Plywood boat repairs - Northern Ionian - what have I forgotten?

Zen Zero

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Flying to Thessaloniki next week, Ryan Air with only hand baggage and renting a car to get me to the Ionian coast. The other owner is driving down with his wife, daughter, small grandchildren, a box of bits, a new second-hand mainsail, power tools and a vacuum cleaner. I'm going earlier to get a head start because I have to be back in Rome the following Thursday.

Our boat is old and made of plywood, and if anyone wants to buy it, no offer will be ignored. You're also welcome to borrow it, send me a PM. It has the advantage of being already there in paradise!

Here's what we need to do:
Fix hole in hull - put there by the "yard" who took our money for slipping, storing and refloating last winter and, incredibly, this winter too. The slipping technique involved an ancient Unimog and an HGV trailer modified to suit its new role as a launching trolley. Our poor boat was balanced on wooden blocks on this contraption and rolled down a slipway using the Unimog's brakes, unfortunately the trolley went over a bump and the boat fell off its blocks, a sticky-out bit of trolley went through the hull. I turned up early for my 8am appointment and found my boat half in half out the water stinking of polyester and a sheepish yard hand sheepishly admitting to what had happened - the boss was off sorting something else out while the resin dried but when he came back he assured me he would have told me about it even if I hadn't caught them in the act; and that was the best way of fixing holes in hulls that he knew of - he fixes all his own boats that way (he rents them from a beach not far away during the summer). So to cut a long story short I've got this hole in my boat, forward under the bed at the sharp end and below the waterline, patched Greekly with polyester.

My plan is to sand away the lump of splintered wood and polyester with a belt sander, (with a mask on and a vacuum cleaner sucking for all it's worth), and the area around it up to one hole's width all round, back to bare wood, cut a square of 11mm okume ply 3 times the diameter of the hole and glue it over the hole with epoxy resin inside the hull. On the outside I don't plan to do anything more than fair the polyester and glass repair, fill any dents with epoxy filler and paint over it with white yacht paint and then anti-foul.

The co-owner will want to put a patch of glass cloth and epoxy over the plywood patch on the inside and over the repair on the outside, but I am not convinced of the need to do this.

Once the hole in the hull has been repaired, I'd also like to remove the deck hardware from the starboard side (I did the port side the year before last) and make good any rot with off-cuts of ply and epoxy filler before painting and then bolting everything back on again (the toerail coamings will need screwing). I also need to do a bit of repair to the gunwale aft on the port side by the cockpit. It's all stuff that requires bits of plywood, epoxy and clamps.

We're an hour's drive North of Preveza.

Is there anything I'll need that I can't get in Preveza or Lefkas? Anywhere else in those parts where boaty bits can be acquired?

I've already bought Italian epoxy resin and filler because I'm used to working with it, I know it works and I like it; besides this, by way of material I'm going to need white sealant for when I put the deck hardware back, paint, an assortment of nuts bolts and screws, sanding belts, solvent (acetone), rags, ... what else?

All advice will be gratefully received!

Thanks
 

30boat

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I think you should remove the polyester repair entirely.Polyester resin is a very poor adhesive and not at all suitable for repairs over plywood.Is the hull sheathed?If yes then plug the hole with marine plywood and cover with rovings and epoxy .If not you'll need good quality marine plywood to make a scarphed repair set in thikened epoxy.
 

Zen Zero

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I think you should remove the polyester repair entirely.Polyester resin is a very poor adhesive and not at all suitable for repairs over plywood.Is the hull sheathed?If yes then plug the hole with marine plywood and cover with rovings and epoxy .If not you'll need good quality marine plywood to make a scarphed repair set in thikened epoxy.

I do wholeheartedly agree with you about the polyester. The idea of the patch on the inside of the hull is that this performs the structural part of the repair, leaving a ragged dimple that simply needs to be filled for intuitive fluid dynamic purposes and to stop the end grain of the hull panels from getting soggy. What's the harm in leaving the conglomerate of chopped glass strands, splintered plywood and polyester there and painting over it?
 

30boat

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I do wholeheartedly agree with you about the polyester. The idea of the patch on the inside of the hull is that this performs the structural part of the repair, leaving a ragged dimple that simply needs to be filled for intuitive fluid dynamic purposes and to stop the end grain of the hull panels from getting soggy. What's the harm in leaving the conglomerate of chopped glass strands, splintered plywood and polyester there and painting over it?
As I see it water will eventually find it's way into the end grain and you may have a much bigger problem in your hands.How hard is it to scrape that messy repair and redo it with epoxy?
 

vyv_cox

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You can buy just about anything you might need in Preveza, although it may take a bit of searching. There are chandleries at two of the yards, not sure about Aktio, and suppliers of most timbers and metals in the town. I agree about the polyester, if possible I would replace it with epoxy for a sounder repair.
 

oldharry

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+1 On getting rid of the polyester - its the best way of ensuring water is trapped in the ply to make it rot. If the hull was wet, it wont stick anyway for long. You boatyard boss is getting away with it on hulls which normally sit dried out on the beach, not permanently immersed.

If the damage is on a straight, or reasonably straight part of the hull (i.e there is not much bend in the ply, to do the job properly you should cut away any damaged plywood and bring the hole to a regular (i.e.rectangular) shape. Doing the job properly you should then scarph the edges to at least 4:1 of the thickness of the ply. Shape an insert to match, and glue it in place with epoxy, ensuring there are no voids in the glue. This will (should!) give an 'invisible' repair as strong as the original ply. Most people go belt and braces, and fit a backing piece at least half as big again as the outer edge of the repair patch, again epoxied in place. If there is a heavy curve in the hull, it gets a bit more complicated as you have to build up the repair with thin sheets of play to accommodate the curve.

That is the way a professional boat builder would make this repair. A simpler way, almost as effective, but which must have the backing pad to give it strength is to do the same but have a good butt joint on the edge of the 'patch', which is the way most of us who dont have the skills to make an accurate scarph in plywood sheeting, and is just as strong provided the backing piece is secure. If the hull is already sheathed, then the repair must be sheathed. If not dont sheath the repair with anything - if it lifts at all and allows water to get under it it will destroy the ply.

As mentioned above the fundamental issue is sealing the ply end grains. If water gets in it will cause serious problems later on. I have owned quitea few ply boats over 40 years, and a botched repair below the waterline is always a death knell to an otherwise sound hull.

In any case the yard did the damage they should pay for the repair to be done properly and not botched.
 

nimbusgb

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Decent suppliers of all boaty stuff in Levkas, a good timber yard with a few bits of hardwood. A very good English carpenter, Bob Phelps operates from a unit halfway between Aktio and Levkas. If he can't help you with wooden repairs I don't think anyone can!
 

Zen Zero

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Well, the patch is in place, a rhombus of 9mm marine ply, cut to fit between two longerons, glued in with epoxy resin thickend with thickening powder which has been poured into the hole blanked off with a cling film covered board. Tomorrow i'll sand off any excess from outside, fill any voids and give it all a couple of layers of liquid resin. Not sure abuout applyig glass cloth inside or out. It seems superfluous.
 

30boat

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Well, the patch is in place, a rhombus of 9mm marine ply, cut to fit between two longerons, glued in with epoxy resin thickend with thickening powder which has been poured into the hole blanked off with a cling film covered board. Tomorrow i'll sand off any excess from outside, fill any voids and give it all a couple of layers of liquid resin. Not sure abuout applyig glass cloth inside or out. It seems superfluous.

It seems to me you've done a good repair.Enjoy the sailing now.
 
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