Any opinions on the feasibility of foot-operated water jet propulson for a
small boat like a canoe or kayak? I was thinking of mounting twin water
pumps on the (out)sides of the hull to suck water in the front of the
pumps and squirt it out the back through a smaller diameter pipe to make a
jet stream. The water pumps would be foot operated through levers and a
pivot. Got the idea from reading a book on ancient Roman engineering.
Could the legs and water jets produce enough propulsion to move the boat
at, say, walking speed? I think a separate pump on each side, powered
independently by the two legs, would allow the operator to steer the boat
by pumping one harder than the other to turn.

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William R. Watt wrote:
Any opinions on the feasibility of foot-operated water jet propulson for a
small boat like a canoe or kayak? I was thinking of mounting twin water
pumps on the (out)sides of the hull to suck water in the front of the
pumps and squirt it out the back through a smaller diameter pipe to make a
jet stream. The water pumps would be foot operated through levers and a
pivot. Got the idea from reading a book on ancient Roman engineering.
Could the legs and water jets produce enough propulsion to move the boat
at, say, walking speed? I think a separate pump on each side, powered
independently by the two legs, would allow the operator to steer the boat
by pumping one harder than the other to turn.

That's what paddles are for. Simple, elegant, effective engineering. I
don't understand why people are constantly trying to "update" the basic
design of these elegant craft with "Rube Goldberg" mechanical
mechanisms. A large part of the beauty of these boats lies in their
simplicity and the connection that the paddler has with the water. To
eliminate that is to change the very nature of the boat.

While your idea could certainly propel the boat, there are at least two
problems with it. First, the operator would still need to carry a
paddle, as it's necessary for turning and in the case of a kayak, for
bracing and rolling. Second, your system would not work for anything but
the gentlest of turns except perhaps on a really short boat. There
simply wouldn't be enough of a lever arm to cause the boat to turn abruptly.

That's what paddles are for. Simple, elegant, effective engineering. I
don't understand why people are constantly trying to "update" the basic
design of these elegant craft with "Rube Goldberg" mechanical
mechanisms. A large part of the beauty of these boats lies in their
simplicity and the connection that the paddler has with the water. To
eliminate that is to change the very nature of the boat.

Mostly for hands free operation for taking snapshots or videos.
But alas, also because upper body muscles put a greater strain on the
heart for the wame amount of power than the lower body. It has something
to do with the upper body muscles being smaller and closer to the heart.
After a heart attack they encourage you to walk and discourage lifting.


While your idea could certainly propel the boat, there are at least two
problems with it. First, the operator would still need to carry a
paddle, as it's necessary for turning and in the case of a kayak, for
bracing and rolling. Second, your system would not work for anything but
the gentlest of turns except perhaps on a really short boat. There
simply wouldn't be enough of a lever arm to cause the boat to turn abruptly.

I can turn the boats fine with a small sail and no rudder or paddle,
adjusting sail postition and shifting weigth to adjust boat trim, but
there is the daggerboard to pivot on.

My main concern is the amount of propulsion that could be provided by foot
operated water pumps. I imagine a slow pump action, using, say 3" plastic
drain pipe for the pump body. I'll guess have to get out the college physics
text and try some calcultations. Anything I should take into consideration?

An earlier idea was separately operated foot paddles, like paddle wheels
but without the wheel protruding below the hull, so the paddles would be
raised out of the water at some point in their rotation, allowing the boat
to drift into shallow water. Also the paddles could be rotated
independently in either direction making turning easier, as is done with
oars. But the linkages, etc. I can imagine would be heavy and awkward. The
foot operated pumps I can imagine would be simpler.


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Have you considered the idea of using foot-operated paddlewheels
instead? It would seem to me that they would give you better propulsion
for the same amount of effort. Also, I would think that they would
actually be easier to build and maintain. You could have 2 wheels (1
each side) and have them set up to mount on top of the gunwales. They'd
be nice and quiet too, for those nature pix that you might want to
capture with your camera.

Hope this helps,
Paul

Willliam,
Consider the basic principle that thrust = mass x velocity, but power
consumption is proportional to !/2MV2.
This means that while a small jet at twice the speed has the same thrust as
the larger jet at twice the area, the power consumption is four times
greater!
Big Slow Pumps!
For anyway near the same effectiveness the jet area needs to be around the
blade area of an oar.

Regards barry lawson

"William R. Watt" wrote in message
...

My main concern is the amount of propulsion that could be provided by foot
operated water pumps. I imagine a slow pump action, using, say 3" plastic
drain pipe for the pump body. I'll guess have to get out the college
physics
text and try some calcultations. Anything I should take into
consideration?

