Pedal Powered Boats

Thank you all for your quick replies and warm welcome.

Jeremy, I will definitely try and take your advice in terms of some simple tests, there seems to be a definite disadvantage when you start twisting chains since none of the manufacturers data expects you to! And thank you for the Technobots recommendation.

We had a meeting today with a man who might be able to supply us with a canoe hull for a very good price, which would be well suited to having pontoons fitted, meaning the cat design may well take a backseat.

We're setting our aims high and hoping to get up to world record speed over a 100m flying start sprint (the decavitator and youtube have been very useful sources so far). We'll hopefully be able to persuade a few members of the university cycle team to act as our engines but will also be designing so that we (reasonably fit 20/21 years olds) can get it up onto the foils. Expectations may well have to be adjusted along the way, it's going to be a steep learning curve!

I've had a look at the SpinFin, it definitely gives me hope that a twisted chain could work, and I hope we can come up with a name as fantastic as the Lambordinghy!

I know it has been mentioned in another thread but does anyone have any experience in using a belt drive? I've come across them used in HPBs, but only at low speeds and loads.

The main reason I was initially swayed toward a twisted chain was the bulky and heavy housing that seems to be necessary in order to keep beveled gears properly aligned. I've come across one university project that built their own carbon fiber housing around their gears:
https://netfiles.uiuc.edu/ro/www/CetanHumanPoweredHydrofoilProject/cetan2_5.html

Has anyone tried this themselves or have any thoughts on our likelihood of success if we tried this (considering we are 4 students with absolutely no experience with carbon fiber)?

Again, any thoughts and advice is extremely appreciated,

Emily

 

Hpsb,

If you want to do anywhere close to a world record time you need something narrower than a canoe. I suppose the entire timed sprint will be up on foils, but you need to get up to speed and a canoe is typically heavy.

Read up on this thread, pay particular attention to "Rick"

Good luck,

Marc

 

I agree with Marc, you want a hull that's longer than a canoe, and lighter. Rick Willoughby undertook a number of careful experiments, developing better and faster boats with each iteration. He left this forum (a significant loss to us all) but his posts remain in this thread under the name "Guest625101138". Pretty much all he says should be read carefully, as he was methodical in his approach to getting the most from pedal power. He has a web site with some photos of his boats, here: http://www.rickwill.bigpondhosting.com/

Rick made several hulls simply using flat sheets of foam cored composite sheet, laid up on a flat surface, then cut and bonded together. This is a simple way to make a light and stiff hull.

 

Emily:

Since you are going for a world record and will be flying at the start with a water prop, I would think the approach will have to be adjusted. Power (trained cyclists) to weight (carbon fiber structure) ratio as well as air (Gossamer albatross) and water (minimum drag water projections -strutless props?) streamlining would come into play to a very large degree. Probably need 2 machines or a design that allows for quickly interchangable parts including fitting different pedallers. Most machines designed for a single purpose like this are as fragile as possible to save weight and durability considerations can be downgraded. The twisted chain with air prop has been proven in the decavitator as well as pedal plane records, so probably no advantage to a gearbox. Keeping down the cost may prove a challenge because of special materials with high strength to weight ratio. A small lightweight sculling hull might work better than an canoe.

Porta

 

Hi Coach Dave,

I have seen photos and vids of your craft and it still amazes me that you don't have an engine hidden somewhere in there! It has changed my long term view of the sort of boats I might be able to use around here. (Nova Scotia). For now though I will stick with my plan and get a boat to play with. I have about half of one hull of my catamaran built to date and it seems to be going well. I am starting a blog and once I get a couple photos on I will supply a link. It's my first boat so there are a few small wrinkles.....but nothing serious. This won't be a feather wight but will make a great testing platform!
Now that you are using a carbon wrapped prop shaft, what do you think your minimum water depth is? I am a bit concerned about having the shaft unsupported in shallower areas since I assume that when you stop pedaling the shaft wants to straighten out. There is lots of deep water around here but it just means I will have to stay further from shore. I will be almost always in salt water so I am worried about corrosion as well. The gear and twisted chain units are attractive but I really like the idea of a shaft going over the side that I don't need to keep sealed!
1/4 stainless steel shaft sounds a little light from what I read here and I have a listing for 9/32 (303, not the best alloy) which might be better. I have lots of room on the cat so I can move components around and try to maximize the bend radius.
Glen

 

Hi, Glen.
Regarding minimum depth see post #54 on a clip I sent to Rick some years ago: http://www.boatdesign.net/forums/inboards/prop-shaft-systems-24636-4.html

Unless there is something to tangle up the prop, like seaweed, there is essentially no limitation on the shallowness with a flex shaft because of its ability to bend.

