I'm new here

Hi, I just registered yesterday; this is my first post.
I was looking for a forum about human power, and can't find one -- should be under "propulsion," I thought.

I have a real toad of a rowboat that I'd like to modify so I could sit facing forwards, and I'm thinking of an add-on assembly that would drive it with fishtail fins or moving foils. I have some rough ideas on how.

So, what forum is the right one for this? If I put it in Collaboration, what would that mean? I'm not interested in patents, marketing, etc., just want to make a one-off for myself.

Let me know,
Curtis

 

Welcome to bd.net, Curtis, and yes you are in the right place

Suggestions from the many members who have already built HPVs are surely coming.

In the meantime, give the Search > Advanced feature (third from right on the blue toolbar at the top of the thread) a try, some interesting discussions on this topic have been festering for a few years.

 

Thanks, I'll try that . . . might get an answer before I even ask the question

 

Curtis
I started this thread for such questions:
http://boatdesign.net/forums/showthread.php?t=23345
Irrespective you have started thread here.

There is some debate over the efficiency of flapping devices. I did a lot of experimentation with them as I felt nature had something to offer. I got close to the theoretical maximum possible efficiency under certain conditions. Kept trying until an observer pointed out that nature has not developed a shaft capable of continuous operation so cannot produce a propeller. I guess if flappers were really that good you would see modern aircraft using flapping wings instead of jets.

The Hobie mirage is a very clever system:
http://www.hobiecat.com.au/support/kayaks/miragedrive.html
The best thing about them is their marketing hype. In reality they give efficiency around 30% with low power and up to 50% at high power. With a heavy boat they would be even worse.

Flapping systems that are surface exposed are less efficient because the foil constantly ventilate. Here is the most developed version I know:
http://www.tailboats.com/propulsion_technology.html

Here is my oscillating foil boat:
http://boatdesign.net/forums/attachment.php?attachmentid=22566&d=1213860730
It is very efficient to 8kph before the boats starts bouncing badly. This speed is almost ideal for operation at 60rpm. It is a nice system for a boat with a large waterplane and reasonably heavy. I can give you design parameters for this.

Here are more flappers:
http://boatdesign.net/forums/showthread.php?t=21025&highlight=oscillating

THe most flexible and efficient set up is a prop. I can help you design a system if you want to try this.

So something to think about.

Rick W.

 

Rick,
Thanks for the input so far. I'll have to get back with the long list of limitations and other particulars; don't have time for it all now.

I've been looking at this topic for quite a while; thought I'd seen it all until I found this forum, but there isn't much here that's new to me, either. Still, I'll state my case presently. I've got to get ready to bring my Mom home from the nursing home tomorrow, so it may be a couple days.

peace,
Curtis

 

Here we go . . .

Okay, well, this is going to take a while, so please bear with me.

First, a little personal history is needed to explain some of the requirements that follow.

Several years back, my hip became arthritic. When the hip went south, it took my lower back with it. I now walk with a cane.

Bottom line: I don't bend in the middle very well. That is one of the reasons I'm in my present situation, and why I'm here seeking feedback.

Previously, I had an Ocean Kayak Scrambler that I was perfectly happy with. After the hip went bad, I could not safely get in or out of it, had no place to stash my cane securely, and couldn't even sit comfortably in it. Also, I found that I could no longer even get the boat onto the top of my car unassisted (I now have a pickup truck).

I sold the 'yak, but was determined to get on the water somehow. I needed a boat that was small and light enough to wrangle into my truck, and stable enough for me to get in and out of safely. Short, wide, light, flat bottom. A dinghy. I bought the smallest, lightest, (and cheapest) one I could find, this:

http://plasticboats.com/

It is 7.5 ft long and about 4 ft wide overall, weighs 50 lbs. I weigh about 160.

Oh, btw, before I got the Bathtub, er, Backwater, I designed a boat for my own requirements, and built a successful quarter-scale model of it, but figured out that I could not build the full-size version by myself, and shelved that notion (before I spent $$$ on material, thankfully).

