Thread: Pelin Cherry refurbishment

Nice project. Good luck.

Howdy,

Where the plywood has checked - those little cracks along the grain - it can be hard to prevent it from happening again even with epoxy coating.

However a very light glass cloth can prevent it 100% even in checking prone plywood like Oregon (douglas fir).

The plywood is probably fine structurally even with the checking, but it is hard to prevent the paint from cracking over the top in he same places when it is applied.

By light glass I mean around the 2oz (70gsm) mark. It can be worth considering a bit more weight for the outside bottom of the hull but to do the whole hull with a more normal weight cloth adds a lot of extra weight and work. Particularly for a nice light boat like the Cherry.

Best wishes
Michael

Douglas fir (what you all call Oregon) can check under a light sheathing of glass. I've seen it check under 6 ounce fabric, but not 8 ounce. So, my recommendation is nothing less then 8 ounce, which is a moderate sheathing weight, still light, just not a "finishing" cloth.

Another trick I've used on Douglas fir checks is to use a flexible filler (okay now he's nuts, we thought it before, but this confirms it), Yep, a flexible filler.

Epoxy can be changed in many ways, one is to add solvents, which dilutes it and also weakens it. In fact, it doesn't take much to dramatically weaken epoxy resin. This is the key, knowing when to stop, regardless of what others might say. Add 10% by volume of denatured alcohol to the mix resin/hardener, then mix in your filler materials (silica, milled fibers, wood flour, etc.). If you putty knife this into the cracks, it will cure just like regular thickened epoxy, but it will have different physical properties. It's elongation will go from 5% (average laminating resin) to 20%, it's strength in compression will decrease by 30% (okay it'll go from,000 PSI to 10,500 PSI, so no big deal), it's tension strength will decrease dramatically (this is what you want), but it's stick to the wood will be just as good as unthickened epoxy. The perfect thing for cracks that have a nasty habit of changing in size.

Alcohol works because it has a moderate flash rate. A 50/50 mix of mineral spirits and denatured alcohol will give slightly better results, but it's more trouble then it's worth. Xylene is another good choice.

You can increase and decrease the amount of "flex" you get with the epoxy, but if you venture very close to the 20% by volume mark, you'll ruin the epoxy as a glue. I recommend you make a test batch with just thinned epoxy. Two flat bottom trays, one with a few ounces of straight epoxy, the other with thinned, let them cure a week. Pop both out of the tray and you'll instantly note the thinned epoxy is much more flexible. This is precisely how I figured it out and eventually tested different ratios and compared them to straight resin. You can fool around up to about 15%, but after this the physical properties seem to fall off a cliff, so you have to be careful you don't end up with tissue paper strength, but very flexible resin.


I agree with Michael that the plywood is probably sound. Just the top veneers have some environmental exposure and have checked. This looks like a fun project. Get it clean, really clean, then consider knocking it back to raw wood with something other then high speed tools.

Howdy,

It is unlikely to be fir ply in Australia. We only really see it (or saw it) as a construction ply. Also most boats of this era would have been built with a good quality marine ply.

So a light glass would work. Thanks for the additional info about how hard it is to stop checking in fir ply PAR - I will remember that when writing in future - good info.

There is a pretty limited argument for diluting epoxy in 99% of cases ... PAR is right for the other 1%. But I don't think you need to.

The Cherry is a very light boat so to preserve that is important. Light glass will be enough.

I agree that a light sheathing will be fine for anything other then Douglas fir.

Yes, you'd very rarely need to dilute epoxy, though on occasion, usually when trying to solve a difficult problem, you can alter the properties of goo with a solvent. I should also recommend you have a really good idea what type of epoxy you are fooling with and a fairly good grasp of the chemical dynamics.

Thank you for the suggestions. I have ordered some light glass and continue stripping the decks back. I have spent a few hours over the weekend reading previous posts about sheathing, epoxy sealing and painting preparation. There is a lot of great advice, I previously always applied epoxy then glass then filled the weave, now I can see why I ended up using way too much epoxy and I look forward to trying some of these "new to me" techniques.

As far as 334 goes further cleaning inside and out, removed the grey non-slip material that was glued on with contact adhesive in the cockpit and scraped, rubbed and sanded off the contact adhesive and other bedding compound. Removed the rotten timber supporting the mainsheet traveler.

Welcome to the world of the Cherry 16.

It is a great light weight boat and was the first Trailable Yacht design built by the stich and tape construction technique.

She was designed for New Zealand conditions so the Australians added a larger set of sails including a fully battened mainsail. Some of the boats were built in all cedar ply and fully rigged came in at 220kg. A few of the boats were also built in the UK, USA, South Africa and PNG.

The number 344 is the Plan number, some 100 plans being sold in Australia by Trailaway Yachts. Thus, the boat would have been built in the late 1980s. The Australian Maritime Authorities gave the sail insignia CH, and the details of the larger racing rig are shown on the Yachting Victoria website under Trailable Yachts CBH detail specifications. This design is about 5% quicker than the NZ rig shown on the original Pelin Plan. At one stage there was an Australian class association which held championships but this folded some eight years ago

I have just checked with a friend who built two Cherry 16s. He says many of the boats were built using the West System including all their glue and filler powders plus using their solvents and accelerators. The cedar ply was very soft, so when it cracked they tended to just use a West diluted 400 series glue mixture and sandback.