Hi Shaun,

Ive been reading up a bit on pumps, but some of the math is beyond me. i do
know that its possilb eo hook must pumps up either in series, or in
parallel. in parallel you quite logically get a doubling of flow in gallons
per hour or whatever, while in series you combine the 'heads' whatever that
means. i think it means head pressure?

Yep, head is pressure. Basically, you have one pound/sq.inch for each
27.68" of water column (height).

i know a lot of the losses in small pumps are from pumping 'up'.

That's kind of a misconception regarding 'head'. Pumping up, down, or
horizontal, the flowrate is dependent on the total backpressure on the
discharge line (but of course, 10' of vertical pipe does have more total
backpressure than 10' of horizontal pipe - of the same size).

most small
pumps are rated by how high they can pump water, and the rating for flow
goes down as the height increases. installed in a boat, i would try to keep
the whole thing on the level with the shortest hose runs possible. on a
beach cat, i would have a thru hull on the side of the hull with maybe 6
inches of hose going to the pump, then another foot of hose going to the
outlet.

Keeping the tubing runs as short as possible is certainly the right
approach to reduce frictional losses. One problem with the inlet on the
side of the hull (or any hull surface tangential to the water flow) is
that you get Bernoulli effects as the boat speed increases, that tends
to create a vacuum in the suction line (the same concept that makes
paint sprayers - the kind that use air hoses - or end-of-hose garden
sprayers work. The high speed stream across the diptube end creates
suction to raise the paint/roundup into the discharge stream).

i think youd have to start with two pumps in each hull, both running off a
common larger diameter inlest, and through a Y joiner to a common outlet.
this would give you some options. you could run the pumps in parallel, or
in series. then you would have to experiement with various reductions in
the outlet to see what the smallest diameter nozzle you could use without
losing flow would be. this is probably how you would use 'gearing'.

if you used too large of a diameter nozzle, you really wouldnt get any force
at all.

Don't confuse "velocity" with "Force". Just like with a garden hose
where you have, say 80psig, you can pinch the end to get a higher
velocity stream, but you get less flow (i.e. less mass). Since the
force = mass x acceleration, the force however is the same (you only
have 80psig to start with). The same is true for pumps, as you note
above, when you create more backpressure (pinching the hose), the
flowrate goes down. If you move 100gpm of water through the system, the
force is the same whether the discharge is 1" or 3", only the velocity
of the dischage changes. Remember, PSI is pounds per square inch (i.e.
force per unit area), so the 1" discharge stream may be at 10 times the
pressure of the 3" stream, but the 3" stream has 10 times the
cross-sectional area of the 1" stream.


Keith Hughes