Parallax says:

snip

Also remembered that failure to properly countersink some screws on
the hull caused substantial delays in the finishing of #1 so I spent
several hours removing most screws countersinking more and replacing
to make sure they were really below the surface on #2.

ahhhhhh..... my favourite problem (as in the one I do most often) I don't
feel alone any more ;-)
I do find, however, that it is only really a problem in hardwoods, since I
usually underdrill the holes at the same time, making it inevitable that the
head shears off when I try to back it out to increase the 'sink.

Steve "now you know why I design 'em, not build 'em..."