RE: [PSUBS-MAILIST] Hydraulic Drive Unit

["Alec Smyth" <Asmyth@changepoint.com>]

Walter,

This sounds as if you were dissuading Gary from some hair-brained design concept, and I think a rather important fact might have fallen through the cracks. That is the fact that Gary's sub Vindicator is no design concept. Its a superbly constructed, even beautiful boat, and it works very well indeed. 

In any case this is a moot point. In an earlier post Gary pointed out that in hindsight, he recommends compensated trolling motors for their simplicity. 

rgds,

Alec 



-----Original Message-----
From: Walter Starck [mailto:wstarck@ozemail.com.au]
Sent: Wednesday, November 20, 2002 12:23 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Hydraulic Drive Unit


The points you mention have all been successfully addressed in numerous
designs without incurring the additional cost, bulk, complexity and
inefficiency of hydraulic propulsion.

On your specific points.

1. Directional control is adequately provided in almost all larger subs
by rudders, nozzles and diving planes. In small subs requiring high
stationary maneuverability external steerable motors are preferable and
have proven to be very reliable.

2.  Carbon/ceramic shaft seals are readily available, highly reliable
and not expensive.

3. Reversible motor switching is again common, reliable and not costly.
It presents no problems that  make hydraulics preferable.

4. Weight distribution of electric motors is likewise a non-problem in
this application.

5.  Certainly hydraulics would be an excellent way of  moving ballast
weights but this can be done quite effectively by a simple manually
powered system.  In any case having separate systems is generally
preferable to having everything dependent on a single central system.

6.  Pressure resistant motor housings present no major problems and are
reliable.  On the other hand pressure equalization is also not difficult
to reliably achieve.

7. Anything that leaks presents a problem but the means to avoid this
are well known and not difficult to do.  Leak detectors and inspection
ports are also easy to provide.

8. Although hydraulic motors are compact the entire system is not and an
even larger motor is required to compensate for the power loss from
hydraulic and mechanical friction such a system imposes.

The reason existing subs don't use hydraulic propulsion is not because
everyone else is stupid or unaware.  Many subs do in fact often use
hydraulics for other functions.  They don't use them for propulsion
because they don't offer any important advantage and do have
disadvantages for this purpose.

You can, if you choose, do it and if  properly done it will work well
but it solves a non-problem at the cost of  added expense & complexity
plus reduced performance.

Walter Starck
Golden Dolphin Video CD Magazine
The premiere publication of diving and the ocean world.
www.goldendolphin.com


----- Original Message -----
From: "Gary R. Boucher" <engineer@sport.rr.com>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, November 20, 2002 11:21 AM
Subject: Re: [PSUBS-MAILIST] Hydraulic Drive Unit


> Well, that may be so Mr. Starck.  However, lets think about some
things
> that you may have missed.
>
> (1) Unless the motor is completely outside the hull you will have
problems
> with directional thrust.
>
> (2) If the motor is inside the hull you have a thru-hull shaft seal to
> contend with of which, if it ruptured, you have a bad situation.
>       With hydraulics there must be two major breaches.
>
> (3) The motor will have to be reversible (not the case with hydraulics
> using a 4-way valve).
>
> (4) The bulk of the weight of the propulsion system can be more easily
> centered in the hull.
>
> (5) The hydraulic system can serve dual purposes in both propelling
the sub
> and furnishing hydraulic actuation to move heavy keel weights as in my
sub.
>
> (6) Pressure compensated motor compartments are a headache as they
require
> continuous air, or else a bladder to keep pressure away from the
seals.
>
> (7) Corrosion can be a major problem in motor housings that leak.
Just
> knowing that there is a leak requires special inspection.
>
> (8) The higher HP systems are easier to implement this way, because
> hydraulic motors are very compact and light weight per amount of power
> produced.  The bulk of the system can be located in-board.
>
>
> Gary Boucher
>
>
>
> At 06:10 PM 11/19/2002, you wrote:
> >Using an electric motor to drive a hydraulic pump that powers a
> >hydraulic motor to turn a propellor to  propel a sub is a really
> >complicated way of doing what could be much better done by using the
> >motor to turn the propellor directly.  The latter is far cheaper,
less
> >bulky, more reliable and more energy efficient.
> >
> >Hydraulics are a good way to distribute power especially where high
> >force is required but they consume a lot of energy in themselves and
> >offer no advantage in this application.
> >
> >Walter Starck
> >Golden Dolphin Video CD Magazine
> >The premiere publication of diving and the ocean world.
> >www.goldendolphin.com
>
>
>