Green Valley Boat Works - Builder's Notes:

Hull Repairs

A customer writes...

Hi Martin,

Couple of questions for you regarding the Kipawa I finished last summer.

Drought conditions in Montana for the past couple of years means low flows in the rivers; combine that with an inability on my part to limit canoeing to just lakes, and you've got a few encounters with rocks and the need for some repair advice. I was hoping to find one of your in-depth articles on your builder's notes page; that not being the case, perhaps you have a ready response to the following questions or can point me to the best reference for repairs.

1. Along either side of the keel line in a couple of places, it appears that some excessive flex has stretched the fiberglass within the epoxy, resulting in a pattern of white dots, but no evidence that the epoxy is cracked. Although unsightly, I assume that this does not need immediate attention. Is that correct? When I do have some time, is there a reasonable fix, or is this just something to live with?

2. In one spot, the epoxy is cracked and there is a short (3 inch) section where it appears that there is is a crack in the wood. Moisture can get under the epoxy - you can see the water move a little when you press on the area. There is no evidence of a crack on the inside of the hull. Again, this is just off the keel line. I assume that this is in need of quicker attention, although I must admit that the crack appeared last summer and I just today investigated closely enough to find that the moisture gets in. Can you recommend a quick fix that keeps me in business through the summer, or do I need to stop now and undertake some serious repair work? Do you have a description handy as to how to go about such a repair?

3. I'm thinking that if I am going to continue to use this canoe on Montana rivers, some added strength along the keel line might be in order. Any thoughts on sanding off the varnish and adding a second layer of glass in that area?

Thanks for your help and advice.


Dear Jim,

Without seeing the pattern of white dots you describe I can't be sure, but it sounds a lot like something I've had happen once or twice. The white dots seem like very tiny blisters about 1/16" or so in size, in an irregular patch with no distinct boundary. The blisters can be felt as little raised bumps, and from up close, they seem to form a pattern that follows the weave of the cloth. If this is what you are seeing, then it is probably not caused by stress on the hull. Instead, what I believe is causing it is that there was slightly too little resin applied to those areas to completely saturate the cloth. When that happens, it looks perfect at first, but once the hull gets out in the sunlight, the heat from the sun makes the tiny bit of air left in between individual strands of the fiberglass expand and push apart the fibers, resulting in the ugly little blisters. (If any of you bona fide fiberglass experts out there has a better explanation for this phenomenon, I'd certainly appreciate you telling me!) To avoid this happening, you need to make sure the cloth is well saturated when you are wetting out the glass. However, to repair it is another story.

First of all, beware that if you jump into a repair as soon as the problem rears its ugly head, you may not be treating all of the areas which are still going to succumb to this scourge. It may be better to let the hull get thoroughly exposed to the conditions before attempting repairs. From what I have seen, this condition doesn't immediately lead to leakage through the fiberglass, so it shouldn't make matters worse to use the boat. Once you actually set about to repair this condition, you'll have to face up to some realities. There's virtually no way that you can make a repair that will be invisible when it's done. At least, I haven't been able to. No matter how carefully you sand away the old fiberglass, even being extremely careful to not actually sand through to the surface of the wood, it is almost impossible to get the fiberglass patch to blend invisibly into the repair without some clouding or discolouration showing somewhere which will tell the close-eyed observer that a repair was made. The hull surface can be perfectly fair with the edges all feathered in beautifully, but it won't look as perfect as original. You'll find that this is also one of those effects that may look perfect in the shop right after you've completed the repair, but these visible traces will begin to show after the hull has again been exposed to the elements. All of this assumes you are skilled enough to sand off the old fiberglass without breaking through to the wood. If the bare wood is actually exposed, that spot will definitely show up as a discoloured splotch.

So, what to do? First, if you are going to attempt such a repair, make sure that the patch you sand off is a large, fairly smooth edged patch or patches that goes a bit beyond the affected area to make sure you got it all. Avoid small irregular patches as that could end up being harder to glass over and looking worse. Next, be prepared with how you are going to deal with the final appearance. If the visible signs of the repair are going to become objectionable to you, perhaps the most effective way to deal with that is to paint the bottom of the hull with a marine enamel as a final step. This can actually look very nice, and can hide all manner of repairs, which would actually simplify the repair itself, since you wouldn't have to worry about breaking through to the wood. If you are going to paint the bottom, it would be a good idea to establish the waterline first, and see if you can contain the repairs to the areas below the waterline.

