Has anybody any experience / knowledge of filling a boyancy compartment in a fiberglass boat with builders insulating foam
My dad in law has an ageing fiberglass boat with a "false floor" flotation compartment. There is a wee bung in it to release water which may have gathered......this now spews out gallons when opened after a day on the water. He put on a new keel because that was considered to be the fault but there has been no improvement If there is a leek in the hull below this floor compartment we can't find it...haven't tried that hard to be honest though) I thought injecting foam into the compartment would resolve the problem and also make the boat safer in the event of being holed below that compartment anyway...........any ideas / knowledge out there?? I've tried a few "marine" forums but there's not much helpful / positive info.

Hi there,

From what I've heard builders foam breaks down after a while when submerged in water. There is a product out there which can be used for what you need to do (can't think of the name of it). A few boys on the Corrib have done this and as far as I,m aware Basil Shields uses it if you want to contact him about the stuff. Failing that PM me and I will try and get you the name of it.

buzzr

The product is a marine buoyancy expanding foam, and amrine chandlers sell it.
Mix two chemicals and inject.
The difficulty you will come across in using it is the possibility of getting quantities incorrect, and forcing the twin hulls apart, which would cause cracks and a weakened structure.
There is also the point that you are going to increase the boat's weight, and alter it's performance, or the power requirements to get at various speeds.

The polyester fibreglass modern lake boats are made of is not a waterproof fibreglass. So it requires protective coating layers. The glossy outside layer is called gel coat.
I would look at the gelcoat, chip off the damaged areas, and sand down and paint on a fresh gelcoat for a permanent high strength solution.
For a shorter term low strength solution, fill, and paint the boat.

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Norm

Float Tube Fishing 30+ years
Float Tubing Info Resource

Thanks for the replies...........very helpful indeed. I had thought of turning the boat upside down and filling the cavity with smoke?? If there were any significant cracks / pin holes they might be seen issuing smoke ?? Just a desperate idea!! However, filling the void with foam would make a good job if I couldn't track down the leak and seal it / them. The water is getting in at the rate of about 3 or 4 gallons over a few hours ? Hard to say, but it certainly does run out of the cavity when I remove its bung at a serious rate! It is also a major safety problem....the only flotation compartment is full of water I'm buying a new boat, but it seems a shame to decomission this one if there is a "simple" fix........thanks again gentlemen for your help.

Not knowing the size of the boat, but one way or the other that's a heck of a leak(s). Depending upon how large/heavy the boat is, is it possible to put same up on a stand of some sort (saw horses as an example), add water and see where it 'comes out?'

fae

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"The problems we face today are there because the people who work for a
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Fred's suggestion is a good one.
A similar idea would be to get a trailer, and after a few hours on the water (to fill in between the hulls sufficiently) haul it out on the trailer, and observe where the bilge water comes from.

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Norm

Float Tube Fishing 30+ years
Float Tubing Info Resource

I get the impression that none of you have used the damnable foam-in-place-two-part-polyurethane.

I have.

I've seen the effin stuff sink in use.
I've seen the foam reaction exotherm destroy a brand new boat.

Adding Expanding Foam Floation - The WoodenBoat Forum

Funny story - and possibly true


N.B. Finding leaks by filling the boat with water can be very misleading - the pressure is acting in the opposite direction.

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Plusnet/Madasafish > Liars to the internet community

Hi.....i am a boatbuilder by trade....and i would be fairly certain that the 'leak' is occurring through the keel fastenings....you said that you have had the keel replaced...so i am assuming that it is probably a timber keel, and probably has a galvanised keel band. if there is no actual 'hatch' to let you get below the false floor....then the new keel has been 'blind fastened' from below, as was probably the original keel

A rather daunting job....but not in any way hard to do....is to cut a couple of hatches into the false floor, then remove, and refit the keel using bolts with large galvanised plate washers and nuts where the keel bolts comes through the hull....using plenty marine type 'mastic' sealer between the keel and the hull, and below the plate washers, on the inside of the hull.....the idea of cutting the hatches is to allow you 'access' to be able to tighten the nuts on the keel bolts.

then either....glass tape the hatches in the false floor back in.....or use a timber 'bead'.....say 40 to 50 mm wide to cover the joints between the hatches and the deck, with a neoprene sealing strip of say 3/4 mm thick below the timber bead....and screw the hatches back down....which will give you access below the 'false floor in case of any further problems.

if i can be of any further help, please feel free to pm me.


regards

Brian

I should have added.....that cutting a couple of hatches in the 'false' floor will do very little to affect the structural integrity of the boat...the hatches need not be wide....maybe 150mm wide.....but sufficently long enough to get your arm into, so that you can tighten the keel bolt nuts......i do not know how long the boat is....so it maybe means even cutting more than 2 hatches.

Thanks Lochan...........that sounds like sound advice to me. Coincidently, I'm having another boat built (19 feet) and discussed this with the builder today. He thinks like yourself (surprise surprise and reckons just cutting out the floor and re-keeling (then reflooring) is the answer. I think your point about "blind" work on the new keel by the last person is more than likely the cause...even though he has a reputation for being very thorough. He just used long brass screws and lots of gooey stuff!! The bolts sound the bussiness, well sealed on BOTH sides. Thanks again Lochan.....Ilike your advice and the logic to it