Hi everyone,
Phil is, of course, correct about the external stiffeners. It takes more load to buckle a frame in tension than it does in compression. No short cuts in the welding though! It has to be full penetration all the way for external frames.
Greg
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Phil Nuytten
Sent: Monday, June 18, 2012 12:07 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] My current submarine design: Specs and picture
Hi, Chris!
You might want to think about putting the 'T' stiffeners on the outside of the hull - much easier to do and gives you a lot more room inside, or, if you're happy with the volume inside the internal stiffeners it will allow you to decrease your hull diameter by twice the height of the stiffeners.
Seems counter-intuitive, I know, seeing that the hull is in compression - one would think you'd want internal stiffeners to keep the hull from 'collapsing'. The external T's will do almost exactly the same job - as the hull membrane between the stiffeners tries to 'collapse' it has to to pull the verticals into an asymmetric buckling mode (like a wavy ribbon) - the horizontal 'T' top flat bar won't allow the vertical to begin it's wavy buckle.
The internal/external stiffener difference in depth rating is quite small, but the ease of fabrication and other advantages are significant.
Good Luck with your sub!
Phil
----- Original Message -----
From: Christopher Graca
Sent: Sunday, June 17, 2012 7:14 PM
Subject: Re: [PSUBS-MAILIST] My current submarine design: Specs and picture
Emile, thanks for the pointers. I was originally looking at 10-20kW with the thought that I would normally be running the main prop at part load while cruising, and having additional overhead if needed. Maybe I'll look for between 5-10kW instead.
Jon, I've attached a new picture showing dimensions. I mis-typed 10' 4" when it is actually 1' 4". With regards to adding weld build-up to dissimilar thickness parts, does it need to be a 1:4 gradient? Also, the ABS spreadsheet shows 1136.2psi allowable working pressure for 5/8" 40" OD hemi-sphere (39.375" mid-plane diameter) with a .67 usage factor. Is there something that i missed doing in the calc?
-Chris
On Sun, Jun 17, 2012 at 4:57 PM, Jon Wallace <jonw@psubs.org> wrote:
Hi Chris,
Recommend more specifics when describing your sub, for example giving distinction between length of pressure cylinder and heads. Keep them separate. You said 10 feet 4 inches for overall length of pressure hull and I assume that includes the hemispherical heads. Deducting 40 inches for the heads it looks like the pressure cylinder is 84 inches in length. At .625 inch thickness with .5 inch thick ribs at 24 inches on center the ABS hull calculator on our web site is showing me a max depth of 1526 feet. It is also showing me you'll need .875 inch hemi-heads which would provide 1575 feet. So one inch hemispherical heads are not out of the question especially if 7/8 inch is hard to find, but you'll be looking at some welding build-up to match the heads to the pressure vessel.
Jon
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