Re: [PSUBS-MAILIST] Hydraulic Drive Unit

["Gary R. Boucher" <engineer@sport.rr.com>]

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