making a boat unsinkable.

[chrishelen]

Has anyone used 2 part polyurethane foam in their boat to keep it afloat if it gets holed? I need 2.5 cubic metres in mine. I need to put it under the decks in the void spaces, I plan to put it into tough plastic bags to stop it sticking to the boat.
Can anyone offer any advice before I start please?

 

[Deleted member 36384]

Roger Taylor, the guy thats sails single handed and author of various books on simple sailing does this. He describes the process in his books and I believe (but cold be wrong) on his web pages as well. It's part of his preparation for the long voyages. He packs the forecabin, or a stern area and then seals the space in to stop the foam breaking loose.

 

[basil421]

Expanding PU foam can produce substantial pessures which have the potential to distort your boat.
In the past I worked for a company which injected PU foam into boats for buoyancy and we found it necessary to put the boat assembly into a pressure mould to prevent distortion.
The larger the foam volume the more pressure is produced.

 

[Downsman]

No personal experience, but I have seen an old dinghy that someone tried to add bouyancy to by using expanding foam. All I would say is be very careful because the expansion power seems to be considerable. Whoever doctored the dinghy got it wrong and split the fibreglass locker/space that they poured the poly mix into. I suppose if there's plenty of room for it to expand it's ok, but I don't really know.

Ha! There you go...see post above..

 

[chrishelen]

Expanding PU foam can produce substantial pessures which have the potential to distort your boat.
In the past I worked for a company which injected PU foam into boats for buoyancy and we found it necessary to put the boat assembly into a pressure mould to prevent distortion.
The larger the foam volume the more pressure is produced.

Thanks, I plan to put it under my decks, I can unscrew these to relieve the pressure and trim the overspills.

 

[dartmoor]

Thanks, I plan to put it under my decks, I can unscrew these to relieve the pressure and trim the overspills.

I would think about it very carefully first. PU foam has many voids and can end up retaining water - which would add weight, and could even accelerate osmosis.

Wisest thing I heard from a boat builder - any boat will sink in some circumstances. Better to concentrate other safety measures imho.

But there are better things than PU foam which are much much more water resistant. PU foam is a building substance really - not a buoyancy device

 

[chrishelen]

Closed cell foam is waterproof.

 

[Tranona]

Not really practical in most cases to retrofit that amount of buoyancy for the reasons already suggested. Those builders who have tried to do it in their designs such as Sadlers and Etap have made two separate hulls, put one inside the other and injected foam between them You need closed cell foam and it is not easy stuff to use, nor does it always fill the voids.

The risk of a boat sinking is very small and as others have said, better to put the effort into avoiding sinking in the first place.

However, if you want emergency buoyancy then perhaps look at inflatable bags activated by gas such as are used on self righting inflatables and RIBs. Or, if as you say you have voids why not have air filled bags made to fill the voids?

 

[JumbleDuck]

Thanks, I plan to put it under my decks, I can unscrew these to relieve the pressure and trim the overspills.

It goes on expanding, with considerable enthusiasm, after it has stopped flowing.

 

[john_morris_uk]

Its not just a question of making the boat unsinkable, its the stability and inhabitability of the boat once its flooded that also matters. Its all about the GZ curve of the boat once its swamped vs the GZ curve when its floating to its lines. In addition, the static and dynamic stability needs to be taken into account in your calculations.

Sorry to be the bearer of negative news, but making a boat unsinkable isn't just a matter of providing positive buoyancy.

 

[Neil]

Does anybody sell inflatable bags that you could take out of a locker and pull the cord and inflate inside the boat - one forecabin-size and another similar to (say) fill a stern quarter berth? would it be enough?

 

[Downsman]

Does anybody sell inflatable bags that you could take out of a locker and pull the cord and inflate inside the boat - one forecabin-size and another similar to (say) fill a stern quarter berth? would it be enough?

Not sure about the size when inflated, but don't some rescue/emergency ribs have an inflatable bag on the stern gantry that inflates if they turn over? Maybe the firm that supplies those would be worth contacting.

 

[JumbleDuck]

Sorry to be the bearer of negative news, but making a boat unsinkable isn't just a matter of providing positive buoyancy.

