Re: [PSUBS-MAILIST] Hydraulic Drive Unit

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

Carl

      That was never my intention in anything I wrote here, to say that if 
you don't have some sort of credentials you should not be here or build a 
sub.  I hope you didn't read that from anything I said.  I would also get 
caught in that one.  My doctorate in engineering is not in mechanical.  I 
do not even have a BS in mechanical engineering.    The best credentials I 
can offer would be the fact that I have done it, at least once.  I have 
gone through the design and construction of a completely successful sub, a 
sub that does exactly what it was designed to do.
      If I may, I would like to tell you more about my design and why I did 
some of the things I did.  Most everyone that builds a small sub 
concentrates on high visibility, accepts the expected slow speeds, and 
tries for max duration.  This was not my design philosophy at all.  I 
wanted to built a sub for the pure enjoyment of driving it.  I did not 
concentrate on vision as I have only 5 windows and they are all on the 
sail.  I did not want outside battery pods as I wanted the boat to look and 
feel more like a traditional U-Boat, long and sleek.  I did not want to use 
dive planes, but have the capability of obtaining a fairly steep pitch nose 
up or down.  And last but not least, I wanted speed!  I wanted enough HP to 
drive the boat at a speed that would give some sensation similar to 
conventional subs.
     Because of the ballast tank arrangement fore and aft, I did not choose 
to use a drive shaft running through the hull.  I wanted the power to 
originate behind the rear ballast tank.  Not having unlimited funds, I 
could not go out and purchase thrusters or opt for some motor combination 
that would have cost me thousands of dollars.  I had to design within my 
limits both physical and monetary.  I was interested in trolling motors, 
but cost of multiple motors, pressure compensation, and the lack of thrust 
in most models deterred me from that choice.  Believe me I looked!
     I had to have a great deal of thrust for what I wanted to do.  I was 
not interested in duration.  As a matter of fact I have never even used a 
scrubber on board.  My longest dive to date is about 30 minutes.I was not 
overly concerned with efficiency as this was not a primary objective.
     When you study propellers you will find that the thrust a propeller 
produces is related to many factors, one of which is inflow velocity.  If 
you do not know the drag numbers for a specific sub, it is easy to 
miscalculate propeller match to a motor.  One thing that hydraulic drive 
allowed is the ability to change the displacement of the motor to better 
match the boats performance, not to mention solving many problems with 
outboard motors in housings and thru-hull electrical interfaces.  Mismatch 
of a motor-propeller combination in torque and RPM can result in low 
efficiency in itself.  As it turned out my best educated guess was good and 
I have not had to change hydraulic motor displacement.
     Also, because of the fore mentioned pitch control, I needed a large 
hydraulic cylinder to move a heavy weight in a track along the keel.  I 
would have had to employ rather robust hydraulics with or without the 
propulsion.


Gary Boucher



At 01:31 AM 11/21/2002, you wrote:
>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