Plywood planked dory

Quite right,, one must know ones own mind.

 

OK,, on to a positive note;
A reasonable plan of attack might be to use thickened epoxy to form a fillet, with a slightly concave surface, at the junction between plank and the edge of the lap(s),, after first making sure the plywood edges were well saturated/coated.
Then, to use glass tape of suitable width, (perhaps ~2in,) and weight to glass over the laps,, once that glass had their selvedge edges faired/smoothed, then the wider widths of glass, (the width varying according to plank width,) could be laid-on.
With some care quite satisfactory results would be obtained.

 

I would skip glassing above the bottom lap. Many succesful glued lap plywood boats have been built without fiberglass.

We have a 20 foot sloop with displacement around 3000 pounds. The planking is 9 mm or 12 mm plywood, riveted and glued with polysulfide (Boatlife). Floors but no frames other than a hoop frame to support the deck mounted mast. No glass except for the deck and cabin top.

 

With no due respect.

Glassing shiplap is a major pain.
Glassing shiplap is a major pain!
If you have not already read
Glassing shiplap is a major pain

Buy a sheet of plywood in your chosen thickness. Rip five feet of it into four inch wide slats. Fasten the slats on to the 3 x4 to mock-up shiplapping. Cover with fiberglass.

Repeat until you achieve acceptable results.

OR decide on a different method of construction.

Best of luck

 

As others have said, glassing is a major pain and completely unnecessary. You glass the chine inside and out with biax tape, and if you like the entire bottom on the outside, it's just for abrasion anyway. The rest gets three coats of epoxy and then varnish or paint. If you plan to keep the frames even 4mm ply is enough.
The best thing you can do is buy Oughtreds book on this subject. From amazons different vendors new and used, https://www.amazon.com/Clinker-Plywood-Boatbuilding-Manual-Oughtred/dp/0937822612 or from the publisher Clinker Plywood Boatbuilding Manual https://www.woodenboatstore.com/collections/boat-building-books/products/clinker-plywood-boatbuilding-manual

 

If you want to fiberglass over lapstrake, which is a daunting task, the edges of the planks need to be rounded and the inside edge or intersection filleted. With thick planking like you have, there will be basically no edge left to show a classic lapstrake. Fiberglassing the interior of the hull will be even more difficult. This boat will be in the water for only short periods of time, so fiberglassing is not necessary. All it needs is sealing with epoxy and a good coat of paint over it.

 

I appreciate all the constructive input. It would seem that there is enough resistance among everyone to glassing the boat that I will definitely be doing some testing before committing to that course of action. I will glass the bottom and the chine regardless due to the abrasion factor. The weight savings realized by not glassing would be of great benefit as well.

 

There really is no need to glass the hull if you don't use something like douglas fir ply.As an example,Merlin Rockets have been built from glued ply since the 1950's.







They are 14 feet long and 7 feet wide and will probably see more stress than a 13 foot semi-dory ever will and there is no glass over the ply.Glassing the outside of any hull isn't a fun job and while it does give a bit more toughness,the amount of work needed to get a good finish is considerable.I would only ever do it if I had to.

 

As suggested, I have purchased and read the Oughtred book on clinker plywood boatbuilding. I have also done more research into this whole ‘glassing of lapstrake hull’ issue and I must say I can’t find even one record of anyone on the whole sum of the internet who thinks it’s remotely a good idea. Even the folks who claim to have done it and had it turn out well said it ranked as a process they would never repeat and one of the worst experiences they’ve ever had. So thanks to all for steering me away from it.