Pedal Powered Boats

John,

That depends. I would consider epoxying two or three veneers (on braces, so curved) together and then a couple of 16 oz cloth layers on top (exterior). That may even be over-kill, because you're running a cat there will be no point loading in your hulls. Any chance you could get a couple of used rowing shells cheap?

-Tom

 

Rick indicated in a post (somewhere on the archives of this list) that an electrician's drill shaft (I assume 1/4") was used at one point in Greg K. record breaking 24 hour boat. This was an endurance record, so probably no problems with low shock load due low, steady cadence....
http://en.wikipedia.org/wiki/Greg_Kolodziejzyk
This was because nothing else could be found in Canada in the larger diameters on quick notice. The flex shaft was run without a strut in that boat to get better efficiency... I think the 1/4" electrician's extension will work for what you have in mind especially it won't have much of a curve in it, unless you will be sprinting a lot. You can reduce the curve by using a stiff upper section of aluminum tube and shorter section of flex or even control the curve with skeg position to a degree. Besides, even if it breaks, you only lose a short section of shaft and cheap prop. You can carry a spare of each on board that quickly slips in for replacement. I use a quick release hex connector in my setup and this is replaced in a few seconds. Losing a homemade prop would be different as this would be a great loss of many hours of delicate, time consuming labor.

As regards your post above on converting a bike to a pedal boat, the prop in your attached picture from Rick is not a model air prop, but one of Rick's homemade ones, from what I can make out... Yes, the 2 look amazingly alike in general shape...

Unless you are racing or trying to set records of some sorts, I don't think a custom made prop is necessary regardless of configuration. At least one successful commercial version of a human pedal unit by Bob Stuart used the APC 16X16..

The flex can be configured to come straight out of the gear box and into the water as pictured in Ricks post, and is even easier to do with a cat.

P.

 

Hulls

John
The hull I made has the shaft going through it. This was to suit the gearbox I have, the shaft comes directly from the gearbox to the prop. It is a very simple setup, gearbox - shaft - prop. The less parts and bits the better, Ricks V14 uses a bike chain driving a 1:1 gearbox with the shaft running down the side of the boat. Your setup will be dictated by your drive/gearbox setup, the 1:8 ratio with correctly sized prop will have no problem pushing the boat. Get a strong sturdy gearbox as with a small one you can strip the gears ( I'm speaking from experience). The key is the right prop size, too small and you will spin like crazy and get nowhere. Too big and its like trying to ride up hill in top gear.
My boat has a solid section of 16mm aluminium rod 2m long that runs through the hull and is fixed to a 8mm spring steel flexible shaft 1.3m long.
You can use plain steel rod or 10mm aluminium rod for the flexible shaft as long as the curve is shallow (6m - 7m radius). The cat layout will make it easier to setup your drive and seat. It makes raising the flex shaft out of the water easier and also if want to steer using the flex shaft.
With your boat size try and make it as long as you can. The constraint will be transport/storage. How will you get it to the water? With my boat I transport it on the car roofracks, and then assemble it next to the water.
I have since learned that a shaft on an angle puts a large load on the prop and gets a lot of vibration plus loss in efficiency. The flex shaft allows the prop to spin vertically at its most efficient.
I did a quick rough calc. and two hulls 4m long with a beam of 250mm would draw about 100mm of water. How much freeboard would be determined by where you are using the boat.

Ian

 

Drive system

Zipboater
Your props would have a terrific speed, 1:27.5 ratio. Thats about 1900rpm for a 70rpm cadence. Could you post a pic on this forum, would be great to have a look at it. These things always take longer than you think, my rule of thumb is estimate a time and then multiply by 4. Good luck.

Ian

 

Thanks to all for your input.

Attached link (http://www.mitrpak.com/product_datasheet.php?product_id=31) is what Rick had posted in one of the earlier threads. So I understand that on one side of the gear box I would need to attach a sprocket to the shaft in order to attach the chain coming from the bike crank (I assume this is done by wedling the sprocket to the shaft ???). Can someone describe (pictures helpfull) of how you would connect the other shaft of the gear box to the shaft holding the prop (be it flex or solid)? Then, how does the prop get attached to the shaft?

Ian; as for the size of the hulls. I don't have a transport problem as I live on the water so if bigger is better (more stable/faster) then bigger they will be. Can you recommend an "ideal" size (legnth/width/hieght of the hulls and the spread in between) for my application (inland bays/canals: 225lb passenger load: water depth not an issue). Again, my off the cuff thought for the hulls was 12' long by 1' wide by 1.5' high seperated by 4' in between. Am I way off here?

