Re: [PSUBS-MAILIST] Hull material

Rick,

I am truly impressed with your continuing ability to pull out obscure and nearly impossible to find reference material seemingly without effort. Very impressive!

Joe P

From: "Rick and Marcia" <empiricus@telus.net>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
CC: "\"Rick & Marcia\"" <empiricus@telus.net>
Subject: Re: [PSUBS-MAILIST] Hull material
Date: Thu, 29 Dec 2005 01:50:35 -0800

Hi, Robert - I don't think we've "met". Welcome :-)

I get the impression, and please correct me if I'm off the mark, that you'd like to maintain the freedom of designing a sub with compound curvature, possibly avoiding the "tin can" look (no offense to the tin can guys!!!).

One option, and this is in support of the steel crowd, is to build your pressure hull using the basic engineered-to-death shapes another member suggested. Cylinders, end caps, plate, etc. Use the composite to form an ambient pressure fairwater around your "tin can" in any shape you want that's hopefully hydrodynamic. You maintain the safety factor of proven engineering AND pull off the artsy side.

Second option would be to, as Carsten suggests, use ferrocement. It too is proven. Concrete is easy to work with and very tough. With a tiny cockpit as you mentioned I'm not sure your hull thickness would compensate for the buoyancy inherent due to the cockpit's volume. You may be a little on the heavy side for a hull going to 300 feet. You do not want this unless you are prepared to design in permanently sealed hard tanks as extra buoyancy or to use syntactic foam (expensive). A way around it would be to simply design a more voluminous cabin (to a point).

Personally I love concrete but I'd test a full sized hull to crush depth. Too many unknowns. Try to find the paper written by David A. Smith called "Feasibility Study for Concrete Submarine". The research was carried out at UC Berkeley (contract number N66001-74-C-0408, Naval Undersea Center).

The nice thing about concrete is the potential for compound-curved pressure hulls. One hull period.

Third option would be to design a composite ambient pressure hull but that doesn't address your wish for a deeper diving sub. Strictly scuba and you need to have your C-card for that whether you're wet or dry. I wouldn't even begin to consider depths beyond no-decompression scuba limits because of the gases involved in the breathing mixes. An emergency ascent will kill or maim you.

Fourth option is to build the bottom or base of your sub in steel (no flat plates here) and use a plexiglass bubble for the top half of your pressure hull, vis-a-vis, . You can't beat the visibility and even a large half dome isn't, um, too expensive (see below).

Consider, as well, reducing your depth needs to, say, less than 150 feet. That gives you a LOT more room to mess around with plexi domes, costs, etc.

Warm regards,

Rick Lucertini

Vancouver

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