Anyway, so far, so good. I'm back on the water. I can drag the boat to the truck and hoist one end onto the tailgate and shove it up on. It needed a modification to improve tracking, so I built a kick-up stabilizer, like a rudder, except that it doesn't turn. As to performance, well, you can guess from the pictures (more to follow). It will never be fast, but I don't care; I'm just out to enjoy being on the water.

Rowing is okay with me; I've always liked getting places under my own power, but I don't like going backwards. My neck is stiff from an old whiplash injury, so it's difficult and painful for me to look over my shoulder. A bicycle mirror helps some, clipped onto my glasses. I've looked at every forward-facing rowing device there is; they're mostly outrageously expensive, and I'm not sure how well they'd work with the boat that I have.

Since my hip doesn't work, anything with pedals is out of the question. I used to love bicycling, and had to give that up, so it's down to arm power.

To summarize, I have a boat that works for me; it accommodates my limitations. I'd just like to work it a little differently.

Now, then . . . (which is it -- now, or then?) . . . how'd I wind up here?

A lot of things on the internet catch my interest, and one of them was the topic of ornithopters. About half a year ago, I found the forum at ornithopter.org, and looked around quite a bit. What really got me excited was the work being done by Kjell Dahlberg. I saw his videos and models of boats propelled by various flapping foils, and thought that this might be a solution to my quest: a retrofit for my existing boat; something I could make inexpensively at home, and would do what I wanted done.

The configuration I liked best and focused on is that of two vertical foils. This has been demonstrated by Kjell and others, so we know it works, and it's especially amenable to a simple application of arm leverage. Also, with a proper drivetrain design, it can serve as forward propulsion, steering, and brake. Elegant. (See drawings.)

I know that the drawback of this is inefficiency, but that doesn't bother me. The shape of my rowboat is already inefficient, and I'm never in a hurry to get anyplace with it.

More to come . . .

 

. . . continued

I didn't stop with pitching foils; I continued to look for other possibilities that might be better. One link sent me to the work of Kevin Jones:

http://aa.nps.edu/~jones/

which sent me in at least two new directions. One of those was the "Schmidt wave propellor," and the other was -- eventually -- to the Trampofoil (now "AquaSkipper").

And this is where I am now.

First, look at:

http://aa.nps.edu/~jones/publications/aiaa97-0826/

and open the PDF at the bottom. Figure 3 shows the Schmidt wave propellor, but notice what it says in the paragraph just above: "Obvious mechanical difficulties arise from pure plunging motions . . ."

"Obvious mechanical difficulties" -- ? Now, I don't pretend to be able to follow the math on these pages, and some of the physics is a little above my head (by only a few fathoms or so), but I don't see any mechanical difficulty at all in using my arms and a simple lever to create a nearly pure linear oscillation. And I get free extra thrust from a second, stationary foil? I've been moving my arms already anyway! Where do I sign up??!

Now, back to the Trampofoil for a moment. Check this out:

http://www.instructables.com/id/SP3EGW1F2297BYM/

They show you how to make one of your own, and they seem to have stolen the measurements straight off the high-priced production model. The main wing is 87.25" long (span) x 5.5" wide (chord), which gives an aspect ratio of 15.86, and the make-it-yourself folks seem to think that just about any profile will perform. Jones' studies seem mostly to deal with NACA 0012 profiles.

The AquaSkipper page has cheerfully given up the secret to the device's operation, namely, a very slight pitch change coupled to the plunging motion -- the very same combination that keeps popping up in Jones' papers.

I haven't developed that idea very much yet, but it isn't complicated at all. The drawback with it is that it needs a separate rudder.

So . . . here's where you folks come into the picture.

If I go with the first idea, I need help figuring out the size and shape of the fins. I suspect that I could cut the back ends off of a pair of ordinary swim-fins and attach them and they might just work, but I'm not sure. They may need a peduncle, and if so, how long? Also, how deep should they be below the surface?

