Plywood hull and chine repair advice

[EastCoastChris]

I was advised that a replacement panel should be scarphed in, but your operative seems to have used a butt joint.

You can do either, a scarphed repair is invisible, a but joint with a backing piece is a visible repair. If you do a butt joint you must put a backing piece behind the joint and make sure there's plenty of expoxy protecting the end grain of the ply. You can clearly see the backing piece on the transom internal photo.

Either repair is watertight if done correctly, but getting a scarph done is a lot more expensive.

Use top quality marine ply (I requested Robbins Super Elite) and epoxy the end grain of the joint.

The repair wasn't taken back to the stringers, you shouldn't do that the surface area is great enough behind the joint, on the left it's back to a strap behind an original joint and on the right a new backing piece was added.

Chris

 

[Seanick]

A half lap onto the surrounding panel would not have gone amis. Easily cut with a router and no straps req'd. If you were feeling flash you could step it twice, but by the time you had done that you could have pulled out the scarph jig and routed in a scarph down three sides.
Just a thought!

 

[oldsaltoz]

A half lap onto the surrounding panel would not have gone amis. Easily cut with a router and no straps req'd. If you were feeling flash you could step it twice, but by the time you had done that you could have pulled out the scarph jig and routed in a scarph down three sides.
Just a thought!

I had to repair a skiff for a client that had been impaled by a bowsprit during a race. Cut out a square and scarphed it then cut a frame of ply to fit inside the hole with an overlap, ran the router round about 2 ply deep on the outer exposed section, then did the same on the patch as well as scarphing all edges to prevent the outer layer being pushed in.

Applied thinned epoxy (30% Methylated Spirits) till it would take no more than added some fibres to the mix and coated the join area taking care not to squeeze too much resin out. Cleaned up the excess resin and let it cure for 24 hours.

Sanded smooth, applied a couple of coats of thinned resin, then full strength over the top. After curing the surface was given a very light sanding with a 250 grit and wiped with acetone then two coats of high build epoxy primer.

Later that was sprayed with a 2 pack (International Interspray 900) and came up perfect. That must have been 12 + years ago and still looks great today.

Avagoodweekend......

Tip: To help get the resin into the end grain of ply, lay the ply on a flat surface on thin plastic sheeting, place a stick close th edge and drape the plastic over it, this will give you a small dam to hold the liquid resin close to the ply so it soaks is without having to do 10 trips wetting and re wetting the edges, just top up the dam, when it stops dropping use the resin on the race of the ply.

.

 

[fergie_mac66]

I always thought salt attracted moisture.

timber boat that get fresh water,rainwater or fresh condensates in rot very fast. The salt help to prevent any fungal attacks (dry rot) which can profligate in damp condition .If the timber is well protected from moisture absorption . The salt helps to stop any fungal growths attacking the timber.

Wet rot is a nuisance but If you get dry rot fungus then you can kiss good by to the boat.

Its worth putting timber fill its on the tops of ribs etc to stop drips collecting

and make sure your limber holes in the bilges are free and clear

http://diydata.com/problem/timberrot/timberrot.php

this site gives gives details of types of rot

 

[Tranona]

Don't forget this is a hard chine Ply boat and should be watertight. Provided you stop rain water from getting in through joints and fastenings (hence the importance of using epoxy on end grain in glued joints), just paint is more than edequate protection. I use Danboline internally up to the waterline and conventional paint above. Externally, if not sheathed a proper paint system is adequate, but some prefer to coat with epoxy first. Remedies and protection suitable for conventional timber construction are largely irrelevant.

 

[EastCoastChris]

Are you planning to coat the exposed ply and timbers?

Epoxy encapsulation is not necessarily the panaceae it may first appear to be. If I was building a new boat from scratch I certainly would epoxy encapsulate and put glass cloth on the outside. Retropsectively applying epoxy to just the outside of the boat does little to inhibit the internal freshwater that is the cause of most rot. Applying epoxy to the inside and effectively covering the entire internal surface without leaving any bare spots where water could penetrate behind would be next to impossible. One thing worse than water in the plywood is water in the plywood behind epoxy.

She's 30 years old and reached that age through the use of good quality plywood and being painted inside and out. I'm sticking to that successful approach.

A half lap onto the surrounding panel would not have gone amis.

