Bottom of hull didn't hold its shape

sluggo · Post by **sluggo** » Sat Apr 11, 2009 10:55 am

While I was scraping the inside of the hull I was running my hands along the outside and noticed that the bottom football portion didn't really hold its shape once removed from the moulds. It's sort dipping in. Granted, a bit of this is probably from my workmanship on the strips when sanding/fairing. But for sure I can press down on the bottom of hull from the inside and the shape seems to be better. I'm thinking that when I go to fiberglass the inside I can place some weight (bag of sand or similar) on the football while the epoxy sets. I'm not sure if that will help though. I've never read of people having this problem before though so it sounds kind of weird to me. Any thoughts?

Jim Dodd · Post by **Jim Dodd** » Sat Apr 11, 2009 8:51 pm

Usually, hulls sag the other way.

What happens when you pull the sides inward ?

You could with really good Duct tape, tape some weight to the underside of the hull, to pull it into shape,that way nothing would hinder glassing the inside. Just a thought !

I've not had this problem !

Good Luck !

Jim

Rick · Post by **Rick** » Sun Apr 12, 2009 8:24 am

Sluggo, turn the canoe over and sight down the keel line... is it hog-backed, that is, is the keel line developing a concave depression, where it should be straight or rockered with a convex curve?

If the keel line is becoming hogged, this can be serious because hogged hulls have poorer hydrodynamics and will paddle inefficiently.

If the keel line may be hogged, stretch a fishing line along it from stem to stem and measure how much hogging there is relative to the straight fishline. If the keel line is still straight amidships, the hogging isn't that serious and probably won't affect performance much. An inch of concave hogging is something that should be corrected if possible... maybe you could tell if there is any hogging in the first place and then decide what to do.

What are you building?

Larry in Champaign · Post by **Larry in Champaign** » Sun Apr 12, 2009 12:24 pm

I used cradles for holding my canoe as well. I cut them 1/2" proud of the station molds to allow for strips and foam compression. I also considered the rocker so that each cradle would fully support the canoe at each station. For a 17' canoe I used four cradles placed at station 3, 6, 10, and 13. I also used spreader strips to maintain the sheer width. I'm wondering if your cadles could be causing the boat to bow up in the middle? Try lifting the ends and see if the dip corrects itself. It looks from your photos that there may be a lack of support towards the ends which may cause your dip. I'm just brainstorming here! Good luck!

Larry

AlanWS · Post by **AlanWS** » Tue Apr 21, 2009 3:32 pm

I would bet that it's humidity. You have glass on the outside that does not expand, and the wood has taken up more water now than it had when the outside was glassed. That causes it to swell, and will tend to flatten out the bottom. If you can warm and dry the air, it may return to its previous shape. In any case, make sure it is the way you want it when you apply the inside glass, even if it takes making some outer curved supports for the hull.

frugal · Post by **frugal** » Tue Apr 21, 2009 7:09 pm

It looks like you have three cradles. I'm just guessing here, but I would bet the problem is in the centre cradle being slightly high (with added foam). Try removing just the centre cradle and see if it corrects itself.

I used slings made of 4" canvas strips. I just had to use spreaders on at least 4 locations to keep it from curving too much as I worked.