As to the second idea, it hasn't aged much in my head yet, so I don't have a lot of specific questions so far. One thing I noticed from Jones' work is that the pitch changes are quite small, about plus-or-minus 5%. I thought that a bit more (user variable as needed) might be good for getting it moving from a standing start, but it seems to me that very little is needed once you are up to speed. This might be thought of as a kind of trim control, and may be adaptable for reverse thrust (not that my boat really needs much help slowing down).

Anyway, that's about it for now. Let the fun begin!

Cheers,
Curtis

 

Curtis
Here is a starting idea. It consists of a flapping foil that works under the boat and is activated by a hand crank. The whole thing could be dropped into place using wing nuts to lock it down. The blade would sweep through about 500mm.

Making the crank would be the most difficult part. I have not shown this but it would require a shaft running across the boat with hand grips on crank arms off the shaft. THis would be decidedly more efficient and controlled than rowing.

There is some detail not shown but it is not too hard to make. The wheels shown at the side would not need to be wheels either; just arms but the wheel shows the path. There are ways to engineer this to go reverse but it will lose a bit of efficiency. You would need a rudder of some sort to steer. This would usually be foot controlled.

You could go to a half size foil on each side and decouple the blades but the action would not be as smooth. There are many variations on this.

You should not rule out the possibility of a prop either.

There are also forward facing rowers.

I have made a swing arm drive that is a much friendlier pedal motion than cycling. Attached video is a demonstration of the swing arm pedal system by my late colleague Warren Loomis. Warren also pioneered the forward face rowing system:
http://forwardface.com/

Hope these are a few ideas to get you going.

Rick W

 

Here is the twin foil configuration. This set up has steering and reverse because the foils are fixed to the vertical strut. This means their angle of attack is controlled. They work like a fixed pitch prop which is not unusual. Initial load is high but once moving they move freely. If you stop cranking they try to drive the foil to a full up or full down position.

There is still some engineering involved to get it to work nicely and it is not as nice as a wide torsion controlled foil but it will definitely work well. You need to consider the forces involved and balancing might be needed depending on the weight of the foil. A bit of ply with some shaping works fine for the foil. As before the side wheels are only to show the crank path. It could just be a simple crank arm. The angular location of the crank handles is important in relation to the forces. You want maximum leverage when the the foils are mid stroke.

If you stroke the foils out of sequence they will tend to rock the boat. This might create more back movement then you would like.

It would be good to have access to someone with shop ability to make this. It would be quite nice if engineered properly. They may be able to find a market for it.

I can do all the math for the system but it is easy to do it by trial and error. I would start with foils as drawn 2ft by 4" moving plus/minus 250mm.

Submerged foils will work mush better than foils that break the surface because the do not ventilate so you get both sides of the foil working.

There is infinite variation with this type of oscillating foil arrangement. I am not sure if I have contrived the simplest solution for you.

Rick W.

 

Rick,
Thanks for the input. More stuff for my brain to chew on (mm-m, chewy!).

If I go with a foil, it will be full-width, one piece, for simplicity and lightness. I hadn't even thought very much about using two, and it sounds even less appealing after you said

Don't want that!

See the attached, it's the first notion I came up with, and isn't fully developed yet, but you get the idea. I'd want it to project off the back of the boat, so it could be swung up for beaching and for loading it into the truck.

I haven't done as well as I should in stating all my needs yet. The places I usually use this boat are quite shallow in spots, and sometimes have big weeds in the water, so whatever I settle on should have as shallow a draft as practicable. Ideally, the thing would kick up by itself upon hitting an obstruction, but that's pretty unlikley; a manual kick-up lever would be okay, but I might just be able to design it with a quick release pin or some such, so that the whole assembly can be swung up as needed.

