We use Dove, Dial, Ivory, or Irish Spring*depending on what's in Costco on the day my wife shops for bar soap. All of these wash off pretty quickly. However, I wonder if it has more to do with the water you're using than the soap. I've noticed when traveling for work that some places take forever to rinse off the soap while others are like home--- and I'm using the same bar of soap in all these places.
I think the "harder" the water, the more it takes to rinse off soap, but I could have this backwards. Maybe it's real soft water that's the problem.
As to how much water we use to shower on the boat, we have a handheld shower head with an on-off button, so we get ourselves wet, then shut off the water with the button, soap down, shampoo, and then hit the button again to rinse off. I would guess, judging by the amount of water in the shower pan before we pump it out that one shower typically uses between 1 and 2 gallons, but that's just an estimate based on what I see underneath the grate.
I like your new avatar photo, Eric. It shows off your boat better.
-- Edited by Marin at 23:00, 2008-02-01