: I'm contemplating building a Pygmy Triple, and have read enough tandem rescue
: horror stories to be concerned about the amount of water it could take on.
: Sea socks are one option, but it seems that the space outboard of the
: cockpits could be used for fixed flotation. I've used carved 2"
: sheathing foam to fill uneeded space in plastic boats, but was wondering
: if anyone had tried pour-in-place foam, longitudinal bulkheads, or other
: methods.

second your and shawns bulkhead approach

because tandems and triples usually are quite wide, there'll be even more space and reason to put in the longitudinal bulkheads to reduce cockpit volume as much as possible.

if weight is a factor, consider strapping in longitudinal inflatable drybags. or bag backup in the longit bulkheads. tossup here, bkhds more volume but more wt.

it seems natural to use the excess volume as simply as possible (ie bulkheads or strapped(netted??)bags) to reduce the problem.