It wasn't a joint in the plywood that failed, it was where freshwater had been held against the old chine log and hull in the middle of a panel.

timber boat that get fresh water,rainwater or fresh condensates in rot very fast.
Its worth putting timber fill its on the tops of ribs etc to stop drips collecting

I've not decided on the final solution yet, but I am planning on doing something to make sure that water doesn't collect somewhere other than in the bilge. I've thought about fillets but if you look in one of the pictures where the hole is cut above, you can see the member that the sink drain gate valve is sitting on. You can see the angle of the hull means that water would have to flow up and over some members.

As for salt, I'm a little puzzled by that one, I understand the idea to tackle the freshwater, but it does attract moisture and what stops it dissolving away into the bilges? I was thinking Intertox or some other sort of penetrating fungicide/preservative treatment before painting would be a good start.

Plywood boats can't be made rot-proof, but on the flipside they are almost infinitely repairable.

Chris

 

[Seanick]

Re: Half lap, I was refering to the repair!

 

[EastCoastChris]

Sorry Nick, I realised after I'd posted that I might have misread your post. Apologies

Chris

 

[fergie_mac66]

well salt is the old remedy. Intertox etc will do it but if wood epoxied then no penetration ( also serious poisons). I think the theory is the roots of dry rot (not called roots can't remember name) are microscopic they tunnel through anything into the into wood can spread right thought out the boat unseen. Little enclosed area small amount of fresh water moisture and dark,fungus can gro quickly.Salt stops fungus spores dead can't grow. the wood is protected from wet rot by epoxy and paint. well vented clean bilges common sense but there's aways that little spot . The moisture evaporates in warm weather but leaves the salt behind .Wet rot easy to cure cut and replace

mind you old remedy could be old wives tale but it makes sense as salt is a preservative

 

[EastCoastChris]

mind you old remedy could be old wives tale but it makes sense as salt is a preservative

No you're right, that's why rot is generally a consequence of freshwater getting in. I just couldn't quite understand how salt could be used in practice. Obviously it needs to be more sophisticated than throwing a packet of saxa into the bilge. I'd actually prefer it if the inside of the hull wasn't painted and then I could give it a good preservative spray once a year.

I think mycelia is the "roots" word you're looking for.

I'm trying to learn to relax as a wooden boat owner. OK the plywood will rot in time but it's quickly replaced and looking round there are plenty of GRP and steel boats with problems of their own. Most are considerably younger too.

Chris

 

[Tranona]

mind you old remedy could be old wives tale but it makes sense as salt is a preservative

This bit is right - salt is a preservative and salt water is preferable to fresh. However what you are proposing may be applicable to "traditional" wood boats which absorb water and leak. However, it is not applicable to Ply boats which are composite (wood and glue and maybe epoxy) where the intention is to eliminate leaks and keep the material stable. This can be done as already noted by ensuring there are no paths for fresh water to get into the ply and ensuring that any water (salt or fresh) does not lie in pools anywhere. If this is done, conventional paint finishes are perfectly adequate, inside and out, although my preference would be for epoxy coating as a primer. The rot on this case, common in this design would have been caused by a freshwater leak.

As I have noted several times here, my boat to almost the same design is 46 years old and has no rot in the main hull structure because it is sheathed on the outside, painted on the inside and no fresh water can get in. The less well protected upper works on the other hand has (or had) localised rot where fresh water has penetrated at bad joints or poorly sealed fittings. So far none has been extensive enough to resort to the scale of repair on Chris's boat - but as he says once you bite the bullet it is quite straightforward, but does require a bit of skill to get it right.

 

[Seanick]

Sorry Nick, I realised after I'd posted that I might have misread your post. Apologies

Chris

No worries, nice job though. Just paint her up as usual and its probably the only repair you will have to do for years.

Tranona-my boat is 'traditional' and does not leak-ever!

 

[Tranona]

I can believe it - did not say all traditional boats leak, just that ply boats shouldn't!

Thought of putting salt into a well built yacht gives me the shivers.

 

[EastCoastChris]

No worries, nice job though. Just paint her up as usual and its probably the only repair you will have to do for years.

I hope so! Although the work looks drastic by the end of this winter hopefully everything I knew of, that I have found or that the surveyor found will be completely sorted.

Thought of putting salt into a well built yacht gives me the shivers.

Bad for your heart too Maybe it should be lo-salt?

Chris