Ron, Thanks for catching that. R/Jay Resepectfully, Jay K. Jeffries Andros Is., Bahamas Save the whales, collect the whole set. From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of ronleonard@shaw.ca I would add that though there is little differential pressure across the hull of an ambient sub, the hull still requires great strength from the roof to the base. The sub's ballast is likely carried on the bottom of the sub, and the air inside the sub is lifting against the roof of the sub, in opposition to the ballast. The hull needs to be strong enough to withstand this stress. Ron |