Re: [PSUBS-MAILIST] Re: high speed subs

["Captain Nemo" <vulcania@interpac.net>]

----- Original Message -----
From: <VBra676539@aol.com>
To: <personal_submersibles@psubs.org>
Sent: Saturday, February 26, 2000 2:23 AM
Subject: Re: [PSUBS-MAILIST] Re: high speed subs


> Pat,
"Speaking of control, how does your trim system handle the dread
"settle-butt" syndrome under power. . All the old Perry boats had big wheels
aft but invariably changed fore and aft attitude underway in mid water. Even
my little guy does it."

Damn!  I should be getting some sleep before I've got to go into work
tonight; but you've got me thinking about this.

Lemme ask you a question first.  (Captain Kitteredge sent me a picture of
him in his sub a few years back).  I'm not trying to be funny or offensive
here; this is just the easiest way I can ask the question: Does your sub
look like a propane tank with a turret, and an inverted canoe on top?  In
other words, is the pressure hull a cylinder with torroidal end caps;
there's a turret in the top center; and you've got some kind of
superstructure (your ballast tanks?) on top that is naviform in shape,
pointed in the bow and stern?  (That's what the sub Kitteredge was in looked
like.)  Well if it does, I think your "settle-butt" problem could be a
consequence of drag and poor relative hydrodynamic flow.

Visualize the boat I've described above underway underwater.  In front, your
catching impact drag on the front of the torroidal endcap.  It can flow back
along the sides of the hull; but above it gets pushed up, creating impact
lift under the bow of the superstructure.

Aft, the flow along the sides of the cylinder drops abruptly off over the
end cap; gotta create an eddy of disrupted flow, and that creates an area of
reduced pressure aft of the end cap which would pull down on the stern
superstructure above it.

Combine that impact lift in the bow, with the reduced pressure drop in the
stern, and you've got your "dread settle butt" syndrome.

How to beat it?  Build structures to enhance flow and defeat the effect fore
and aft.  Install horizontal stabilizor fins running the length of the
pressure hull and/or along the superstructure.  Incorporate control surfaces
and or thrust vectoring to counter the adverse pitching tendency.

Probably other ways, too.

I know you've been looking at your sub for 15 years and I've been thinking
about it for 15 minutes: you must have thought of what I'm describing,
right?  Anyway, it seems like a possible cause of the problem you're
describing.  Just thought I'd run it past you.

Gotta go,

Regan