Flotation/buoyancy

Update:

I’ve decided I’ll keep it simple, and use expanded poly styrene foam sheet for flotation.   This is the sheet pink stuff used for building insulation.   Installation will mimic the original, except the foam will be secured with expanding foam, the parts will be neatly fitted, and - I think - there will be greater cubic volume. I decided not to encapsulate the  foam as this simply adds weight, and makes future repairs difficult. (It’s also a lot of work.).   As it is installed on the underside of the decking, it is somewhat protected from damage.  The first strategy will be to install as much foam as possible, secured in place on the underside of any decking. We will test the boat the spring and see if it’s sinks!

How much Flotation?

Here is an interesting article on how to calculate the buoyancy required.  

https://www.glen-l.com/weblettr/webletters-7/wl55-flotation.html

I will likely replace the foam with a mixture of sheet styrene from home depot, and poured-in place urethane for the enclosed space up forward.  

Class rules state:

Buoyancy;
	(1) It is not practical fully to test the buoyancy compartments by total immersion owing to their large volume. Officials Owners are to check all watertight joints and satisfy themselves that they are efficient and that the hatches are adequately watertight. In addition, the boat is to be floated in a waterlogged condition, with the water overflowing the top of the centreboard case. After 20 minutes in this condition, the boat is to be bailed out and the tanks inspected for leakage. This test must be carried out annually and the certificate endorsed by a club or class official. Certificates without current endorsements cease to be valid. Additional buoyancy bags apparatus may be carried.
	(2) Mk.1 and Mk.2. G.R.P. boats shall have solid foam buoyancy units permanently fastened to the hull to provide 52 lbs. (23.5 kg) minimum lift in the forward buoyancy compartment, and 58 lbs (26.5 kg) minimum lift in the aft buoyancy compartment. Mk.2. versions shall in addition be fitted with one solid foam buoyancy unit of 50 lbs (23 kg) minimum lift under the side bench on either side
	(3) Mk.3. G.R.P. boats shall have one solid foam buoyancy unit providing 40 lbs (18 kg) minimum lift permanently fitted into each side buoyancy tank and solid foam buoyancy units providing 20 lbs (9 kg) minimum lift permanently fitted forward of the main bulkhead