Ahhhh, the smell of the sea!!!

Unfortunately, our sailboat smells (stinks, actually) despite cleaning
throughout, checking the head & plumbing/holding tank, scrubbing the
bilge, and everything we can think of. We haven't found any definitive
source of odor, and it may just be a combination of all of the sources.
We have pulled up floorboards to check for mold and removed panels and
mounted items to clean behind them.

There must be something we are overlooking - has anyone else had
success overcoming general smelliness? Also, has anyone tried this
http://www.defender.com/product.jsp?path=-1|7504|72870&id=443202 - I
came across it in my search for help.

-Nancy