Inside plank treatment

Question. After striping old paint and varnish from the inside of the planks and frames, what's best to treat or coat the inside surface?..Short history first..
I'm restoring a 5.5 M sloop. She's VERY dry. Some seams are over 1/8 in (originally no caulking). I've read that a ethon-gycol-water spraying will help swell her back up . Mahogany plank over oak frames.

 

It will also not let any paint adhere to it. Are the planks varnished in the inside? Do not add a lot of caulking between the planks or the frames and fasteners will break. You will be better off hiring someone to inspect the boat.

 

So you're stripped to bare wood?

I have found that the best way to swell ax and hammer handles is to soak as you've described.

However what I think Gonzo means is that wood so treated will not take a finish.

I will assume 2 things:
1) the boat is and has been out of the water for some time.
2) when it goes back in the water, it will stay there for the season.

Some builders recommend that when haulng a boat for the winter that it be placed in a barn with a dirt floor; the dampness of the dirt will reduce shrinkage over the winter.
After the inspection Gonzo suggested, I would cover the inside of the hull with old linens or blankets and give it repeated daily spritzing with water. After several days the planking should make up, at least as far as it can. I would be very cautious about the application of caulking compound if you still have any gaps afterward. You may want to then put her back in the water and wait a day or two for the planks to expand further. This may require some pumping as you go along.
If she seems to make up tightly, I'd haul again, give her a few days out of the water to surface dry, then soak the inside of the hull with linseed oil cut 10% with turpentine. Warmed up on a double boiler helps. You might then have to assess the exterior of the hull and decide what to do with that... perhaps a scraping, sanding, Dolfinite where needed and a good painting?

Hopefully others will chime in.