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
> >
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> >
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