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Re: [PSUBS-MAILIST] Thrust from a pump?
Yeah, that's why I was curious about his boat's weight. I was trying to
visualise his sub/mass and apply the thruster concept to it. Hmmmm.
17 lbs. is sure low. That's about a bottom end MinnKota isn't it?
If it's a case of really good maneuvering taking into account (currents,
collision avoidance) more than just putzing around, I'd go MinnKota.
Currents are a bear up in our waters as they are in yours, I believe.
My ambient will have the pumps only because of Magical Child's light weight
(little internal volume) and large moment arms around the vertical axis. I
won't be doing any sidling in current to be sure. With the short moment
arms of the one-at subs, combined with their mass (and profiles), thrusters
would be more appropriate.
Rick L
----- Original Message -----
From: "Joseph Perkel" <joeperkel@hotmail.com>
To: <personal_submersibles@psubs.org>
Sent: Saturday, January 06, 2007 5:07 AM
Subject: Re: [PSUBS-MAILIST] Thrust from a pump?
> Hi Rick,
>
> Careful with the bilge pumps as maneuvering thrusters for a heavy manned
sub. If memory serves me correctly, your largest Rule pump is 8000 gph
against no external fluid resistance. That translates to 133 gpm. Cliff's
example was 200 gpm producing 17.7 lbf thrust through a 2'' tube (even
worse, your Rule through about 3/4"), .....that's pretty lightweight stuff.
>
> I think (yes, conjecture on my part) this all translates to.... nothing
beats the efficiency of the propeller.
>
> Joe
>
>
>
>
>
>
> --------------------------------------------------------------------------
----
>
> From: "Rick and Marcia" <empiricus@telus.net>
> Reply-To: personal_submersibles@psubs.org
> To: <personal_submersibles@psubs.org>
> Subject: Re: [PSUBS-MAILIST] Thrust from a pump?
> Date: Fri, 5 Jan 2007 22:26:08 -0800
> >Dismal as a main drive yes. For static maneuvering, no current, it
might
> >just do. A small child can exert just a little force to move a large
boat
> >away from a dock.
> >
> >For myself, it's pure conjecture at this point. I don't have personal
> >experience with this except with the kid part. If you take a look at a
> >bilge pump doing its thing, there really is a fair am't of water coming
out.
> >To be continued because I've considered this myself.
> >
> >Rick L
> >
> >
> > >
> > > ...Yes a very informative response. It's a wonderful thing how
mathematics
> >can prove / disprove a theory with such finality. I found the last line
> >summary interesting.....
> > >
> > > "As an example, a pump with a capacity of 200 gpm flowing through a
2”
> >duct would develop 17.7 lbf of thrust".
> > >
> > > If I understood this correctly, this is a pretty dismal way of
translating
> >energy into usable work. Kind of like a steam engine...a whole lot of
fire
> >for a bit of horsepower.
> > >
> > > Joe
> > >
> > >
> > >
> > >
> >
> --------------------------------------------------------------------------
> >----
> > > From: Cliff Redus <cliffordredus@sbcglobal.net>
> > > Reply-To: personal_submersibles@psubs.org
> > > To: personal_submersibles@psubs.org
> > > Subject: Re: [PSUBS-MAILIST] Thrust from a pump?
> > > Date: Wed, 3 Jan 2007 17:58:18 -0800 (PST)
> > >
> > >
> > > Alec,
> > >
> > >
> > >
> > > Below is a derivation of thrust that can be developed from a axial
flow
> >pump in terms of volumetric flowrate.
> > >
> > >
> > >
> > > The thrust due to accelerating fluid through a pump can be written
as
> > >
> > >
> > >
> > > F=M(V1-V0)
> > >
> > >
> > >
> > > Where M is the mass flow rate, V0 is the free stream velocity
upstream
> >of the pump and V1 is the velocity exiting the pump.
> > >
> > >
> > >
> > > But the mass flow rate M can be related to the volumetric flow
rate Q as
> > >
> > >
> > >
> > > M=Density*Q
> > >
> > >
> > >
> > > Substituting, the thrust in terms of volumetric flow rate is
> > >
> > >
> > >
> > > F=Density*Q(V1-V0)
> > >
> > >
> > >
> > > But the volumetric flow rate Q is related to velocity in the pump
duct
> >ID as
> > >
> > >
> > >
> > > Q=V1*A=V1*Pi*D^2/4
> > >
> > >
> > >
> > > Where D is the duct ID.
> > >
> > >
> > >
> > > Solving for V1, and substituting, the thrust can be written as
> > >
> > >
> > >
> > > F=Density*Q(Q/(Pi*D^2)-V0)
> > >
> > >
> > >
> > > For a thruster oriented approximately normal to the direction of
flow,
> >the inlet velocity can be assumed to be zero. The thrust then reduces
to
> > >
> > >
> > >
> > > F = 4*Density*Q^2/(Pi*D^2)
> > >
> > >
> > >
> > > Or
> > >
> > >
> > >
> > > F= 0.001766*(q/d)^2
> > >
> > >
> > >
> > > for freshwater where,
> > >
> > >
> > >
> > > F = Thrust, lbf
> > >
> > > q = pump volumetric flow rate in gpm
> > >
> > > d = pump outlet duct inside diameter in inches
> > >
> > >
> > >
> > > As an example, a pump with a capacity of 200 gpm flowing through a
2”
> >duct would develop 17.7 lbf of thrust.
> > >
> > > Cliff
> > >
> > >
> > > ----- Original Message ----
> > > From: "Smyth, Alec" <Alec.Smyth@compuware.com>
> > > To: personal_submersibles@psubs.org
> > > Sent: Wednesday, January 3, 2007 4:20:48 PM
> > > Subject: [PSUBS-MAILIST] Thrust from a pump?
> > >
> > >
> > > I'm contemplating using water pumps as maneuvering thrusters (NOT
for
> >main propulsion). Cousteau's socoupe used a hydraulic pump for the
jets, but
> >I'd like to avoid that route if possible due to the excessive noise. DC
> >submersible pumps are convenient but I haven't found anything beefy. I
could
> >try mating a trolling motor to a pump head. Submersible well pumps look
> >promising because they're very powerful yet compact, but they require
AC,
> >and I don't think I can reverse them so I'd need four pumps instead of
two.
> >I could of course hang trolling motors off the boat font and back, but
it
> >really messes up the hydrodynamics of what can otherwise be a quite
clean
> >design, and the props on my trolling motors make them too large to duct
into
> >the MBTs.
> > >
> > > Assuming I do settle on some kind of pump, the next question is
how
> >strong it needs to be. Does anyone know how to translate GPM (or LPM)
into
> >static thrust?
> > >
> > > Any ideas or experiences would be much appreciated.
> > >
> > >
> > >
> > > Thanks,
> > >
> > > Alec
> > >
> > > The contents of this e-mail are intended for the named addressee
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> > >
> > >
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