component on a boat.

 

[Sailorsam101]

I've spent a lot of time on boats with foam cores that are 'unsinkable'. What this means when the boat is 20 years old is leaks inside. When it rains outside and the hull flexs from natural movement water is sucked into holes and taken in by the foam which has no broken up.

This is then squirted out as a slow drip anywhere in the boat making it almost impossible to find the source of the leak. Trust me on this one...a leak through a cockpit screw leaking showed up as a drip in the forepeak..!!!

 

[vyv_cox]

When I fitted Yacht Legs to my Sadler 34 I cut pieces of foam from inside the topsides in order to install backing pads for the sockets. I submerged one of the pieces of foam, about 8 x 6 x 1 inch, in water for around a week. At the end of that time I could detect no absorption of water at all.

There is a small loss of internal space in a Sadler 34 due to the foam but it is surprising how cleverly the buoyancy has been designed. Still plenty of space aboard for two of us for six months per year.

 

[pmagowan]

I've spent a lot of time on boats with foam cores that are 'unsinkable'. What this means when the boat is 20 years old is leaks inside. When it rains outside and the hull flexs from natural movement water is sucked into holes and taken in by the foam which has no broken up.

This is then squirted out as a slow drip anywhere in the boat making it almost impossible to find the source of the leak. Trust me on this one...a leak through a cockpit screw leaking showed up as a drip in the forepeak..!!!

But that just sounds like a badly built and/or maintained boat. If you have 2 skins and a foam core and it leaks into the foam then with a standard construction, without the 2 skins, the boat would just sink. So comparing a boat with a drip with a sunk boat gives a better impression. Of course, it shouldn't get a hole in it unless you don't do routine maintenance. Of course if the original construction was poor then it is just a bad boat. You don't need a foam core to make an 'unsinkable' boat.

 

[25931]

Though floating upside down is not always to be preferred

Not preferred to sinking ?

 

[KellysEye]

Etaps are unsinkable http://www.old.etapyachting.com/

 

[noelex]

I am surprised watertight bulkheads are not offered as an option by more builders. If incorporated into the design stage, the cost is not enormous, especially on large luxury yachts.

Life-rafts are the last ditch solution, but they seem to have a surprisingly poor reliability/performance record.

A couple of large watertight compartments can make sinking unlikely, although fire is still a risk.

 

[ifoxwell]

I submerged one of the pieces of foam, about 8 x 6 x 1 inch, in water for around a week. At the end of that time I could detect no absorption of water at all..

I have no doubt the materials have been carefully selected, but the reason it hasn't absorbed any water is that its a closed cell foam, effectively lots of bubbles of air held together.

But over the years as the foam ages, gets worked as the hull flex'es etc, how many of these bubbles burst..... and then when you factor in voids in make up, poor bonding etc there could be loads of pockets of air just waiting to soak up water?

I hope I'm just being paranoid but it does make you think.

 

[Koeketiene]

I don't think you can make a yacht 'sink-proof' but you could certainly make it 'sink resistant'. Watertight bulkheads, floatation chambers, crash bulkheads, double skins etc. I expect that all these things would degrade with poor maintainance in much the same way as every other component on a boat.

Years ago Etap opened all the seacocks on one of their smaller models and sailed it across the Channel - and back.
IIRC there was a feature of the feat in YM at the time.

PS: Found the YM article - http://www.yachtingmonthly.com/gear/trying-to-sink-an-unsinkable-boat-31338

 

[boatingdave]

I think someone in Belfast may have the plans of an unsinkable ship if anyone is interested?

 

[RichardS]

Years ago Etap opened all the seacocks on one of their smaller models and sailed it across the Channel - and back.
IIRC there was a feature of the feat in YM at the time.

But look at the monohull disasters where the boat is found floating upside down with no keel. It makes me wonder whether most yachts are slightly positive buoyancy because of the amount of wood on board, once the keel has gone.

