Spiling Anxiety

My garboard planks were off by about 1/4" or so. I trimmed one down at the bow to help close a gap and the other I filled the gap with slivers of ply and trimmed the outside edge a bit. Not too difficult a fix with the mating edges of the two planks and the keel plank butting up against one another.

The next planks are overlapping (hence, lapstrake). Any failure to overlap the planks will be a real problem, probably mean I'd have to buy some more ply, scarf etc. etc. I really want and need to get this right. 

Truth is, if I'm only 1/4" off, I'll have enough room to play with since the laps are designed to be 3/4". That would make a smaller lap, but I think the boat would stand up to that. 

What to do? 

There are at least 3 options: go with Clint's measurements, spile using a plywood batten, or spile using a "lattice" method (my terminology). I used the plywood method for the garboards. Whichever method I go with, I could always make a dummy plank with cheap plywood (is there such a thing anymore?) and see if it fits before going with the $100 a sheet ply. 

I've gone to the trouble of prepping for the 2 DIY methods.

Here is the plywood batten pattern.

I doubled the ply to give it more bulk and made sure the ply laid down without twisting or binding before gluing in the middle. You can see screws in the sternmost piece and wedges in the piece toward the bow. This batten needs to sit flat without and forcing. I laid the pieces down from the outside to the  middle and glued the two pieces together with hot glue rather than screwing them together as I did for the garboards.

Then I made a pattern with  battens and cross pieces.

Here they are overlapping each other.

I may transfer both of them to my plywood and see how they compare. I may be able to use my compass and compare while they lay on top of each other.

Are they really close? Or is there a substantial difference? 

I might be able to slip down there later tonight and check but it may be next week before I can tell.