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

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

Yo, Vance!

Well, I sent you a long one about this problem yesterday, dealing with the
possible effects of "torque and p-factor" upon the structure.  I'm still
thinking it through.

(First of all, I accept that this is a real problem.  I get the impression
you are an old sub driver; Joe says he's found reference to "settle butt
syndrome" in books; and if it's been known to happen to fleet-subs, it's got
to be real.)

What you just said about a similar problem in Blimps has me thinking;
especially that part about the similarity between blimps and subs with
reference to the CB and CG, and the thrust line of both vehicles being well
BELOW it's central axis and CB.

Torque and p-factor might be part of the problem; also, pulling
prop-overhanging structures into an area of decreased pressure makes some
sense.  But I'm beginning to see something even simpler, as well.

Maybe this is also a consequence of FORCE versus INERTIA.  (How to make this
simple?)  The prop starts spinning, but it takes a moment to overcome
inertia.  The weight of the boat resists the thrust of the prop.  If it
can't move forward,  maybe the prop is sort of "chewing it's way down" into
the water like a buzzsaw blade into wood, pulling the stern down with it.

I know that description is laughably untechnical, but pick up a model sub;
put your palm in front of the bow to simulate inertia; and visualize the
result of a thrust vector  situated THAT LOW BENEATH THE LONGITUDINAL
CENTERLINE AND C/B.  I think I can see it how it might pull the stern of the
boat down.

The feeling I get is that this might be a consequence of all the possible
forces we've been discussing, working together to destabilize the boat in
pitch prior to getting underway.

What's got me bugged now is why my NAUTILUS MINISUB doesn't seem do it?
Maybe because my prop is small; my power to weight ratio is low; there isn't
any broad hull surface over the single prop; and my thrust line is not
below, but on, the longitudinal centerline of the boat?  Maybe it wants to d
o it, but the forces generated are minimal in comparison to the weight of
the boat?  (There's a LOT of steel on the bow, counterbalancing the tail.)

HMMMMM.....

Pat