Decided to oipen up the other side of the bow to inspect the mast
step/dagger board box. I am glad I did because I found the Gorilla
Glue I used when I began these boats has not held where it is immersed
in water. Somehow water is entering through the dagger board box and
has weakened the glue joining the box to the bottom. I cleaned out as
much of the old glue as I can and I plan to inject very thin epoxy into
the crack and then use a fillet of epoxy over the joint followed by
glass over that.
When I put the access ports on the bows of boat #2 I found no evidence
of water entering and I think this is because I started to use epoxy
much more extensively when I assembled it although it also has some
gorilla glue.
As far as bathroom underlayment goes, I would never use it again for
anything except firewood. After building the MiniCups, I built a
nesting dinghy from 1/4" marine ply and it has had a lot of use and it
shows no signs of material failure like the MiniCups.