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?

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

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.

Shaun



Keith, I think you're missing a factor here. "Displaced" implies a
DISTANCE per unit time. That's where horsepower (Or any other POWER
unit) matters. 550 FOOT - (Pounds-Force) (Per SECOND) means that you
could "Gear Down" (or use other force multiplication arrangements) and
lift 550 pounds at 1 foot per second, or instead lift 55 pounds at 10
feet per second. Right?

A large diameter 4-blade prop on a 60 foot boat with a small pitch and
a 20 HP diesel with a reduction gear can put a (lot) of FORCE on that
boat and move it at 5 or 6 knots. I've seen an old 20 Hp Mercury
outboard push a 3-point Hydro at over 40 MPH.

We don't know enough here (yet) to say what the efficiency of an
inboard pump would be in moving a small boat against it's frictional
resistance at a certain speed. We all know, from experience, that
moving a small boat like the Hobie mentioned at the beginning of this
thread takes VERY little force at very small speeds. A gentle push by
hand moves it right away from the dock. Most of us have moved a 10
meter or larger boat a few feet by leaning a little on a dockline.

What we're missing is some approximation of the efficiency of a well-
designed pump in converting electrical power to mechanical power to
move a boat. I think we'd have to do some research and talk to some
mechanical engineers who understand pumps! I have a friend who
recently built a small Hydroelectric plant in New York, who did his
own calculations and is using a large (Thing formerly sold as a pump)
as a turbine, with excellent efficiency. He's running 2 typical homes
on it.. It's a BIG pump and he's at the bottom of a 85 foot
waterfall...

Someone somewhere knows a lot more about propelling a boat with an
inboard pump than I do!