glued plywood lapstrake

[Stashu]

Any suggestions for defining or establishing the width of the overlap in the glued plywood joint? I'm working from the designer's offsets with the caveat that they are approximate, and that fairing will be required in the fitting process. The garboards are in place. However, the adjoining plank, lofted from the designer's offsets, will fit only with significant reshaping of the garboard, including also a variable overlap ranging from 1/2" to 1/1/8". Is this acceptrable in a 13 ft. hull? I'm beginning to think I should just ignore the available offsets and spile?

[Don Bailey]

When I built my Pooduck Skiff, 12 ft 10 inches, the glued lap was 1 1/8th to 1 1/4 inches. Plane and test fit many times till you are satisfied the strakes will fit. Don Bailey

[Don Maurer]

That's one of the problems working with offsets. They can't take into account small variations in the mold setup. Get a copy of "Ultralight Boatbuilding" by Tom Hill. Use the offsets to lay out the stringers, then adjust them by eye until they look right. Trace your plank shapes off the stringers. Ideally for 1/4" ply, the overlap should be around 3/4".

[rmiller3]

I agree with most of the points made above.

One further consideration in glued lap construction is the number of planks from garboard to sheer.

Given that a properly done epoxy joint is stronger than the planking material (most likely ply for the planks), the number of planks per side , which is also to say the width of each plank, must be considered in the required overlap to achieve needed strength of the glued lap.

Obviously, the plans and designer's recommendations should be followed with respect to the size of the lap. In general though, narrower plank width may permit smaller laps than will fewer planks per side with greater plank width, to achieve the same overall strength.

Robert

[Clinton B Chase]

John Brooks says..."We use a 3/4" lap on our small boats up to 18'. If your planking is more than 1/4" thick, consider increasing the lap width, using three times the thickness of the plank as a rule of thumb". Seems that lap width is a function of plywood thickness.

Cheers,
Clint

[Graham Knight]

I'm building Iain Oughtred's Acorn 13, and the lap is specified as 5/8" (16mm). Because the planks sometimes need a little reshaping to get a perfectly fair curve, the actual width sometimes varies by 1/16" or so either way, but seems perfectly adequate.
I would say definitely spile the remaining planks, it's quicker and they fit properly, make patterns from cheap ply if you're scared of wasting expensive marine ply.

[David W Pratt]

Just built CLC's Eastport Pram. They call for 3/8" router rebate 1/2 teh thickness of the ply. Seems to work.
Good luck.

[Garth Jones]

I recently finished planking my Ness Yawl. The hull is 3/8 ply and Iain Oughtred specifies 3/4 laps. In my boat it definitely varied here and there. I spiled all the planks because there was enough variance in the whole thing.

Cheers,
Garth