Which brings up the question, why so much excursion for the foil? I wouldn't think it would need much more than about six inches (15 cm). I base this on an estimate I made after watching this video:

http://www.instructables.com/id/How-to-Fly-a-Human-Powered-Hydrofoil---the-Aqua/

The foot platform is about two feet above the foil, and you can see that the depth varies by maybe a fourth of that. Also, in the papers by Jones, cited earlier, the linear excursions of most of their test models seemed quite small. I may have misjudged that, of course, and their power-extracting device did seem to have a deep stroke.

That would be me. I have a workshop, with a drill press and some other tools. The necessary skills and equipment shouldn't be much more than what it took for me to make the stabilizer.

That's about all I can think of right now. Hope the weather isn't being too harsh for you down there.
peace,
Curtis

 

Rick,
You know, something just occurred to me about the foil drive -- if I have it off the back, as shown, then it's gonna pitch the whole boat, huh? Some of that action-reaction stuff . . . could be a pretty annoying effect on a boat this size and weight.

I guess that would explain why yours is shown on the midline . . .

Gotta chew this idea a bit more before I swallow it.

 

Curtis
Yes the pitching is why you want it under the CoG or close to it. That said the boat has quite buoyant ends so it may not be that bad.

The foil on the aqua skipper is a monster. It is about 8ft wide and 6" long. The drag on the whole thing is also very low and rate of bouncing is quite high. All this works toward having a small sweep range.

The twin foil system I drew could be set up with the cranks 180 degrees out of phase on the foils so your arms work out of phase while the foils are in phase. This should reduce the risk of rocking. These could be made to just drop over the gunwale of the boat and clamp down so not much different to oars. You may be able to get away with about 300mm sweep. They would certainly be worthwhile testing out. You can work in shallow water by only doing a partial rotation. The speed of stroke needs to be faster in the direction you want to travel - reverse or forward.

For shallow water operation in calm conditions it is hard to beat paddle wheels. Something like 12 blades off a spider. The blades would be say 12" wide by 4" deep on each wheel. Use the same sort of crank drive I have shown for the foils.

Rick W.

 

Rick,

I'm wondering now, if having two foils in countermotion would work -- one goes up while the other goes down. I don't see why not. Let me know what you think of that. It could be pretty easy to implement, a simple rocker.

I'm surprised to hear that; I'd have thought them pretty ineffective, but maybe not. One more approach to consider; thanks.
Curtis

 

The rotating wings that the Hobie Mirage uses is probably the best design to avoid unintended consequences from the forces. These develop maximum thrust as they sweep through the 90 degree point so create opposing lateral forces.

It is not too hard to get paddlewheels up in the 70% efficiency range. This is better than paddles for "untrained" rowers. For the little dinghy there is probably little point in having better than 50% efficiency unless you want to paddle for long periods. I have not done numbers but I suspect 40W would see it starting to make waves. It is an up hill battle from there. Very little gain for extra effort. Attached photos shows the university teams in 2004 waterbikes. You can see by the boat planing that they are doing a fair speed. The two paddlewheelers are up with the rest. I think paddllewheelers have actually won the overall event on occasions.

Rick

 

Let's go back to the single pitching foil case of posts #10 & 11 again. It's the simplest case of this family of drive, and I'm a big fan of simplicity.

Further thought on this leads me to believe that the induced pitching of the boat would only become a problem at some range of critical frequencies, and could be cured by mechanical damping. Probably one of the easiest approaches would be to set up the linkage such that the induced pitch is countered by my own body movements as I shift my weight back and forth when pushing/pulling the actuator. Since one stroke of my arms = one stroke of the foil, that approach works at all frequencies.

Adding a second, stationary foil would also serve to dampen vertical motion of the boat, especially if the stationary foil was wider than the moving foil. I can't be sure, but I think it might also straighten the flow a little downstream. Is that right? If it does, then that might help as well.

The real enemy here is the length and weight of the boat, in spite of it having bouyant ends, as you mention. I'm guessing at a waterline length of about 82", and it only weighs 50 lbs empty, say about 225 or so loaded, so a little induced motion goes a long way. That's the problem with retrofitting anything as opposed to designing it all from scratch.

Let me know what you think. Thanks.
Curtis