How do you sink a boat with positive buoyancy?

 

[Lakesailor]

You're all obsessed with not sinking. How many of you have ever sunk? You're insured, I hope. How about concentrating of staying alive instead?

I have thread running on buoyancy on PBO. I am adding very little.

 

[Tranona]

Not sure about the size when inflated, but don't some rescue/emergency ribs have an inflatable bag on the stern gantry that inflates if they turn over? Maybe the firm that supplies those would be worth contacting.

See post #8. Yes you can get them made. Henshaws who made the Tinker used to make them and probably still do.

 

[ningcompoop]

I've done it, in the bow of a little trailer-sailor (Sealord 15/Seafarer 465). There was a 'sealed' foam-filled compartment in the bow (and another under the deck), I cut a 8" hole in it, with a view to fitting some watertight storage, and found the foam to be quite soggy - I think from 20-odd years of rain leaking in through the deck fittings. I removed the foam through the hole - this was a hellish job, in the end it would have been much quicker and easier to remove the whole top of the compartment. Refilling it was easy - mixed up the foam in small (100ml?) batches in single-use plastic beakers and (quickly) poured it in. I think I left about 10-15 minutes between each batch to give it time to expand, I also dampened the surface with a plant mister between batches, thishelps promote the reaction. I did it over 2 days, and was surprised how much more it had expanded overnight, so just be careful! You need a warm day, although the foam does produce some heat itself. You also needs lots of ventilation as the fumes are very unpleasant (toxic?). Don't wear your best clothes, do wear long sleeves and disposable gloves. When the foam is set, you can cut it back with a knife/breadknife/hacksaw blade and glass over it.

As far as flotation went, It worked fine; I had to leave the boat on a mooring over one of our particularly bad winters a few years ago, the cockpit drain blocked and the cockpit and cabin flooded during a really heavy downpour. It didn't do the boat any good, but it didn't sink!

(Edit) Just re-read the first post - 2.5 m3 is a lot of space and a LOT of foam! I think I did about 80 litres. It may be easier, and cheaper, to get it done professionally - something like this?

http://www.youtube.com/watch?v=473A8ocG4ok

 

[john_morris_uk]

Perhaps I wasn't explicit enough in my last post.

Assuming you manage to fill some spaces with foam and assuming that the so called 'closed cell foam' doesn't get waterlogged, what makes you think that the boat will float the right way up if it ever floods? You might end up with a boat that's upside down and just a danger to you and other vessels.

I will repeat a little of what I said before: making a boat unsinkable isn't just about making sure it stays afloat. How the boat will behave when its flooded is almost just as important if the 'unsinkable' tag is going to mean anything. Otherwise you are just using up storage space on board to no good affect.

If you are really worried about sinking buy a liferaft and fit it in a cradle with auto-release.

 

[chrishelen]

Perhaps I wasn't explicit enough in my last post.

Assuming you manage to fill some spaces with foam and assuming that the so called 'closed cell foam' doesn't get waterlogged, what makes you think that the boat will float the right way up if it ever floods? You might end up with a boat that's upside down and just a danger to you and other vessels.

I will repeat a little of what I said before: making a boat unsinkable isn't just about making sure it stays afloat. How the boat will behave when its flooded is almost just as important if the 'unsinkable' tag is going to mean anything. Otherwise you are just using up storage space on board to no good affect.

If you are really worried about sinking buy a liferaft and fit it in a cradle with auto-release.

Done that, got a liferaft, got the teeshirt... I need to at least go through the motions of sealing my decks in able to get my MCA code, the mecal survayor is quite straight down the line on this one.

 

[chrishelen]

See post #8. Yes you can get them made. Henshaws who made the Tinker used to make them and probably still do.

Contacted them,put on the back burner u til I have explored every other avenue due to the hellishly expense options they quoted.
But thanks for the link.

 

[FishyInverness]

Holt Buoyancy Bags might be a simpler answer.

I do recall, when I worked for the importer of Pioner boats, the boat sales manager used to cut open the Pioner Multis for certain fit-outs, fill the inside of the hull with a load of small, 1/2ltr plastic screw cap bottles and then re-weld the hull for added buoyancy in certain applications.