Could be trapped air as well, but either way it's pretty close to neutral.

Not mobos of course, presumably the engines outweigh everything else, like the keel on a monohull.

Richard

 

[Koeketiene]

But look at the monohull disasters where the boat is found floating upside down with no keel. It makes me wonder whether most yachts are slightly positive buoyancy because of the amount of wood on board, once the keel has gone.

Could be trapped air as well, but either way it's pretty close to neutral.

I suspect it's trapped air.
Not much wood found on boats these days - and all that MDT will desintegrate after a while.

Also, a couple of Vendee boats capsized over the years - all remained afloat. And these boats are pretty bare down below.

Even poor old Bullimore way back in 1997: http://news.bbc.co.uk/onthisday/hi/dates/stories/january/9/newsid_2518000/2518229.stm

 

[rogerthebodger]

Moquini lost its keel in a race 11 years ago and was found subsequently upside down with the rig and sails still intact.
It was constructed of PU foam between 2 layers of GRP in the normal way these days
As found

After the rig was cut away

Being towed in

My 2 friends one lost a son and the other her husband.

http://www.mysailing.com.au/news/possible-sighting-of-south-african-catamaran-reopens-moquini-wounds

 

[vyv_cox]

But over the years as the foam ages, gets worked as the hull flexes etc, how many of these bubbles burst..... and then when you factor in voids in make up, poor bonding etc there could be loads of pockets of air just waiting to soak up water?

Hull flexing? What kind of boat are you sailing? When I tested my foam it was already more than ten years old.

Sadlers 26, 29 and 34 are all foam filled. The 26 can, and has been, sailed when fully flooded. Don't know whether it has been tried with a 29. Photos show a 34 that was in collision with a ship. This was a sea school boat, far from new. Certainly not sailable but at least still afloat. She was rebuilt and I believe still sailing.

 

[Ceirwan]

Hull flexing? What kind of boat are you sailing? When I tested my foam it was already more than ten years old.

Sadlers 26, 29 and 34 are all foam filled. The 26 can, and has been, sailed when fully flooded. Don't know whether it has been tried with a 29. Photos show a 34 that was in collision with a ship. This was a sea school boat, far from new. Certainly not sailable but at least still afloat. She was rebuilt and I believe still sailing.

I suppose its good that its not going to sink within minutes from under you, but that's hardly a habitable boat, it's only the cockpit coamings and coachroof actually above the water.
I'd still be getting into a liferaft than staying on that thing.

 

[pmagowan]

I suppose its good that its not going to sink within minutes from under you, but that's hardly a habitable boat, it's only the cockpit coamings and coachroof actually above the water.
I'd still be getting into a liferaft than staying on that thing.

I suppose its good that its not going to sink within minutes from under you, but that's hardly a habitable boat, it's only the cockpit coamings and coachroof actually above the water.
I'd still be getting into a liferaft than staying on that thing.

But that is the thing, I suspect that a life raft is worse and may only survive a few days. Neither are good but the boat is more likely to be found and its hull will stay in one piece. With watertight bulkheads or floatations chambers it should float even higher. In fact, with a watertight bulkhead only the stern would have flooded to the new waterline. The boat would remain sailable.

 

[Ceirwan]

But that is the thing, I suspect that a life raft is worse and may only survive a few days. Neither are good but the boat is more likely to be found and its hull will stay in one piece. With watertight bulkheads or floatations chambers it should float even higher. In fact, with a watertight bulkhead only the stern would have flooded to the new waterline. The boat would remain sailable.

I totally agree with you that it could be done better. In fact they even sailed that Etap across the channel so I'd be in no hurry to abandon that.

I was talking about this specific example shown in the photos. The thing is completely awash, you're fully exposed to the elements, every passing wave will wash over it, a liferaft will give far better shelter, people have survived a long time in them, it should certainly last more than a few days.

They say you should step up into the liferaft and that looks like a good example of it to me.