adding buoyancy foam

**Alker Engineering** · 29-Aug-17, 03:28 PM

I wonder if anyone can give me advice on retro fitting buoyancy foam to a flying fish snapper. My new (old craft, recently acquired by me) craft was built as a "land only" model by Flying Fish for their events business at the time. I'm currently doing a bit of work on it to make it the best it can be and have currently got the engine in bits (another story...) and while I'm waiting for parts would like to do a bit more work on the hull. I'd like to add floatation buoyancy and wonder if anyone has done this before, either with blocks of foam or with expanding polyurethane. If so, any guidance on where to put it and how much would be very much appreciated. Also, should there be drain holes in the bottom of the plenum to let any accumulated water out? I'm very new to this so forgive my current ignorance, but very willing to learn!

**Keith Oakley** · 31-Aug-17, 11:19 AM

Most Fish craft have a 3 inch wide slab of foam (usually Celotex) inside the plenum stuck to the cockpit sides. It's fitted before the planing surfaces go on so you would have to turn the craft upside down, take off at least some of the planing surface to get it in then reseal it with grp. Make sure you stick the foam block in well with either straps or grp, you don't want it floating loose and blocking airflow. Alternatively you could try pouring 2 part foam in through the feedholes so it foams on the bottom triangle of the planing surface. The danger with that is you may get an uneven level and block some of the airflow off.

Marlin craft have sealed planing surfaces and use a bilge pump to clear any water ingress. My craft (similar to a Marlin) has a flooding plenum so there are 4 drainholes, one in each corner of the plenum, so it's self draining but it does mean that water will come in if you stop and float. You have to be confident about the amount of bouyancy in that situation, although to mitigate that I actually use 2 inch foam, grp skinned on both sides, as the planing surface; so its lower down and more immediately in the water.

Keith Oakley