I just bought a used Hemlock Kestrel from the original owner. The hull exterior is not smooth – in many areas the weave is not filled, and there are lots of pinholes. The owner said that she had asked the builder to make it “as light as you possibly can”, and so he tried a different layup than his standard. The finish is very nice just below the gunwales – where resin would sag as it was curing inverted – so I suspect the bottom and chine area ended up resin-starved in the attempt to save weight. It was a success in that regard – the canoe is a few pounds lighter than a stock Kestrel, and was paddled for years with no structural problems.
I’d like to make the hull surface smoother, but don’t know the best approach. I’m ok with adding a bit of weight in the process.
I can think of two options:
Add epoxy resin to fill the weave. My big concern is adhesion – the hull was painted and waxed. Aggressive sanding is out because it would immediately cut into the cloth. I’d have to use a solvent (acetone?) and light sanding to prep the surface.
Use a lightweight filler. I’m thinking of an epoxy/microballoon filler, such as System Three Quick Fair. Faster build, less weight, and easier sanding than straight resin.
I would prime & paint for a finish coat either way.
skin coated hull? I have been told that Dave is often reluctant to build non-gel coated boats but will sometimes be persuaded to do so on special order. I would assume that the exterior cloth layers are still going to be fiberglass, either E 'glass, or more likely S 'glass since the buyer wanted the lightest possible hull.
Since you plan to coat the hull with epoxy anyway, and you want the smoothest possible hull, I would not be reluctant to wet sand the boat until you start to see some dry fiberglass fibers. You don’t want to cut through the outer 'glass fabric layer, but you should be able to see when you have started to expose the fibers without cutting through them accidentally. You should be able to sand out a lot of the bottom scratches.
If the hull is gel coated and you have the time, I would wet sand off a good deal of the gel coat to lighten the boat and smooth it out as well. Waterproof paper of around 180 grit should work. Again, I would continue until you clearly see the weave of the 'glass fibers. I think sanding and a thorough washing, first with soap and water, then with a solvent, should remove surface contaminants and wax.
I have used West Systems 105 resin, usually with 206 hardener, on my Hemlock canoe and it bonds to the vinylester resin that Dave uses just fine. I have generally used West’s 410 microlight filler as a fairing compound rather than West 407 or some other microballoon filler. The microballoon fillers will cure to a reddish brown color which might be harder to cover if you intend to use a light colored paint. On the other hand, West Systems cautions against using 410 filler under dark paint, so your color choice might make a difference. I think any decent fairing compound should help smooth out the surface and fill the pinholes. I would imagine the System 3 products would work fine as well.
..... just check around your area for a shop that has a media blaster and ask them how much to strip the hull .
After the hull is stripped consider using 3M Premium Vinylester filler to fair out the hull .
You can even spray on some gelcoat (a finishing gelcoat) here and there , sand it to smooth ... use it as a "thin" filler fairing method . The disposable Prevall sprayers (also found in hobby RC shops) do a good job of spraying a gelcoat for the purpose mentioned above . Thin the gelcoat for spraying .
If you really want a nice hard decent servicable finish on your hull , consider using an air compressor and a pot spray gun with proper nozzel to apply (spray) a new gelcoat finish all over the hull ... a painted hull will just get all scratched up an marred quickly . Paint isn't hard enough , gelcoat is !
I wouldn't waste the time , effort or expense to prep and use paint as a finish on a hull ... but to use gelcoat as the finish , now you've got something worth doing and working for .
Buy this and spray on gelcoat INSTEAD of paint ...