Re: [PSUBS-MAILIST] Hydraulic Drive Unit

["Walter Starck" <wstarck@ozemail.com.au>]

Gary,

I don't have the time nor inclination to get into a pissing contest over
credentials.  I understood this thread to be about the putative merits
hydraulic driven propulsion for PSubs.  I offered the opinion this
approach offered no real advantage and considerable disadvantage as to
cost, total system bulk, complexity and efficiency.  I also said they
will work and work well but in view of the disadvantages they are not
the best solution.

Thus far your arguments for hydraulic propulsion are all hypotheticals
addressing non-problems while your objections to straight motor drives
are in regard to problems that in actual practice have been solved for
many years.  Literally thousands of  successful PSubs, ROVs, DPVs,
research submersibles and larger military and commercial submarines have
been built.  Only a tiny minority employ hydraulics for propulsion.
Propulsion system leakage and  reliability are rarely problems and in
those rare events are neither disasterous nor difficult to fix.

I am not familiar with your particular application and have no opinion
in that regard but as a general solution for PSubs which is what the
discussion seemed to be about, hydraulic propulsion would be a poor
choice.

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: Thursday, November 21, 2002 10:28 AM
Subject: Re: [PSUBS-MAILIST] Hydraulic Drive Unit


> Walter Starck wrote:
>
> >Gary Boucher wrote: " I get somewhat irritated when people that have
not
> >gone through this process sit back like armchair quarterbacks and
make
> >broad reaching
> >technical statements."
> >
> >I do too but with over 40 years experience in designing, building,
> >operating and maintaining a wide variety of underwater and marine
> >equipment I have gone through the process.
>
> I have no idea what your credentials are.  Forty years of "experience"
is
> pretty vague, but lets say that you have experience in actual design
and
> construction of manned submersible propulsion systems.  The issue that
I
> raised stands.  You are making a blanket condemnation of hydraulic
> propulsion and this is an uninformed declaration.
>
> >Alec Smythe Wrote: "In an earlier post Gary pointed out that in
> >hindsight, he recommends compensated trolling motors for their
> >simplicity."
>
> Lets set the record straight here.  I do recommend pressure
compensated
> trolling motors for most applications where people are designing
> PSUBS.  There is a simple reason for this.  It is the easiest approach
for
> the PSUBer who has limited knowledge of other approaches.  A thru-hull
> shaft is probably the very last thing I would recommend for these
> people.  I don't recommend hydraulics for every application.  I don't
> recommend hydraulic propulsion for most subs.
>
> You probably have no idea what the design philosophy of my sub is.
You
> have no idea what the intended purpose of my design was, or is.  You
are
> placing yourself in the position of an expert and basically saying
that all
> hydraulic propulsion is a bad idea.  I strongly disagree.
>
> If hydraulic propulsion is such a bad idea, why don't you take this
> campaign to the manufactures of thrusters that are driven by hydraulic
> fluid.  They are on the market.  They must sell because they still
make them.
>
> >This seems to agree completely with what I have said although Gary
now
> >seems to disagree.
>
> No, no change in my opinion.  The main reason that I would rethink my
> design if I had it to do again is weight.  I am marginal on my weight
and
> would for that reason like to have some extra buoyancy provided by
motor pods.
>
> >Sean Stevenson wrote: "For the homebuilder, overcoming the efficiency
> >issue is the only real hurdle for emplying a hydraulic system."
> >This like saying overcoming gravity is the only real hurdle to
building
> >a flying saucer.  High friction losses are inherent in hydraulics.
For
> >brief or intermittent operation or anywhere power is not limited this
> >loss may not be important.  In small submersibles however, available
> >power is a limiting factor and taking a 30% or more efficiency hit on
> >usage is an important consideration.
>
> I will quickly admit that efficiency can be an issue.  Whether this is
a
> deciding issue or not cannot be judged by anyone without first fully
> understanding what the design emphasis is.  Engineers learn very
quickly
> that nobody can build the perfect car, airplane, boat, submarine,
> etc.  Compare a Jaguar  to a Lincoln.  Each is an excellent car in its
own
> right.  Each has a totally different functional design, a totally
different
> purpose.  If fuel efficiency is your issue, buy a Taurus.
>
> Each design is an optimization of purpose based on a very extensive
set of
> tradeoffs.  The engineer's main purpose is to make judgements as to
what is
> important and what is not, what is going to promote the design
philosophy
> and what is not.  Good engineers are going to weigh the merits and
balance
> the pros and cons.
>
> I hear a lot of talk about propulsion on PSUBS.  I hear some really
> outlandish proposals.  Most are not feasible, but I seldom discard
these
> ideas, in that I put many of them on the shelf for later
consideration.
>
> >Carsten Standfuss obviously understands the issues.
>
> Carsten apparently is a good engineer and builder.  But, just because
he
> elected to not use hydraulics for his controls does not make, in
itself,
> hydraulic controls a poor decision.
>
>
> Gary Boucher
>
>