pour in place foam

[cattrax]

I acquired a fiberglass surf ski and am thinking of making some modifications. First of all a competitive surf ski is very light and is (I think) about one layer of cloth thick. Anyway, there are plenty of gel coat cracks and the hull and deck oil-cans plenty. I am thinking of just filling it up with pour in place foam. I was thinking of drilling a number of 1" holes in the top of the deck from stem to stern so that I would not blow the boat apart. Also making many smaller pours. My intent is to stiffen the hull and deck up and maybe also act to anchor a support structure for a couple outriggers. Am I being realistic on what the foam can do in this situation and if so, what density would be appropriate for this situation. Regards, Cattrax

[Rick Willoughby]

There are probably better ways. Filling it with foam will make it much more difficult to handle. The lowest density two part foam that will not readily absorb water is around 50kg per Cu.m. Does not sound much but wait till you put it inside the hull.

Weigh the hull now with it completely dry, work out the total volume and do a weight estimate based on 50kg per Cu.m for the foam. For a test find some steel weights that match the estimated weight of the foam and tape to the ski. Now see how much harder it is to throw around.

Possibly the best way to stiffen up is with some carbon fibre tape placed sparingly in the locations of flex. It needs some engineering. Tape supplier could probably give advice on where to place it for for best results. This will involve removing gel coat and then fairing and recoating where you apply the tape.

If you want to do a good job you could separate the deck from the hull and use some rigid polystyrene foam sheet at bulkheads.

The utility of the ski will be dramaitcally reduced if it becomes heavy and hard to handle. I find about 20kg is my comfortable limit but then I am not that young and of average build. It is the combination of weight and length that makes it awkward.

Rick W

[robherc]

hmmm...50kg/sqm?? really, if I figure 2lb/sqft. times 27, I get only 54lbs per square yard...that's about 1/2 the density....and it's for Coast Guard approved 2-part epoxy foam. Still has weight to it, but not nearly that much.

other than that, I con't give much input, though, as I prefer to sail/row...so at surfski speeds the handling will be a WHOLE diff. "ball of wax" than what I'm used to!

[Rick Willoughby]

Originally Posted by robherc

hmmm...50kg/sqm?? really, if I figure 2lb/sqft. times 27, I get only 54lbs per square yard...that's about 1/2 the density....and it's for Coast Guard approved 2-part epoxy foam. Still has weight to it, but not nearly that much.

other than that, I con't give much input, though, as I prefer to sail/row...so at surfski speeds the handling will be a WHOLE diff. "ball of wax" than what I'm used to!

Need to work in cubic measurement not square.

There are 35Cu.ft per Cu.m. So 2lb/Cu.ft is equivalent to 70lb/Cu.m or 32kg/Cu.m.

This is what can be achieved with rigid EPS in factory production but I have not been able to replicate this in a sealed situation so I have made some allowance for what I think will be a realistic number.

If you have something that weighs 15kg it is easy to throw it around. Carry it under one arm. Carry on the shoulder. Taking it to 20kg makes a significant difference to portability. Now much harder to carry under one arm. Can be a struggle to throw on the shoulder unless you do a bit of weight lifting. Might be easier for a younger person but there will be a point where the ease of handling is reduced significantly for a small increase in weight. From my experience filling a single person hull with foam pushes it over that acceptable weight point.

Rick W