Re: [PSUBS-MAILIST] Hydraulic Drive Unit

[Coalbunny <coalbunny@vcn.com>]

I come here because I like the idea of mini subs.  I guess us
non-credentialed folk ain't got no business here then.
Carl


Walter Starck wrote:
> 
> 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
> >
> >

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