Re: [PSUBS-MAILIST] Hydraulic Drive Unit

[Ray Keefer <Ray.Keefer@Sun.COM>]

Hi Carl,

I am one of the ignorant ones also. That is why I host this site. To
learn from others, whether they are credentialed by experience or schooling,
I don't care.

But every tid bit I hear about I weigh and judge for usefulness in my
projects. I am responsible for my final design. I like hearing about
other's concepts however the designs I will come up with will have
elements that fit my need, and mine only.

Regards,
Ray

> Date: Thu, 21 Nov 2002 00:31:50 -0700
> From: Coalbunny <coalbunny@vcn.com>
> X-Accept-Language: en
> To: personal_submersibles@psubs.org
> Subject: Re: [PSUBS-MAILIST] Hydraulic Drive Unit
> Content-Transfer-Encoding: 7bit
> 
> 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
> > >
> > >
> 
> -- 
> "You delight not in a city's seven or seventy wonders, but in an answer
> it gives to a question of yours, or the question it asks you, forcing
> you to answer, like Thebes through the mouth of the Sphinx." -- Kublai
> Khan