View Full Version : Keel and Bilge Design Question - Wet or Dry?

10-15-2019, 08:42 PM
I am at this bare-hull stage on my Glastron GT150 restore and have a question that I've been pondering....I'd love to know your thoughts and welcome debates for and against each proposal -

First is what I'll call a "wet keel and bilge area" boat. This has the entire floor filled with 4lb closed cell US Coast Guard approved foam (US Composites) but with 1" voids for water drainage to the bilge area. After glassing in all of the White Oak keel and stringers, then the knee braces, I used construction foam board insulation (white) to create the voids between the foam along the entire keel area and at the transom. After pouring the 4lb closed-cell foam and it's cure, I dug-out all of the white construction board foam. This left the keel area and the voids up the length of the hull with a means of draining to the bilge. The logic in this method was that "if" the foam ever absorbed water, gravity would allow it to drain to the back and go out the drain or bilge pump. The 4 lb foam gave plenty of support for fiberglass floor and is not supposed to ever saturate (US Coast Guard approved) - unlike and much better than that used in almost every old boat we've dug into.

Second, is what I call a "Dry keel" wherein I would completely seal the hull and keel area then fill with the same 4lb closed-cell foam. I would then create a "bilge box" of say 14" wide and 12" long that exposes the hull at the rear to the drain plug and of course have a 1000 gph automatic pump installed at hull level. This would mean that all rain water and any splash or swim water coming into the boat is forced into the box (lowest point in the boat) where the pump would remove it.

Thanks, Gordon

Here in order - inspiration for the "wet keel/bilge area" design; my first "wet keel/bilge area" build ; my current Glastron GT150 hull


Dave S
10-15-2019, 08:59 PM
So the white is foam that you will dig out? What wood are the stringers ?

10-15-2019, 09:30 PM
Dave, yes I dug-out the white board foam with a flat screwdriver. Those are all White Oak. I have a local supplier that keeps it in-stock. It's been used for 1,000 years because it does not absorb water - the capillaries are closed. I've only done the 1 "wet keel/bilge area" boat. My last 3 have all been "dry keel" with a bilge box sunken to hull level in the rear. - Here are several build photos of the 3 boats my neighbor and I built in the last 2 years. The first row is my 1976 Arrowglass/70 Johnson, one we did for his uncle - a 1971 Astroglass/50 Johnson, and finally my neighbor's own 1971 Arrowglass/70 Evinrude (in process). The Glastron GT is the newest project boat - we have 2 going on at once. Gordon


10-15-2019, 09:41 PM
Dave, here is a close-up of the foam and voids along with the bilge pump base epoxied onto the hull floor. In this case, I did not create a bilge box.