The main thing to understand in the relationship between web and flange dimensions is that the effectiveness of the stiffener improves with it's moment of inertia around the point of contact with the hull. Consider an over-simplified example of a stiffener made of nothing but a bent rectangular bar. You could build it two ways; bending the rectangular the "easy way" so it's long side is in contact with the cylinder, or the "hard way" so it's short ends are the ones in contact. In both cases the mass of your stiffener would be the same, but clearly the deeper ring formed the "hard way" is going to be very much stronger. This is why we use T stiffeners, to put as much mass as possible away from the hull, thus increasing the moment of inertia. Of course everything has limits, so you can't make a web that's paper thin and expect it to support a massive flange. Take an iterative approach varying the geometry until you find the various failure modes occur at roughly similar pressures. If you choose to use undersized stiffeners you will just have to stay within the limits of the weakest failure mode - the strength of a chain being determined by it's weakest link. So long as you have calculated the strength of that link and stay within it, you should be OK -- with a caveat. Please bear in mind the calculations are extraordinarily sensitive to out-of-roundness. When you fabricate your hull, you will find the stiffeners force the hull into a proper circle. I would advise the stiffeners at a minimum be strong enough to deform the hull when inserted, and not the other way around, or you could get an out-of-roundness problem. Cylinders alone, at least in my experience, don't come from the supplier in anything like acceptable roundness. One of your questions I don't have an answer for, and that's why the depth rating actually decreases when you overdo the stiffeners. I've wondered about that one many times, and if anyone has an answer I'd love to hear it! Thanks, Alec The contents of this e-mail are intended for the named addressee only. It contains information that may be confidential. Unless you are the named addressee or an authorized designee, you may not copy or use it, or disclose it to anyone else. If you received it in error please notify us immediately and then destroy it. From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of abyssalobsession@gmail.com Sent: Wednesday, December 09, 2009 11:20 PM To: Psubs Mail List Subject: [PSUBS-MAILIST] Abs calculator I have been in the process of putting my rough sketches into actual hard blueprints. The only thing that really confuses me is the design of the stiffeners. I understand what the different dimensions represent, but I don't know what their relationship to each other is. How does web thickness, web width, flange width, and flange thickness affect each other. Why does having stiffeners too beefy make their max pressure go down? And last but most important if I choose to use smaller stiffeners than what is most efficient for the hull thickness, are their any significant risks as long as I am operating within the maximums. I know these would probably require a degree in engineering, but I am still a few semesters away from this kind of stuff though. I appreciate any insights. Sent from my Verizon Wireless BlackBerry ************************************************************************ ************************************************************************ ************************************************************************ The personal submersibles mailing list complies with the US Federal CAN-SPAM Act of 2003. Your email address appears in our database because either you, or someone you know, requested you receive messages from our organization. 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