Jet, Jet Pump, Waterjet, Jet Drive vs Prop

[brian eiland]

I know of a gentleman who use to work with this military technogy...I'll try and get his attention, comments, etc.

Meanwhile I thought I would link these discussions to this subject thread as there is considerable talk of variable inlet conditions.
Help me understand the limitations of a jet pump in a planing hull.

[larkinja]

I don't know if this would be the appropriate place for this but here goes...

I would like to build my own kayak/canoe type boat with my son. The idea would be pedal driven. I know commercial boats of this type exist, but they either have a propeller below the hull, or crazy, inefficient fin looking things hanging down. Neither of these designs would work in a shallow river setting. I have seen people mount two paddle wheels to either side, but seems that would make a ton of splashing and noise. Kinda ruins the idea of a peaceful scenic float down the river.

The only concept I have seen so far that interests me is a prop on the end of a 1/4 sprung steel shaft trailing behind the boat. It just seems like one more thing to get caught up on a log in the river.

My question that makes this relate-able to this topic is whether or not a jet drive type system could be used considering the relative low power of human pedaling. The idea would be to build a passageway into the hull of the kayak where water could be picked up towards the front. This would keep a spinning propeller away from rocks, sticks, and other river debris. Obviously some sort of screen would have to be used to keep it out of the passageway. Steering I believe could be as simple as a flexible hose at the end, or even just a simple rudder, other that the inevitable shallow water not allowing for enough rudder in the water to work.

Now my jet drive system, I don't mean anything commercially available. I mean a small set of propellers on a shaft with a couple u-joints inside a pvc tube or something similar. Something that could be hand made. I have a fair amount of metal fabrication experience, and some fiberglass experience. Probably just enough to get me in trouble .

Anyone have any thoughts as to whether or not something like this could work, or if you have any suggestions. Keep in mind I own boats, but have never even considered building one. I've been on plenty of kayaks and canoes though. I would be replicating that design, or even modifying an existing one. Although sounds more fun to build from scratch.

[Submarine Tom]

larkinja,

Sure it would work. How well, I have no idea.

Check this out: http://www.mokai.com/

-Tom

[larkinja]

That is pretty cool. That is exactly the idea, except leg powered. Obviously doesn't need to go that fast. The idea is more to replicate the speed of paddling, with a little less work. A leisurely pedal would be a lot easier than paddling I think.

[brian eiland]

Originally Posted by larkinja

That is pretty cool. That is exactly the idea, except leg powered. Obviously doesn't need to go that fast. The idea is more to replicate the speed of paddling, with a little less work. A leisurely pedal would be a lot easier than paddling I think.

I believe you would find much more info on you subject if you were to "search button' the subject pedal power:
Pedal Powered Boats

best propolution method, normal Prop, Jet style or paddle wheel?

Human Powered Boat

Twisted belt/chain drives

Pedal Boat Design

...there is more

[larkinja]

I've been searching the forums, but I am still having some trouble finding relatable material. Most posts refer to larger boats or engine power.

[Submarine Tom]

I can tell you a few things:

You're not going to produce more than 100 - 120 watts at a "leisurely" pace. That's ~1/7 of a horse power. You'll need a pretty efficient means of energy transfer and a low hull resistance to get any sort of speed at all.

Good luck.

-Tom

[baeckmo]

......and with the limitation that Tom points out, there is only one way of getting a decent propulsion efficiency; use an open propeller with low blade loading!!!!

[beewee]

I am not sure if this technology is licensable just for them?

Are there not already many companies making hubless pod systems, although usually on larger low speed craft.

Seems that Green Samba has is a hubless pod system thats been tweaked to turn it into a jet pump. Tweaking means giving it a heap of power, ducting the thrust, maximising the prop efficiency for its high speed use ... like any jet pump system.

I have in fact heard of other companies that manufacturer small hubless pods, usually for small submersibles used in the oil industry.

[larkinja]

The pedal kayak from Native seems to cruise right along with what seems to minimal effort. THe only problem is that the prop is under the boat. Won't work in a river. I guess the questions comes down to this. If the Native kayak's setup were enclosed in the hull, ie similar to a jet, maybe two inlets one on each side to assure enough water intake, how dramatically would it change the efficiency. If it even went half the speed of the videos I've seen of the native, I would be happy.

I can probably figure on the fact that it might not be as efficient as a open prop in the water. I live in Michigan, and the rivers around here are loaded with fallen trees, rocks, stumps, etc.. I see even a prop on a sprung shaft having difficulties.

Some things I am keeping in mind is that this would be for down river use only. Doesn't need to fight the current. If you consider the minimum amount of paddling needed to navigate turns in the river, and keep a slow pace during areas of low current, this is all it would need to do. Really, the only idea is to free up my hands for picture taking, maybe fishing, and not having to hold a paddle the whole time. Every time I try to take a picture of something, I get interrupted by the fact I have to grab the paddle and make some adjustments so I don't end up in a tree. I just see the whole thing being much more relaxing without a paddle. I don't see using this in a lake. I have power boats for that. This more for the quiet Sunday float down the river.

If you guys still think it won't work after this, then maybe it just isn't worth it. Thanks again for your insight.

Jason

[Submarine Tom]

Interesting. So how will you steer away from the tree without using your camera occupied hands?

[beewee]

Just looking at the statement of the craft being able to provide 65hp from the two pods that effectively gives it 250hp in petrol standards. I see that in fact simpler, lighter 135hp Jetski can do 65mph with about 900lbs of thrust.

The Green Samba is much lighter, so will need less thrust to get to 65lbs, I am not sure how much, but even if you half it to about 500lbs that means each pod must be producing about 250lbs each?

That is an incredible feat. With normal technology it just wouldn't be abel to produce that sort of power without huge batteries ... can hubless technology really be that efficient?

Will be interesting to see how their prototype goes

[larkinja]

Originally Posted by Submarine Tom

Interesting. So how will you steer away from the tree without using your camera occupied hands?

If it steered in a similar fashion to a jet ski, then a push pull dual lever system could steer it. One on each side. Of course you would need a hand for that, but somehow I don't think comparing pushing a lever for a little steering hardly compares to some hard paddling on one side to make a turn. In this theory one hand could steer. Not sure it would be so easy to use a paddle with one hand.

[Submarine Tom]

Oooooh, I see.

-Tom

[brian eiland]

Originally Posted by larkinja

I've been searching the forums, but I am still having some trouble finding relatable material. Most posts refer to larger boats or engine power.

Have a look at the posts by this member "Guest625101138"

For instance go to this subject thread and hit his name, then find all post by him.

He use to post under another name, so I didn't find him right away. I think you will find his material real interesting