Pedal Powered Boats

[beppe]

Originally Posted by I57

Does anyone know the best position for the seat in relation to the pedals. Is there an optimum angle for the seat backrest, I have mine so that I can adjust it but am wondering if I am leaning too far back. With the seat height in relation to the axis of the pedal crank how low or high should this be. The open waterbike shows the bottom of the seat at the same level as the crank axis but a lot of boats have the seat much lower.

Ian Cassell

Hi Ian
In our cat that won the World Championship (long distance regatta, singles) back in 1999 we set the seat height 50 mm (2") over the crank axis level, according with Jake Free's advice for sustained (several hours) efforts.
Since then we were satisfied with this arrangement, so I proposed 0 to 100 mm as an optimal standard. I know many pedal powered boats have the seat level lower than the crank axis (as most of the recumbent bicycles, including mine) but i believe it is a trade-off between biker comfort and other issues (like the position of the center of gravity of the craft); if the genertal architecture allows for that, I'd follow Jake Free's advice: seat at the same level of the crank axis or higher. But I look forward to other experiences...
I remember that correct angles for the seat are discussed in 'Huma Powered Vehicles", the book by Allen at al, but I haven't it here (I'm in holiday ;-) so I can't verify. I believe it should be adjustable in a wide range.
Beppe

[alexlebrit]

Rick thanks for that, after a few scetches it all made sense.

I'd wondered about fixing the "drive cables" to the hull aft of the swing arm and not the swing arm as in your design, and then looping them forward over pulleys fitted to the swing arms and then back to the drive.

This would mean for every swing-stroke you'd pull twice as much "drive cable". Yes, the effort needed would be greater, but I wondered if the potential increase in prop speed, possible decrease in prop size and/or possible reduction in swing arm length would more than make up for this.

Also can I find roller clutches anywhere in deepest darkest Brittany? Nope (mind you I don't know what one is in French) so I'm considering using single speed bike freewheels in their place and running bike chain over them. In my mind I could see that a single piece of chain could be looped round one, then over a jockey-wheel and then looped over the second. Yes
there'd be slight twist in the chain, but not a great deal and I think it'd handle it. Then this would be attached to the "drive cable" using cable eyes to attach to the chain link pin as in the existing system. And of course it means no slip and no reeving - hoorah.

Now, I await the potential problems.

Alex

PS. Also posted this on the hpv boats mailing list, just in case you're thinking, I'm a mad-multi-poster.

[Guest625101138]

Both Warren and I got the prop rpm we wanted with single ratio of the pulleys. His prop is 300mm
and mine was a bit over 400mm. Going to a smaller higher speed prop would almost certainly educe efficiency.

The chain sprocket will work and there is/was a swing arm bike available using freewheeling sprockets. The feature of the roller clutches is that the backlash is negligible. They do not rely on pawls but just friction on a hard shaft.

Timken manufactured the ones I have:
http://www.timken.com/en-us/products...CupRoller.aspx

Rick

[alexlebrit]

Whilst effeciency is always good, I do like the idea of a slightly smaller prop, it's just less dangling under the boat potentially getting damaged. But, it's not the most important thing in the world.

What I was thinking though is that doubling the cable pull for each "swing" would also mean I could halve the crank length, I've never been keen on the feeling of a top pivot crank, I don't know why but my feet don't seem to like it. You've mentioned previously that you have a 400mm crank with the pedals at 300mm, which is a bit long to have bottom mounted unless the seat is mounted high. If I can double the cable pull for each stroke then I could for instance have ordinary bike cranks, in fact it would even be possible to have a complete bicycle crankset witht he pulleys mounted outboard on the pedals, and consequently have a full rotary motion at the crank.

[Guest625101138]

Alex
I did the mechanical analysis of the geometry I ended up with. One of the benefits with the top mounted pivot is that the feet lift toward at the end of the stroke so there is some natural harmonic motion through gravity going on. If you set the bottom pivot low then you have to rely on solely muscle fibre to provide the restoring force. My personal view on this is that it will cause a cramping of the legs into the gut.

I have talked to one Hobie mirage owner about this and he has noticed it and was actually thinking of biasing the pedals forward with a spring to improve the action. I do not know if he tried it.

I did no-load comparisons with my swing arm system and it was more biomechanically efficient than a simple crank. It is a very nice motion.

All that said, other things are worth trying. The swing arm cycle used very close to conventional cranks with the crank arm operating around horizontal.
http://www.classicrendezvous.com/ima...ax_closeup.JPG

Rick

[RVELL]

FYI, Here are a couple of human powered videos that might be of interest:

http://www.youtube.com/watch?v=sdBSaAZdHio

http://www.youtube.com/watch?v=9iRnSHIrCa0

While on Youtube.com search for IHSIHS for more hydrofoil videos.

Ray Vellinga

[beppe]

Originally Posted by Tiny Turnip

As I am going away on holiday today, I thought I would temporarily leave you with an artist's impression of my boats first trial.
Taken from 'How Tom beat Captain Najork and his hired sportsmen' by Russell Hoban, illustrated by Quentin Blake. As fine a book as you are likely to read.

Adrian thank you for the beautiful image! I knew Quentin Blake's illustrations from Roald Dahl's children books, but I never saw this one of the waterbike - oops of the watersomething...
I wish you great holidays with your pedal powered boat and I look forward to having a feedback about it - I took the liberty of publishing your description of the Seacycle drive unit here:

http://www.openwaterbike.com/archite...le-drive-unit/

and I am very interested of course in knowing how these units perform!

