Frank, If you do draw a vacuum while towing on the surface and your tanks are stiff enough, it will not be an issue until you slow down. Water would then be drawn back into your ballast tanks and your sub will settle in the water. Might be a good thing to put on your sea trials list that you have someone in the sub when you do your first high speed tow so that when you slow down and if water is drawn back into the tanks, that you have someone that can blow ballast if she settles too much in the water. Long chance but better to be prepared. R/Jay From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of ShellyDalg@aol.com Ya Jay. I wondered about a small amount of vacuum actually "pulling" water into the tanks. The 12 gage stainless tanks will withstand a little vacuum or over pressure. They are actually pretty rigid. The reason for having the tanks so "closed" with just the small openings on the bottom was to insure I could keep air in them even if the dive angle got severe or possibly really rough water at the surface. I'm pretty sure whatever vacuum that could build up would be far lower than what it takes to buckle the tanks. The series of lengthwise "breaks" or bends on the surface adds a lot of rigidity to them. The breaks also add visual appeal as it resembles the wood strips on a skiff. A couple of "soft " spots have stiffeners welded inside so the tanks should be able to take a pounding from surface towing, waves, and impacts against rocks when submerged. I had originally planned on making FRP tanks to avoid rust but opted for metal ones because of impact. Much better to dent a tank than crack it. Plus I can polish the stainless like CHROME ! ( damn Harley riders ! ) Frank D. |