Thread: Puncture in plywood hull panel - repair job

I am not a professional, so my advice might not be the best.

With a 2 cm x 2 cm hole, I would put a plywood patch on the inside, then fill the hole from outside with epoxy + filler, sand it smooth, and paint.

Hello Engblom,

This is what I would do if I could access the inside. As I have no access to the inside, I need to make a larger hole (minimum of 10 cm * 10 cm) in order to allow my hands in to fiddle with the inside piece. That seems a bit drastic for a 2 cm * 2 cm problem (the bottom is V-shaped, so the most serious dent is only 1 cm * 1 cm so I was wondering whether there would be an easier and more convenient solution...

What about drilling the damage out with a 19 mm or 22 mm drill bit and then just filling the hole now created with epoxy glue, the boat the right side up, with a piece of plywood with packing tape / non-sticky plastic taped to the hull whilst the glue cures?

Then sanding, epoxy top coat with very light fibre glass, primer and paint.

I was thinking that this size of opening allows you to feel the edges to see whether something more drastic is in place (and if so, proceed with sawing the larger hole).

Anybody having experience in these matters?

Joost

Hi Joost

We had similar damage to a Dabchick once. We made the hole a neat round shape and made a plywood stick that was just wide enough to fit in the hole. drill a hole in the stick and tie a string through the hole so that when you coat the stick with epoxy and poke it into the hole , you can use the string to position it and apply pressure while the epoxy cures. Then just make a plywood patch to fit the hole and glue it in.

The other way is to cut out the hole to a neat shape as before, but you carefully chamfer all the edges with a small rasp. You do the same with the ply patch to make it fit nicely. Chamfering the edges increases the surface area for the epoxy to make a strong bond. The advantage with this method is that the patch can't fall into the hull and after you've applied the epoxy and positioned the patch, you can cover it with grease paper or peel ply and put a weight on it while it cures. If you're careful you can make it absolutely flush so that when it has cured and you peel away the grease paper, the repair is finished.

Thank you Bruce, I think that the first method will be the way to proceed. I will cut a nice small rectangular hole (easier to make the plywood patch later on) and put a plywood stick in it using the method you describe. This would avoid having to open her up further than necessary. Should work nicely I think to make the hull watertight again and to keep any rot at bay in the future. I am sure that I can finish the repair area flush again with the remainder of the plywood.

Now, who has some ideas on the paintjob that the repair requires to make it all look neat again. Is that at all possible without painting the whole hull again (in other words, how do you make the repainted section flow nicely into the old paint job)?

If so, I may opt for a quick and dirty paint job now and only when the season is finished do the whole job.

Howdy ...
If you can't access the back ... perfect ... everything will be hidden. Read all of this so you follow the reasoning!

cut a rectangular hole. I am not being specific about the size as you need to work it out specifically.

Make a patch to fit the hole.

Make a backing ply block - it needs to overlap hole by 30mm. This is a bit weak but use glass on the outside to bring it up to specification.

Now the point of the rectangular hole is that you can put the repair assembly through the hole you have cut in the hull and then rotate it and pull it outwards.

String is not a bad idea ... but I would put a couple of light pieces of timber across on the outside and use the drywall/plasterboard screws to pull the assembly outwards.

If there is any curvature the timber pieces need to line up with the direction of zero curvature so they sit flat.

After use the invisible glass method on this page. Though you could go sailing before you do this step! It is summer after all!!!

Q&A - Specific Methods to Repair, Restore and Paint Wooden and Plywood Boats - Michael Storer Wooden Boat Plans

Hello MIK,

Thank you for the feedback. This thread is especially helpful on the finishing side of the repair:

https://www.woodworkforums.com/f169/h...58/index2.html

Thank you for pointing me to this one! I will probably now go the stage "Patch gloss paint" and will repaint the whole hull later in fall time when the sailing season is finished.