Beppe

[I57]

Finally got the boat on the water today, involute gear box worked great new outriggers performed well. Only problem was the universal joint breaking after 15 minutes, the pin connecting the two halves sheared off. The shaft is set at a 20 deg angle and the UV is 12mm dia, the pin is only 2mm dia so not that surprising. Next step is a bigger stronger UV that can take the load, how much load? Pic of boat is without outriggers, this was when I had paddled back and hauled the boat out of the water. I have the boat about as good as I can get it and now just a case of tuning it.

Ian Cassell

[Guest625101138]

Ian
With 3.3:1 reduction you will find it expensive to get a universal joint that will stand up.

I cannot recall the circumstances that you tried the curved shaft but I think it is a better option with the big box. You need a couple of small bearings in the strut to carry the shaft without damage but you could test first without bearings.

10mm machinable aluminium rod with carry the torque and should not be too rubbery.

The inline torque rating of the universal you have is more than enough but once it has a bit of angle the rating drops off. I do not know by how much. Obviously not satisfactory. Greg had the same problem with this universal. I used one with 7.5:1 gearing and it was fine. Angle was about 12 degrees.

I hope to launch V11J on the weekend. Has been a real pain trying to get epoxy to cure in the cold weather.

Rick

[diwebb]

Hi,
you may want to try www.mcmster.com. This catalog is amazing for all those hard to get items. Prices are a bit on the high side but it is a great resource for right angle gearboxes, flexible drive shafts, universal joints etc and they do mail order to anywhere in the USA, and maybe worldwide? I have not asked that question of them yet.
David.

[alexlebrit]

Rick, I know it's not directly related to the pedalling part, but I seem to remember in the past you've mentioned building in aluminium. I was wondering if you had any tips on this.

[Guest625101138]

Originally Posted by alexlebrit

Rick, I know it's not directly related to the pedalling part, but I seem to remember in the past you've mentioned building in aluminium. I waqs wondering if you had any tips on this.

Alex
I find aluminium sheet the best to use for a fast clean build. There is very little compromise in making developable shape and no finishing required unless you want a pretty colour. Even then a couple of spray cans will do the job.

There are a few things to learn.

I only cut the sheet for hulls using a thin cutting disc on a hand grinder - noisy and messy dust but no stretched edge.

I screw and glue seams to a backing plate for nice shape. Usually stainless screws and polyurethane glue. The glue is intended as a sealer. The boats are never in the water long enough to worry about electrolysis and I store dry.

I fold a tight flange on outside edges of the sheet before folding to avoid kinking the sheet.

It is handy to have some nice steel angle or heavy aluminium tubular section to make nice tight edge bends. Also requires a method of clamping.

You can make usable boats out of 0.6mm aluminium but will be prone to denting. 0.8mm is more robust and still quite easy to work. I class 1mm as heavy duty. A drop will not normally cause any damage but it take more to bend it. The thinnest I can get marine grade is 1mm but I have never used marine grade as my boats are normally used in fresh water lakes and rivers.

If you have more specific question I can give more specific answer.

Rick

[Guest625101138]

I launched V11J today. This is based on the V11 hull shape from Godzilla.

It is a glass on Klegecell hull and I made an aluminium crank frame to save some weight. The boat is 23kg. So a little heavier than planned as usual but very easy to handle.

There were a few teething problems but had a couple of hours of pleasant exercise at the lake. Not fit enough to take on the sailing boats today and the shaft was slipping at the prop if I cranked hard.

My crank mounting is a little too flimsy so I will need to stiffen that up.

The dipping rudders worked very well. These are two rudder blades at a fixed angle of attack that are sprung up out of the water. To turn I just pull a chord that immerses the appropriate blade.

The outriggers fold up for transport similar to V11A.

I have attached some photos including a close up of the rudders.

Rick W.

[beppe]

Originally Posted by Rick Willoughby

I launched V11J today. This is based on the V11 hull shape from Godzilla.

It is a glass on Klegecell hull and I made an aluminium crank frame to save some weight. The boat is 23kg. So a little heavier than planned as usual but very easy to handle.

There were a few teething problems but had a couple of hours of pleasant exercise at the lake. Not fit enough to take on the sailing boats today and the shaft was slipping at the prop if I cranked hard.

My crank mounting is a little too flimsy so I will need to stiffen that up.

The dipping rudders worked very well. These are two rudder blades at a fixed angle of attack that are sprung up out of the water. To turn I just pull a chord that immerses the appropriate blade.

The outriggers fold up for transport similar to V11A.

I have attached some photos including a close up of the rudders.

Rick W.

Hi Rick
your boat looks really fine; I'd have a lot of questions...
Just one for now... why do you need twin rudders? Have you any vibration problems with the chord kick-up system at high speed? We had them. We worked a lot on these problems, before ending up with the solution in the enclosed image & video. We use a push-pull aluminum tube for lifting and pushing down the rudder, and a flexible cable to operate the rudder, so we can have control of it even when it is just halfway, in shallow waters. We also worked on the shape, as yoy can see.
I look forward to more details on the performances of your boat.
Best
Beppe

[Guest625101138]

The rudders are so-called "dipping" rudders. They are only immersed when required for turning. They normally sit up out of the water and are just immersed when turning or course correction is required. For a full turn the whole rudder is immersed. If it is only a course correction then just a tiny portion is immersed. The rudders have a preset angle of attack roughly set at the maximum L/D ratio for the particular foil.

It means I do not have the continuous drag of the rudder. Depending on the size of the rudder it could be worth 0.5kph.

Rick W