For painting purposes, the waterline should be an inch or so above your normal fully loaded waterline. Also, since the canoe rarely sits perfectly trim in the water, it will look best if the line curves gently up from the center of the hull towards the ends, by about an inch. On an asymmetric hull such as the Kipawa, the upsweep would be greater at the front than at the stern. You will need to lay this line out very carefully with some pin striping tape, and adjust it until you get it perfect. Start with the tape stuck at one end, and hold three or four feet of tape out at a very shallow angle to the hull, sighting along it so that you can easily see the slightest wobble, and gently lay the tape along the hull, trying to get the smoothest possible line. If your wood strips were laid parallel to the gunwales, they will help guide you. Once you have done one side to the best of your ability, take some reference measurements and recreate the line on the other side of the hull. For a nice look, there should be an additional line between the painted and unpainted parts of the hull. Either, use a line of pinstriping tape in a contrasting colour to cover the edge of the paint, or, use narrow masking tape to create a painted line about 1/4" wide separated from the painted bottom by a gap of about 1/4". Follow the manufacturers recommendations regarding the bottom paint. Keep in mind that most of these paints don't go over top of varnish. Done well, a slick, glossy red bottom on a nice cedarsrtip hull can look terrific, and cover up a lot of woes.

Now, let's talk about your other repair problems. First, if you have any cracks, at least patch them before any more moisture gets in. A really fast repair, like during a trip, might consist of squeezing in some 5 minute epoxy, or even some gell-type crazy glue. If water has gotten in at all though, you could end up with delamination occurring between the glass and the wood, not to mention the wood can start to turn black as it starts to decompose. In that kind of situation, as well as serious holes or dents from bashing into rocks, a more serious repair may be needed. In these cases you'll have to actually replace a piece of the hull. At this point, there's no way to hide the repair except to paint the hull as previously mentioned. However, a neatly done patch can still be reasonably easy on the eyes, and in fact, each patch can tell a story, start a conversation, or recall an adventure.

The basic method goes like this. Draw a very neat oval around the damaged area and cut the area out of the hull entirely, smoothing the edges of the hole as precisely as you can. Then, build up a patch out of cedarstrips over top of the hole, being careful to follow the curve of the hull and lining up the strips precisely with the strips already in the hull. (It's always a good idea to set aside some left over strips when you build a boat in order to have material available for a repair such as this.) Make the patch pieces a fair bit longer than the hole so that they will easily bend to follow the curve of the hull. As you lay these pieces, they will of course be glued edge to edge. You can tape the ends of the pieces to the hull to hold them during this process. Also, you can stretch a rope or similar around the hull on either side of the patch to hold the ends of the short pieces. Once the hole is completely covered and the glue has set, you reach inside the hull, and with a sharp pencil, trace the outline of the hole onto the inside of the patch as carefully as you can. Then remove the patch, and cut carefully to the line. Carefully test fit and sand the edges until the patch fits the hole as precisely as you can. Then, glue the patch into the hole, leaving the raw wood sitting a bit higher than the surrounding surfaces all the way around. Next, sand the patch smooth, feathering into the fiberglass around the hole. For the best appearance, avoid breaking through the original fiberglass and exposing the wood around the edges of the patch. Then, apply the fiberglass over the patch and a few inches beyond all the way around. After the resin has cured, feather sand the 'glass until the hull is smooth and fair over the patch. Repeat the process on the inside of the hull, and finish up with paint or varnish as required.

As for adding a second layer of glass over the entire bottom, yes this can be done, but as mentioned previously, you will be able to see that it's got the extra layer. If the appearance is objectionable, try the painted bottom approach. In general, wood strip and fibergalss construction can be reasonably durable, as well as repairable. In most cases, the methods you use will be determined by the importance of the final finish you want to achieve or preserve.

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Author: Martin P. Step

Copyright 2001

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