Having read all of your post, I would like to confirm the following:

The hole that I need to cut being very small measuring a maximum of 30 mm * 30 mm or so, it will be difficult to put in a backing block making a 30 mm overlap in all directions. Only in 2 directions will be possible with the backing block going lenghtwise with a 30 mm overlap each way (the chine is in the way on one side). There is not much curvature in this area of the hull and all of it is going lengthwise. Would this be sufficient if using glass on the outside (per the method you describe for the Sabre you once owned making a small dish and filling it will light glass)?

Joost

A repair like this is pretty simple. Lets assume you can't get at one side, as this is the most trying. There are two things you have to do: first is hold the repair in place until the goo cures and second, probably most importantly, make a repair that will not reappear later.

To address the reappearance issue, you should taper the edges of the hole. As big a slope as possible works best. Of course, cut the patching panel with a sympathetic edge treatment. Before inserting it, very lightly ease the feather edges of these tapers. This will proved a place for the goo to live, under the fairing compound, so it can't "circle" out from vibration or other abuse. A feather edge or a crisp edge will in time, seeming to always "project" the outline of the repair, through the fairing compound in places.

As to fitting the piece, without a backer on the inside, the tapered edges help to a degree, but a screw in the middle of the patch piece, just barely inserted, but not punching through can be used as a handle and also to position the piece, as the initial coatings of goo cure. You can make a bridge from some scrap stock and use duct tape to hold things in position. The piece you're installing isn't big enough to warrant much more than some tape, though maybe some blocks of wood, bridging the area (but off the surface) to keep gravity from screwing with it.

Surface treatments after the piece is glued in, have been covered and the advise is all good. You really don't need to have a backer on the inside, for a piece this small. Technically, it might be slightly weaker in this area, but it would need a direct shot on the repair, likely of similar strength to what caused it in the first place, to do any real damage. If this is likely in the future, then a backer may be advised, but for a location that isn't likely to get bashed in regularly, no backer is necessary.

Lastly, and again to avoid the backer, use a thinner repair piece. If the hull is 12 mm, then use a 9 mm repair piece and hollow out the surrounding hull area with a grinder. Glue the patch in so it's below flush, then some cloth and thickened epoxy over lapping, into the hollowed out area, before the fairing compound brings everything up to flush. This is the way I'd do it, as it's fast and I can do all the goo work in one shot, leaving just fairing it down to the surrounding hull surface after everything cures.

Thanks for the detailed advice Paul. Indeed I cannot get to one side of the repair but I believe that I have two workable solutions now: either with a small backer or without one if tapering the edge.

I may just use a small backer due to the thickness of the ply: it is only 5 mm thick and it may just be easier to use the backer although it will mean an extra day to let the glue cure on it.

Normally it is not an area that would get bashed in regularly unless of course I make the same mistake when taking the launching trolley of its trailer.

Joost

Joost, just to add some more info.

Diagram 1 is (I think) what PAR is suggesting. The diagram shows a taper of 5 x ply thickness, but up to 15 x is better (It's not as hard as it sounds)

Diagram 2 is a patch something like what Mik has suggested (ignore the reference to nails though). Where Mik suggests a rectangular hole (so the pre made patch and backing can be passed through diagonally) there are a couple of other variants. If the backing patch has a hole in the middle it is possible to clamp through the hole. IE clamp the backing patch on from outside with a, say 30mm overlap to the hull and also for the patch. When it dries, glue the repair patch in and weight it like diag 1. It is also possible to do this with a round hole if the backing piece has a slot in it as shown in this diag. The backing piece can be fed through the circular hole like one thread of a screw (if that makes sense)

Regards
SWK

REctangular hole for me

I do like PAR's point that the repair can be under specification by a bit because it is unlikely to get a shot in the same place for a second time.

MIK

Thanks for all the advice so far and SWK for posting the clear diagrams and info.

Diagram 1 seems a possible solution, but if going for this solution I will keep it all square as I don't see myself making accurately tapered round filler pieces / holes.

I need to get the boat of the trailer and start working on it I guess. Will try to document this with photos for future reference to other forum users when in a similar spot having to make such a repair.

Joost