[PSUBS-MAILIST] Ribs outside hull

[Sean T. Stevenson via Personal_Submersibles]

The ABS Rules provide a separate set of equations to use for determining all of your critical pressures when using external framing. You need to calculate accordingly. In general, external framing provides more stiffness than internal for the same amount of material, but there are drawbacks.

Welds between your hull shell and any external stiffeners must be CJP, as opposed to simply continuous.

Also, be aware that free filling spaces between the pressure hull and any external hydrodynamic fairings represent a large volume of water which must be moved along with the hull, and that inertia will consume a substantial fraction of propulsion power. If you have no fairings, you will still be moving a boundary layer defined by the drag of the exposed stiffeners, so you must plan your power budget accordingly.

You also need to figure out how to mount all of your internal equipment, since external framing implies the loss of what would otherwise be a bunch of convenient structure for clamping to.

Sean

-------- Original Message --------
On Sep. 1, 2023, 11:44, Raphael SOULIAC via Personal_Submersibles wrote:

> Hey guys, i've got a quick question. The design i'm working on has a very narrow hull (ØID 650mm) so i wanted to put the renforcing ribs on the outside of the hull.
>
> The ABS spreasheet give me 1113ft of max depth but it's for the ribs on the inside.
>
> What would be the difference between this and the real max depth ?
>
> Raphael
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