Thank you - I’m intrigued by the description of your design, but not entirely sure I can fully visualise it (at least, the second part about the bowl-shaped piston). Have you any diagrams or photographs?
Along these lines, though planing comes into play on these, on a rowboat I had a 8 hp motor can get up to IIRC 20 mph, and using a 25 hp motor gets it up to 30mph.
No. Picture a stack of two 16in bowls laid sideways. One is the piston and the other is the “cylinder/hemi cylinder head”. Picture a membrane molded between them attached at the centre to the center of the piston and at the rim attached like a drum skin to the “cylinder”.
This essentially encloses a watertight volume with either negative or positive pressures depending on the stroke , opening or closing the bowls.
The back of the seat which is on a rowers seat track is attached to the piston. The cylinder is firmly attached to the kayak and a single discharge port which runs into a dual checkvalve chamber responding to the negative and positive pressures.
Theoretically, the maximum stroke should equal double the depth of the bowl given the membrane though flexible should not stretch otherwise a lot of energy would be wasted.
Essentially an overly large diaphram pump.
Sorry, but that seems to be the best I can do at the moment
That’s not a Hyak, THIS is the Hyak.
Planing comes into play if you have a planing hull. A lot of row boats do have that kind of hull.
But a kayak hull won’t plane any more than a cruise ship because they have displacement hulls not intended for planing.
There is also the concept of hull speed based on the waterline length of the boat where resistance drammatically increases. It just so happens that for a 17 foot kayak or canoe, that happens to be about 6 mph or the same speed as the canoe powered by the jet. The canoe in the video appears to be longer than that though so I don’t think that needs to be considered.
Thanks - that makes a lot more sense now.
As I mentioned above though, I think there might be an inherent inefficiency in any pump that operates an alternating suck-blow cycle - in that you are expending energy on the inhalation stroke, none of which is preserved for the exhalation. (as opposed to an impeller or continuous rotary pump, where the action of drawing in the fluid is the same as that expelling it.
To be clear the inhalation stroke is provided for by the bungee that was stretched during the exhalation stroke.
Of course I expected some considerable inefficiency with the pump, but I was looking to paddling as a standard and I believe that the simple power generated by pushing with your legs against a fixed object while your ass and back are firmly restrained has to be way more efficient and comfortable than operating a lever with your arms, to deliver energy and power. Perhaps enough to compensate or over compensate.
Another way to look at arm power to leg power is by comparing the exercise of knee bends to push ups . The former is far easier and the latter can’t even take advantage of the benefit of much less weight to raise.
That isn’t a great comparison since a pushup is all arms, but a proper and efficient kayak-paddle stroke actually does involve considerable back and abdominal muscles, and even some leg muscles. Of course, if it’s a beginner with poor technique and/or someone in an ill-fitting kayak with poor foot/leg/hip bracing and a high seat-back, then that’s mostly arm muscles doing the work.
And a knee bend is all legs.
Granted, The torso does move the shoulders back and forth in kayak paddling especially racing, but the legs merely brace.
We can also compare standing on your feet to hanging by the hands to a chin up bar or doing a hand stand.
Of course neither is a perfect comparison.
I’ve reread this, and you seem to be talking about a mechanism similar to a rowing machine for driving the pump. Both legs pumping together, and potentially arms could be but to use as well. The regulator concept should allow a somewhat smooth output if enough air pressure can be built up. You might need a second chamber with a pressure activated valve to maintain constant output. Connecting this mechanism to a turbine could be problematic, because unlike pedaling, you’re driving with an intemittent force. A turbine could charge a pressurized chamber also, but positive displacement pumps should be much more efficient at that.
It sounds like the big problem is the slow cycle, requiring a large piston because of the time between because of the long cycle time. One solution would be to use gears or pulleys to operate a much smaller pump at higher speed. On the return stroke you could use an energy storage device (bungee cord) so that the forward stroke continues to operate the pump, or count on the compressed air to maintain pressure. The bungee cord approach means an efficiency loss to recover the energy. You could also use your arms to provide action on the forward stroke. Less energy than your legs could produce from pushing though. Probably a combination of arm driven return and bungee cord energy storage would be optimal and allow continuous motion. Several types of linkages could be used to drive a pump at constant speed.
Assuming the sliding seat on a track mechanism isn’t a problem, I think gearing (or pulleys) to drive a smaller pump faster is the solution. A mechanism that delivers continuous force will probably be more efficient though, and allow a turbine solution. Turbines also have a flywheel effect, so the output is steady, and the compressed air regulating chamber could be much smaller, or eliminated.
How far did you get with the sliding seat mechanism? Once you have that, it shouldn’t be that hard to try connecting different mechanisms. As you’ve found already, building pumps can be difficult, but their ought to be some existing products that could be integrated. I recently saw some type of radial pump (probably some form of vane pump) made of plastic that claimed to drive a considerable flow from hand cranking.
Also, any water output from a pump or turbine is likely to be moving too fast. Optimally, the outflow speed is equal to your forward speed, meaning a large volume of slow moving water. But you can use an augmenter to rectify that. In simple terms, your outlet pipe is inside of a larger pipe open at both ends. The high speed output accelerates a larger volume of water, something like a venturi pump. This works well with air which is compressible, not sure how well it works in water though.
Anyway, don’t give up. Just keep refining. You may hit upon the right solution at some point.
I don’t think that makes a difference - a pump with an alternate inhale/exhale cycle needs to do more work than a pump with a continuous flow, for the same volume of water - and that work needs to come from somewhere.