Re: [PSUBS-MAILIST] Stopping Flaps

In a message dated 8/27/2008 6:43:40 P.M. Central Daylight Time, bottomgun@mindspring.com writes:

Dean,

Can’t we work a little nuclear power or warp drive in here some how to make it really interesting? J Now that would be going fast!

Jay

Respectfully,

Jay K. Jeffries

Andros Is., Bahamas

Talk sense to a fool and he calls you foolish.

    - Euripides (484 BC - 406 BC)

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Recon1st@aol.com
Sent: Wednesday, August 27, 2008 7:26 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Stopping Flaps

Wooahhhh all. I think something got lost in the translation here.

No rockets are intended here. Just a little sea anchor like a parachute.

the only high pressure air release would be to blow the folded up sea anchor out of its

compartment.

And the high speed I refer to is about 6 knots and I will be 20 to 30 feet of the bottom.

Just would feel better being able to stop when I need to. And this little parachute seemed

like a good idea.

Dean

In a message dated 8/27/2008 1:07:11 P.M. Central Daylight Time, ag@desertstar.com writes:

I agree 100% with Jay's message and hence the "The following should be filed under "insane" caveat.
Perhaps that should be changed to "ABSOLUTELY INSANE". I was just trying to think of alternatives to those already discussed and crossed off the list.

I can also not really imagine a scenario where high speed at the bottom would be useful. A relatively high speed (i.e powered) descent from the surface to near the bottom can be nice if it can be accomplished safely and you are going deep
In response to Jay (and no I am not really advocating the use of high pressure retro-rockets...but in the interest of curiosity (which did kill some cats):

Propulsion CAPABLE of high speed can be useful to fight currents.

1) You really care about momentum, so you can trade off your reaction mass with the velocity you expel it. Of course at this point you may have to up-scale from scuba bottles, which is probably WAY more dangerous than the risk of hitting something.

2) Didnt see that mythbusters. If you have a gas compressed in tanks to a higher density than water, you shouldn't loose any buoyancy (DONT TRY THIS), and was thinking more about fast horizontal delta-v near the bottom, where a loss of buoyancy is not the major concern.

3) if it was for absolute emergencies then a stuck valve doesnt seem like a terrible price to pay. Assuming there was a redundant system to blow ballast.

Also, some shallow water wet subs can move pretty fast. But they dont have the mass behind them that would make a collision as dangerous.   Also some of those bigger psubs may cause a pretty big mess at low velocity collisions.

So maybe "PSUB momentum kills" ?

or really "Operate in the envelope" is probably the correct message.

FWIW: Deep Flight I has a max cruising speed of 12 Knots and a Min of 2 Knots. But I think the idea is that it is super maneuverable rather than able to break, and high speed is used primarily for descent.   Still cant imagine12 Knots at the bottom...heck 2 knots seems fast. It does only weigh 3000 lbs...

-a

-----Original message-----
From: "Jay K. Jeffries" bottomgun@mindspring.com
Date: Wed, 27 Aug 2008 16:35:32 -0700
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Stopping Flaps

> While Andy's idea appears feasible on the surface, there are some practical
> issues to consider:
>
> 1.    Air does not have a lot of mass so its reactive force would be small
> in comparison to the 2+ tons of a typical PSUB;
>
> 2.    As demonstrated on Myth Busters, dumping a lot of air into the water
> in the direction of your downward trajectory will actually cause you to have
> a loss of buoyancy and thus accelerate your descent;
>
> 3.    Dumping that much air (it is going to take a LOT!) at one time will
> probably freeze up the valve you are using (unless it is the VERY expensive
> Marrotta valves used for big sub's ballast tank blow systems).
>
>
>
> Under most conditions found in typical PSUB operating areas, trying to
> propel your PSUB at high speeds can be likened to driving in a heavy rain.
> You can drive fast, out driving your visibility window, and risk colliding
> with a car or something else before you slow down to avoid the collision.
> Or you can slow down and drive within your visibility window and be able to
> easily avoid obstacles. Your PSUB weighs several tons and you do not have
> breaks like a car, trying to stop a PSUB's inertia is like trying to break
> your car with your foot out the door on the road. SONAR will help see
> things ahead but your reaction speed and the maneuverability of your PSUB
> (stopping or turning that inertia) will not help you. An issue here is a
> thermocline can cause the SONAR beam to bend around an obstacle and you may
> not see it until too late. Any high speed vehicle in the water stays up off
> the bottom to avoid obstacles and this defeats what the PSUB is trying to
> do, find things on the bottom. You need to slow down if you are going to be
> near the bottom.
>
>
>
> It took years for many of the things learned in the Technical Diving to
> permeate out through the old, hard core deep wreck diving community in the
> NE United States. One of those things was "Deep air kills!" Well, thought
> should be given to "PSUB speed kills!" Other knowledgeable people have
> tried to impart this fact to the list. Dean has put a lot of effort into
> his PSUB to conquer this very trying environment found in the Great Lakes
> and should be applauded for his efforts but care should be taken in how PSUB
> speed is promoted.
>
>
>
> There are others that seem to periodically bring the same topics up just to
> stir the pot. A healthy discussion of these subjects is good but the
> concepts should be couched with notes of caution, not as realities and
> proven technologies. In fact, usually when there is a citation that appears
> that the subject is safe or feasible, further investigation leads to hoary
> facts.
>
>
>
> Your resident naysayer,
>
> Jay
>
>
>
> Respectfully,
>
> Jay K. Jeffries
>
> Andros Is., Bahamas
>
>
>
> Talk sense to a fool and he calls you foolish.
>
>    - Euripides (484 BC - 406 BC)
>
>
>

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