Porta

 

Thanks Porta,
The idea of the prop thrashing along the bottom is certainly counter to the usual way of thinking about protecting the drive line! Is there a linear relationship between prop efficiency and angle to the flow? Is it as simple as a force vector diagram where you can separate the loads into horizontal and vertical components? Some commercial boats seem to have tried to get the shaft as horizontal as possible while still keeping the rest of the driveline inside the hull and just accept the losses.
Thanks, Glen

 

An image and a video of Rick's from earlier in the thread, illustrating the flexible shaft:



http://www.boatdesign.net/forums/at...495-pedal-powered-boats-v7_strutless_prop.wmv

The video shows quite clearly, how, as the boat turns, the prop moves from side to side to align with the flow.

From Rick's original post, #161 in this thread:

 

Glen:

The inefficient aluminum prop in the film clip was from a Thai long tail which is meant to sweep the bottom like many mud motors. This would probably not work as well with one of Rick's efficient props, except maybe the folders.

I don't believe the relationship is linear between prop efficiency and angle of flow. An angled prop probably doesn't lose as much as one would think, unless it is at a very severe angle. At least the angle didn't make much difference in Greg K.'s 24 hour hpb record set with the flex shaft, about 2% compared to comparable shaft with an efficient support skeg, according to Rick. But you don't have to worry about angle with a flex shaft, as the angle always remains at the optimum.

P.

 

Hi Glen,

No I don't have a hidden motor, just me pedaling. A motor would be faster but I enjoy the quiet ride. I usually have 2 to 8 other people in the boat with me and can go in the no-motor zones like a manatee santuary that is nearby. I am using a 20" diameter prop and need to keep it about 4" below the water surface to prevent it from ventilating and slipping. That makes my minimum water depth 24" although 30" or 36" gives some operating margin. If the prop occasionly hits a rock or branch it isn't a problem because the driveshaft will flex allowing the prop to move out of the way. If I see the obstacle soon enough I pick up the driveshaft to avoid striking it with the prop.

Yes, 1/4" stainless steel is too flimsy for my heavy boat. It was my starting point, served me well, and I can still take it along as a backup. The carbon fiber shaft is a big improvement and should hold up well to being immersed in salt water. I've started working on a smaller boat to be used for 1 or 2 people. It will be running at a higher gear ratio (faster shaft RPM) so it should work OK with a 5/16" stainless steel shaft. The 1/16" difference between a 1/4" shaft and a 5/16" shaft might not sound like much but it results in a shaft that has 2.44 times the torsional stiffness. I like not having any gears or seals below the water surface since those gave me problems with earlier prototypes.

Good luck with your catamaran construction.

Dave

 

Forward Outriggers

Modified my boat yet again, this time have moved the outriggers to the front of the boat in an effort to reduce the drag and improve trim. On the lake last Saturday and noticed how much the bow rises the faster I go, at least 50mm in a sprint. What happens is the outriggers which were skimming the water are sinking deeper the faster I go. Have now mounted them at the bow, the weight trims the boat slightly forward but what now happens is they stay above the water the faster I go. Tested it out at the rowing course today, boat feels a bit less stable and tends to flop one side to the other, might have to lower the outriggers slightly. Didn’t take the camera so no pics yet. See how it performs the next few times out to see whether I stay with the layout or go back to the way it was.

Ian

 

Interesting.

This is opposite to Rick's design.

-Tom

 

It would be interesting to hear how your boat performs with wind/waves coming from 45 degrees off the bow and when it comes from 45 degrees off the stern.

Michael Lampi

 

Forward Outriggers

Had the boat at the lake on the weekend, conditions were calm with only small waves. I lowered the outriggers a bit to try and minimise the flopping from side, still does it but not as much. As much as I tried I could never achieve both outriggers out of the water, even a slight lean one way or the other was too much. Having the outriggers forward allowed me to see a lot better how much they were digging in and I could correct it before it dug in too far. The stability is just as good as with the outriggers further back, being able to better keep it on an even keel has to reduce drag and improve speed. Stick with it for now and see how it handles in rougher conditions.

Ian

 

Would SWATH outriggers be feasible?

-Tom