Prospector Cruiser Hull Shape

[Oyster Cove]

G'day, I have applied three coats of epoxy (and cloth) to the outside hull of my Cottage Cruiser. The hull design is a shallow arch - not flat. However, after removing the hull from the moulds and then preparing the inside for epoxy, I noted that the hull shape is now flat or even concave in the middle (see photo). What might have caused the hull to loose its original shape (shallow arch) and is there any way to correct it? I do intend to apply a fourth coat of epoxy to the outside hull.

Thanks, Richard

[Cruiser]

Did it do that immediately or over time, how long did it sit off the forms until you noticed the issue?

There are a few bui8lders here that have a broader experience than I do, I hope they have some advice, because that doesn't look good and I have never seen the like.


Brian

[Jim Dodd]

I have in a few instances, had a hull Bulge outwardly, because of too tightly stripped in the middle.
Did you remove the hull from the forms and rest it on something ?

I would start by slipping wedges between the hull and the forms, to gently lift the hull up.

Use several tapered wedges, placed in different spots, so not to create a lot of pressure in one spot.

I might pull the hull from the forms. Set it in a saddle stand, and strap the forms back in place.

Just try and bring it back in shape. Setting in the hot Sun may help stretch it back in place.

Keep us informed !

Good Luck !

Jim

[sedges]

Wow, that is really seriously misshapen. A bunch of questions.

Is that part of the hull flexible?
Can you push it back into shape?
What strip thickness and cloth weight?

The first thing that comes to mind is that when you were fitting the final strips in the bottom they were forced in causing tension in the bottom that caused the hull to adjust when released from the moulds.

If it can be pushed back into shape you might be able to install a wood rib, or ribs to hold it in shape. The rib(s) would not have to go up the sides, just long enough to bridge the bottom. Feather the edges of the rib so you can glass over it when you glass the inside. You need to do the rib(ribs) before you glass, that way the inside glass will help hold the shape permanently. I would make ribs out of cedar so it is light and easy to shape. You can get the shape of the rib from the mould.

[Oyster Cove]

Thanks for your comments. The concave part of the hull is flexible and can be pushed back into its proper shape. The planks are 1/4" WRC and the cloth is 6 ounce using West System 105 and 207. I don't think the centre planks were put under any undue compression or tension.

I am wondering if this is temperature related. I am in Tasmania and it is winter now. I moved the canoe inside the house to do the epoxy work on the outside of the hull. It stayed in the house for at least 72 hours after the resin was applied and temperature was about 20 degrees centigrade. The shape looked good. I then moved it back to the shed where overnight temperatures can be as low as zero centigrade. I noticed the change in hull shape two week after it was moved to the shed. I will bring it inside again and see if the shape improves with the warmth. If not, I will consider installing 3 ribs using the moulds 0 and 2 for shape as you suggest. I will then fibreglass over them when I do the inside of the hull.

[sedges]

I think that is a good option. The ribs can be 1 1/2 to 2 inches wide and maybe 3/8 inch thick. Feather them out before you install them. Doing it in the boat would be a pain. You will want to rig a cross piece across the canoe and cut a piece of wood to length to press the rib into the bottom while the glue sets. All that can be done with clamps and will take some experimentation to set up. It can be done with weights as well, but balancing something heavy on a 2 inch wide rib is dicey.

I have glued ribs into the bottom of glass or royalex canoes that have gotten loose as they get banged around on the river. Its and puzzle for each one, but once installed they do the trick.

Good luck! You have a beautiful hull.

[Oyster Cove]

Good news. The proper shallow-arched shape of my hull has returned. After bringing the hull inside the house and maintaining the temperature at 20 degrees centigrade and installing temporary thwarts, the hull came good after 6 hours. I have now applied the fourth coat. The hull has maintained its shape even after the thwarts were removed. I can only assume that the cold temperature and the different wood in the hull caused the shape distortion while it was off the moulds but not completely fibreglassed. Thanks to everyone for your comments and advice. Cheers, Richard