Collision damage repair

[Lulworth]

Kind Folks,

As usual, my kid's boat (pictured below before the incident) was the only woodie in a fleet of 300 boats at a recent regatta. It's much loved by it's owner so imagine the tears when my daughter asserted her rights over a port tack boat and, too late, realized that evasive action was required. The tears, of course, were mine back on shore when I peeled off the duct tape jury rig repair job and I saw for the first time the 2" diameter hole (it looks like it was hit with a hammer!) in the occume side. Repairing this while preserving the aesthetics and performance of the boat is going to be a hassle. I'm planning on using a step scarf cut into the side with a router -- that's the theory anyway but fittting the replacement piece and not ending up with a flat spot is going to be a job. Any ideas?

David

http://www.imagestation.com/picture/sraid216/p879c22cc63bc483f7a2129135d4f7e13/ec919ade.jpg

[Stiletto]

I've gone the step scarf route before with plywood repairs, and been happy with the results. If the hole is about the size of a hammerhead, the outer area of your patch would need to be about twice that diameter in my opinion (so a decent lap is achieved) The inner part of the patch only needs to be as big as the cleaned up hole unless fitting a larger panel will provide a neater job.

Fortunately the optimist panels are relatively flat, so a little fairing on the outside should leave a blemish free hull surface. On larger patches, having first routed the lap, I have left the ply supported at each end with a weight in the middle for a couple of days, to closer approximate the curvature in the hull.
Good luck!

[Wild Wassa]

I don't step the faces of a scarf, I make them continuous. It gives the 3mm ply more flexiblity over a small areas which allows the patch to take up any curved shape a tad easier. Weights or battens helps of course. With small patches I shape the female scarfs with a Dremel using a sanding band (like a #432) then cut the hard edges with a chisel.

It is a very small hole. You have the luxury of the paint on the outer hull to hide the largest side of the patch after fairing.

Warren.

[Stiletto]

When Lulworth said a stepped scarf, I took it to mean one lap, as opposed to an angle cut that is difficult to locate with accuracy.

[Bob Cleek]

If it's the size of a hammer head, you might consider cutting out the damaged portion with a hole saw and then epoxying in a plug of the same diameter, but thicker than the hull material. Then sand the plug fair and flush to the hull and seal with CPES and repaint.

[pipefitter]

If you have to follow a curve,you can sand thin the plug to slightly subsurface and fill the rest of the way with epoxy to slightly above surface because it is easier to fair epoxy than it is wood without as much effect on the surrounding area.

[Lulworth]

Thanks for the input. The area that has to be replaced is in total about 2" in diameter with a 1 inch hole where it broke through and about 1 inch of surrounding damaged ply -- I really need a scarf connection on four sides or a circular shallow tapered hole.

A filled straight hole saw cut wouldn't be stable enough and the stiffness of the structure would suffer (slightly) which won't do since the hole is right below where my 11 year old torques the boat flat and up over the waves.

In a boat shop I once saw a tapered grinder thing that was a cone shaped with a 8:1 slope that was used for repairing through-hull holes. It made a taper by just centering the cone in the hole and grinding away (in fiberglass). Something like that would be perfect for this 1/4 thick ply.

In fact a smooth tapered scarf would be ideal (and is the way I do it when joining two pieces of ply on the bench) but here there is no way to get a plane in through the hole and the four sided scarf is probably impossible by hand. ... Well .... maybe with a bull-nose plane and some luck a four sided taper could be hacked out -- I've cut gains in a lapstrake boat that way but this would be much harder.

This brings me back to routing a series of terraces (hence the (mis)use of the word stepped scarf) but it's still not clear how I will be able to do it since there is a gunnel (glued-in like everything else) in the way of the router base so I'd have to use a thick pattern guide to raise the base over the gunnel. Four 1/16 steps routed into the hull panel 0.5 inches or so wide per terrace ... maybe, just maybe ...

Hmmm, this is going to be worse -- either uglier or more challenging or both -- than I thought! Thanks for the ideas and allowing me to think out loud!

David

[Wild Wassa]

Well, I'll think out loud too then.

" ... but here there is no way to get a plane in through the hole and the four sided scarf is probably impossible by hand."

