Our boat (wooden '58 Chris Craft) leaks a bit. I believe it's where the
final "plank" meets the keel. It's not so bad that I'm scard of any serious
problem but it is bad enough that a puddle of 10 gallons or so forms in the
back when we're running. (It forms in the back because the bow is up, and
the bilge pumps are in the front.)

I'm thinking I'll use some tool (?) and forms a small groove (kind'a "V"
shape) between that last "plank" and the keel and then fill it with ...
4200?

Actualy it isn't "planked" it's lap-strake plywood.

Make sense?
4200 the thing?
Maybe M101.