Hmmm... thrust - drag = mass X acceleration

Brian Whatcott

On Wed, 19 Oct 2005 07:04:02 +1000, "barry lawson"
wrote:

Willliam,
Consider the basic principle that thrust = mass x velocity, but power
consumption is proportional to !/2MV2.
This means that while a small jet at twice the speed has the same thrust as
the larger jet at twice the area, the power consumption is four times
greater!
Big Slow Pumps!
For anyway near the same effectiveness the jet area needs to be around the
blade area of an oar.

Regards barry lawson

"William R. Watt" wrote in message
...

My main concern is the amount of propulsion that could be provided by foot
operated water pumps. I imagine a slow pump action, using, say 3" plastic
drain pipe for the pump body. I'll guess have to get out the college
physics
text and try some calcultations. Anything I should take into
consideration?

Yeah, but the efficient process is the one most nearly reversible. Minimize
turbulence and velocity change.

Roger

http://home.earthlink.net/~derbyrm

"Brian Whatcott" wrote in message
...
Hmmm... thrust - drag = mass X acceleration

Brian Whatcott

On Wed, 19 Oct 2005 07:04:02 +1000, "barry lawson"
wrote:

Willliam,
Consider the basic principle that thrust = mass x velocity, but power
consumption is proportional to !/2MV2.
This means that while a small jet at twice the speed has the same thrust
as
the larger jet at twice the area, the power consumption is four times
greater!
Big Slow Pumps!
For anyway near the same effectiveness the jet area needs to be around the
blade area of an oar.

Regards barry lawson

"William R. Watt" wrote in message
...

My main concern is the amount of propulsion that could be provided by
foot
operated water pumps. I imagine a slow pump action, using, say 3"
plastic
drain pipe for the pump body. I'll guess have to get out the college
physics
text and try some calcultations. Anything I should take into
consideration?

William R. Watt wrote:

Mostly for hands free operation for taking snapshots or videos.

That makes sense.

But alas, also because upper body muscles put a greater strain on the
heart for the wame amount of power than the lower body. It has something
to do with the upper body muscles being smaller and closer to the heart.

I'm afraid you're baseing your design on a false premise. The small
muscle groups of the upper body are not capable of driving the heart to
as high a rate as the large lower body muscles. I'm also an avid cyclist
and can tell you from experience that paddling is far easier on the
cardiovascular system than cycling is. With the exception of high
intensity paddling while surfing or playing in rocks, I never even get
winded while paddling. By comparison, I can drive my heartrate into the
high 180's on a bike.

It's not even remotely possible to generate the same amount of power
with the upper body muscles as with the lower body muscles, which is why
they cannot drive the heart rate as high. It's also why kayak racers use
boats that allow them to rotate at the hips using the legs to help drive
the boat.

After a heart attack they encourage you to walk and discourage lifting.

That's because straining to lift something increases blood pressure,
especially if you bend over to do it.

Thanks for all the suggestions.

You can get more power from the lower body (the muscles are larger) but
for the *same* amount of power the upper body puts more strain on the
heart. That's what I read while researching heart disease.

I have worked before with hull resistance figures for canoes and kayaks.
You can get a pretty good estimate of the horpower required to move a hull
at a certain speed. Non-athlete paddlers can sustain about 1/20 of a
horsepower. It's also easy to calculate the amount of water pumped from
the size of the cylinder and the rate of pumping. It's possible to convert
the amount of foot pressure on the pump into the speed of the water
leaving the pump. I should find out about the efficiency of water pump
propulsion. In one book I was lookign at last night it says the shape of
the outlet nozzel is important. I once estimated the energy comsumption
efficiency of paddling a canoe at about 13% (it's on my website under
"Boats").

I agree with one poster that innovation is the fun part about designing
and bulding boats. But I'm not crazy about the building part,
time-consuming messy physical work costing money, so I try to do as many
calculations as possible before starting to build, even though trying to
figure out the formulae sometimes drives me crazy.

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Foot operated pumps for propulsion don't look practical. They would be too
inefficient and they would only move the boat forward.

The device on the Hobie kayaks is amazing. With all the propulsion under
the hull there is no waste in surface turbulence. However it is
disappointing that it's only 10% more energy efficient than arm
propulsion. I thought it would be less of a strain on the heart. I can
imagine two improvements but don't know if they would be feasible.

First, as the desinger points out, reciprocating leg action is better than
circular leg action, but it would be even better if the action were low
instead of high. Perhaps the cranks could bent over or inverted.

Second, the fins only move the boat forward. If the fins could rotate they
could be aimed in any direction like an outboard motor to steer the boat,
and to propel it backwards.



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