That's why I suggested using a Dremel. After cutting out the broken bit (to a square or rectangular shape so that the scarfing ratio can be drawn parallel) grind it out to roughly the shape of ths slope. Use a file to nearly get the slopes and the valleys perfect and then use a tungsten carbide scraper (rather than a chisel) to fine finish the shape. The patch, you would shape using a plane, so that your join is unassailable ... and the boat sailable.

Mate you are only looking at 30 minutes work max, before the new section is ready to be fitted ... and only 30 minutes because you stopped to have a few adult beverages. If you want to save time, have them before you start working.

Following the other options suggested by Forumites, here is another option. You could even fill the hole with epoxy and sawdust made from the timber taken from the break, just add a pinch of pine sanding dust to lighten the mix so that it becomes almost invisible. Use some fibreglass cloth to give a bit of stability to the epoxy mix. If you do follow this advice. Shape the epoxy while it is still bit soft, put masking tape over the epoxy and use a small block of timber to help shape the epoxy ... don't wait until it hardens before you sand it, epoxy and sanding dust can be like concrete.

Warren.

[pipefitter]

There is another way and it's a rabbet patch. It consists of using 2 different sized hole saws.First using a larger by ¼" hole saw going halfway thru the ply which leaves a ring. Then the smaller saw is used thru the same pilot hole to cut all the way through.The outer ringed area is removed with a sharp chisel and the patch is made the opposite way. Cut half way thru the ply patch with the smaller hole saw and then thru with the larger one. You end up with mating rabbeted circles with just enough room for a good amount of thickened epoxy. If you have a drill press,you dont need the pilot hole for the patch piece. Just remove the pilot bit from the hole saw. It's one of those satisfying to do repairs.

[BFR]

As above work with laps that way you can keep things fair a scarf is gonnar be more truble then it's worth.
if your worried about the strength in a lap joint well don't... it's a opti there isn't gonnar be jack all stress on it... i've seen car bog (bondo) used to fix a hull after it was droped and cracked round the center case.
I rebuilt the bow of a spencer design useing that method once it works a treat simple quick and easy.

[Wild Wassa]

BFR a good and timely post. That's what I'm doing at the moment. Digging and grinding out car bog that shrunk and separated from the boat, very well timed. That is exactly what I'm doing ... or I will be again, when I finish this post.

Don't overlook that the inside of the hull on the Opti is bright and it could be that the boat's visual appearance is important if the break is visible.

What colour is your car bog? It is pink on the boat that I'm doing ... the green stuff I've seen, is even wilder. The grey stuff is perfect for battleships.

Warren.

[BFR]

AHHHHH car bog the wonder gunk... the maker of coves.... the bain of plywood boats.
Had to almost rebuild an entire cocpit because someone had been handy with the car bog.
when I first started my apprentership the company I worked for just about faired up an entire boat in car bog.
but the best use of car bog has to be in an outboard.... I kid you not the bore was badly scored and it wouldn't hold compression so... in went a skim of bog and the bugger ran..... and quickly got traded in.
Personally pink is the colour prefered round here.


I had not noticed the inside of the boat was finished bright..... maybe a battle scar one the other side to even it up???

[pipefitter]

For bright finished ply, the circle method can still be used but on the interior,remove an irregularlycut and grained piece of the surface veneer beyond the area of the repair and match in a new one.Times like these when it is a wisdom to have saved some of the drops from the original panels.If not,just find a close match of like veneer. Presto in the form of a little creative marquetry.

[Lulworth]

Fantastic! The concentric hole saw holes idea is perfect and just what is called for - maybe three steps instead of 2 and a sharp chisel to peel off layers. Now I see it and it looks (in my mind's eye) a heck of a lot better than "boat bog"!

As for the entire repair taking 30 minutes, I'll just say thay it might take you 30 minutes Mr Wasa, but I'm no Mr Wasa! In addition to adult beverages, there's the fretting about screwing up!

Thanks for all the ideas, of course the filler piece is varnished on the inside and will stand out since the Occume has darkened over the course of a summer's worth of sailing but that will serve as a reminder to my little sailor that at some point you have to temporarily conceed the point even when you have the right of way. Next lesson will be in speaking in an angry voice to deter the scofflaws.

[pipefitter]

If you want to keep the repair smaller,you can clean up the damage and glue in a central temporary patch in which to accomodate the pilot bit of the hole saw. Otherwise,you will have to use the solid wood slightly outside the hole for he pilot bit and a larger set of hole saws. Just a thought.