[PSUBS-MAILIST] Submerged speed calc

Hi Frank

"I hope to be able to get 6 knots submerged speed out of her."

As I understand it, your typical fast attack submarine is faster submerged then when surfaced. This because on the surface, a displacement hull speed is calculated at 1.3 x the sq rt of the waterline length. So submerged, the surface wave no longer factors.

So my question then...is there a rule of thumb formula that can be applied to a submerged body? Or does one have to calculate total plate area -vs- resistance of seawater and then account for thrust?

Joe

From: ShellyDalg@aol.com
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] CAD help!!!
Date: Sat, 27 Jan 2007 20:47:08 EST

Hello Pierre. That would be nice if we all offered our talents. I would appreciate any work you could do on identifying weak spots in my design.

In turn, maybe there is something I can do for you.

How would I get a drawing to you?

My sub is of a slightly different design than the Kittredge.

More of a clam shell than a tube, with semi-hemispherical tank ends as top and bottom, rather than ends on a tube. Kinda like a squashed sphere.

My model testing shows that it should offer more free-board, shallower draft, and more usable space inside than the tube design.

The hydrodynamics are a little less efficient than a long slender tube, but at slow speed ( like most psubs ) the difference is negligible, and I'll have room for comfortable, side-by side seating.( if I can find anyone brave enough to try it! )

I've finally got the parts into fabrication ( 5 months of haggling ) and hope to see them in a month.

Windows have to be the weak spot, and I'll be putting 4 inch "T" ribs inside in the areas that need additional support.

Expected depth is about 300 feet with 2 inch thick windows, but my guess is that most dives will be 100 feet or less.

Approximate weight is 8400 lbs. for the 84 inch diameter/56 inch tall main hull.

I hope to be able to get 6 knots submerged speed out of her.

I look forward to hearing from you......Frank D. (408) 353-6645 Calif time.