My experience has been that floats do not prevent bee drownings.  I have
had better success using screen inserts or a piece of wood set diagonally
from the top to the bottom of the feeder.  Other beekeepers have suggested
loosely packed straw of hay in the feeder but I've found that the straw
or hay soaking in sugar syrup gets real rank real fast.  I think the best
results I have had has been with the diagonal wood piece.  I've been
meaning to try a V arrangement - two pieces of wood from both top ends
to the bottom center to see if that improves on the single piece of wood
but I havn't done that yet.  For the record, regardless of the methods
used, bees still drown in division board feeders.  In spite of that they
are still my feeder of preference and I keep one in each of my hives.  It's
always there when I need it and it's not a piece of equipment hanging around
in storage when not in use.  Sometimes the bees build brace comb inside the
feeder and this brace comb is far superior in preventing drownings than
any of the above methods.
 
Aaron Morris - thinking bees need Baywatch too!