FOAM BUOYANCY

[Guest]

I need to fit some permanent Buoyancy to a 23' yacht that I am building, can anyone help me in how to work out how much Foam is required to allow a boat to float when full of water, also what would be the best foam to use and where could I get it from. Thanks for your help.

 

[Guest]

Hi
In the Glenans Manual of Sailing there is a section about how to work out the amount of positive bouyancy required to keep a boat afloat. Apparently the standard expanding foam as supplied by DIY stores is not suitable for this purpose. there were some previous postings about this subject here, cant remember how long ago. contact me if you can't find a copy of Glenans.
Regards
Malc

 

[vyv_cox]

This job is verging on impossible for the amateur. The PU foams used for positive buoyancy in Etap, Sadler, etc are closed cell engineering foams. They have considerable health hazards and need to be applied under controlled conditions with specialist equipment. The type of two pack foams that are available from the likes of Glasplies and Strand Glass are far from 100% closed cell, and therefore insufficiently waterproof. I can vouch for the fact that they become saturated with water after a time, having chipped lots of it from canoes some years ago. The single pack foams that can be bought from DIY shops are useless in this respect.

You would find it pretty difficult to retro-fill an existing boat. The production boats with buoyancy have carefully designed inner skins to contain the foam. I'm not sure it would be possible to apply anything like this to an existing boat without losing all the stowage.

I suggest that you would be much better off with either foamed polystyrene, polyethylene or air bags, all widely used in canoes for the best reasons - neither absorbs water and both are light in weight.

To calculate the amount needed, take the displacement, add a factor for buoyancy, say 20%(?) and this is the volume of air needed. 1 ton = 1 cubic metre. I guess polystyrene is something like 95% air, polyethylene and PU probably 80 - 90 % air so you need to factor these in also.