Buoyancy foam - what are the options?

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Would value the group's perspective on a little project. I have an older RIB style dinghy with a double floor. The upper floor has some cracks from the boat to bilge, some structural flex around the cracks and I believe water is able to pass through the floor into the bilge area between the upper and the hull. The boat is still able to operated and floats fine even with a bilge full of water, but I would like to figure out a repair to slow/stop any further cracking/deterioration of the floor. If I could get into the bilge, I would add a few supports to prop up the floor from below but looking at an approach that doesnt require cutting out the cracked floor, putting in supports and then re-glassing the whole boat.

My thinking was adding some expanding foam or other additive through the bilge drain hole that would serve as a structural component to support the cracked and slightly sagging floor. If the foam consumed the full area of the bilge that would seem to be an advantage as well from a buoyancy perspective. Not a huge amount of weight that needs to be supported and bilge doesnt have to be 100% waterproof based on current situation.

-What products would be liquid enough to be injected through the bilge garbord plug hole
-Are there products which could provide some structural integrity--the "height" of the bilge is only an inch or two
-Will water flow around the foam or be absorbed by it assuming that I still have cracks that will allow encroachment by water
-Is there a better way to repair this

Thanks in advance for your advice and happy boating to you!

 

Jimjimjim
Welcome to the forum.

All expansion foams absorb water. The expansion foam will NOT flow far from a discreet opening and will expand blocking the opening. Therefore expansion foam will not accomplish your goal.

DO NOT cut the sole(floor) out. You will NOT be able to reinstall it.

Possible solutions
One
Grind off paint/ gelcoat and add several layers of glass to the top of the existing sole.
Two
Grind off paint/galcoat
Bond plywood to existing sole.
Three
Do both and add plywood between layers of glass.

 

@Blueknarr -Thank you for the clarity about how the material--sounds like it doesnt have any of the right characteristics. I don't love the labor to age of boat equation but if it gets any worse that the grind/reglass is the likely path. Figure that the resin will seal the cracks, fill in the low spot and the glass/resin will hopefully provide a bit more structure above to prevent further cave in.

Meanwhile I will keep dreaming of a quick fix that doesn't exist like a balloon that can be inserted and then inflated to pressure to lift the floor.....

 

Intriguing problem that got my imagination working.

My first thought was a coarse threaded fibreglass "screw", like those kitchen cabinet adjustment feet, through a threaded fibreglass "biscuit".




You could pop the "biscuit" through the slot, rotate it to provide interference, and then screw down the coarse thread against the bottom layer.
You could even use a plastic cabinet adjustment leg, to create a mould for the fibreglass "screws".

Then chop the fibreglass screw off level, and epoxy the biscuit and screw solid with the upper layer.

 

Appreciate that you’re activating your brain for my project and love the creativity! Like your biscuit/expander idea and am looking to home improvement as a source of a solution short of a “proper” repair.

I need something like the masts of a ship in a bottle where something mechanical and folded could be slid in and then erected once in the hull.

Or a giant stent.

I’ll fiberglass in the spring if I can’t come up with a “better” solution.