Thanks Again
John

 

Project Torpedalo

Hi all,

Just came across this excellent forum, and thought you might be interested in a project I'm running together with my friend Mark. We've designed, and are about to have built, a trans-Atlantic pedal-boat, which at the end of this year we're going to attempt to pedal across the Atlantic Ocean to raise £250,000 for two charities and hopefully set a new World Record. You can check it out on our website at www.torpedalo.com, and follow us on Twitter (www.twitter.com/torpedalo) and Facebook (www.facebook.com/torpedalo). I'd be delighted to answer any question you have about the design, construction and operation of the boat or drivetrain.

Thanks, all the best

Mike

 

Torpedalo

You guys have your work cut out, 248 days to build the boat. Then fit it out and test it. Good luck!

Ian

 

You're not wrong. The whole build is being done for £0, through two main sponsors. As they're working for free, we can't demand priority over paying customers. Nevertheless, a timing plan is in place which will see the boat in the water by the end of July. Only gives us two months for testing, as opposed to the originally planned five, but if it was easy it wouldn't be as fun!

 

Catamaran

John
On my first boat I used a bike crank with a chain turning the gearbox. The sprocket I got from the bike shop was a problem fitting to the gearbox. I modified a few washers and bolted it on. Fixing the shaft depends on the gearbox, you could file a flat piece on the gearbox shaft and use a grub screw. I use a piece of tube between the gearbox and drill a hole at each end for a bolt. With the propeller I have been using a square rod fixed to the end of the shaft. The prop is made around a square tube, a piece of wire through the end of the square rod stops the prop from falling off. Another way is filing a flat piece on the shaft and fix the prop with a grub screw through the prop hub.
The size of hull you have shown will work but go up to 6m (18ft-19ft).
Over this length it can get hard to manouver, gives you that extra carrying capacity if you decide to do any extended trips and have to carry food etc.
Have a look at the Open waterbike website, lots of info there.
http://www.openwaterbike.com/

Ian

 

Ian

Thanks for the info above. I started doing some hunting for supplies and I came accross some right angle gear boxes that had ratings of 5:1 all the way up to 60:1. Now these were referred to as speed reducers, meaning they were designed to have you connect some type of motor to the input side (higher number) and the output side shaft speed gets reduced down to 1, right? So can you use this in reverse, meaning connect the chain from the bike crank to the shaft on the 1 side and have the output side the larger side (higher rpm) going to your prop? Is this doing something different than the Mitrpak 2:1 described by Rick? Will the RPM's be too high for the prop? Will the crank be impossible to turn? Would this not give you additional speed?

See attached link and let me know what you think.
http://www.surpluscenter.com/sort.asp?catname=powerTrans&keyword=PGRSescribed

Thanks
John

 

Gears

John
Had a look at the website, looks like they may be worm gears from the way the shafts were positioned. If they are worm gears they won't work in reverse, its that type of gear. The mitrepak gears are spiral or bevel gears and are designed to work both ways. Better to spend a little extra on a robust gearbox that will do the job.

Ian

 

Ian

Yes, you were correct, they were worm gears. I did not know the difference. Can't say that I was not trying to save a little $$ when I stumbled accross them (who doesn't like a deal), but the other reason that they caught my attention was the higher ratio's offered (just figured if 2:1 is good, 10:1 must be better) would yield higher RPM's at the prop. So I guess I will take your advice and go with the Mitrpak. Just one question, the setup you have, pedal crank directly into gear box, is that your own creation/fabrication or is it available commercially anywhere on the internet. I guess eliminating the chain is a plus (KISS) but do you loose any prop speed, are you still able to achieve 8:1 ratio (as Rick described) from pedal to prop?

Thanks
John

 

John
The gear ratio of 8:1 is not the only one you can use. Any ratio will work as long as the prop is correctly sized. A 2:1 gearbox directly connected to the prop will work but you will need a prop size of about 500mm dia. The slower the speed and larger the prop the more strain is placed on the gearbox. If you can get hold of a 4:1 gearbox it would be all you need, no chains. I use a 3:1 gearbox with a 430mm dia prop, the cranks are fitted to the gearbox. It was made by Involute but I don't know if they are still available, it is heavy but very strong and will last. The cost of a good heavy duty gearbox is about the same as a cheap mountain bike.

Ian

 

Ian

Can you explain the calculation to me for the relationship between gear ratio and prop size? So in your previous post you say if you are using 2:1 (say at a 60 cadence) generating 120 RPM at prop you can use a 500mm dia prop. Or if you are getting 3:1 (again lets say at a 60 cadence) generating 180 rpm at the prop you could use a 430mm dia prop. I assume with all other things being equal (boat size/weight/length and rider) the resulting speed would be the same???

In addition to explaining the calculation can you explain at what point the legs can't take it? So for example in the above, if you are getting 3:1 as in your case, is there no benefit (increased speed) by having a larger prop (500mm) and/or is it the resistance is too much for the legs?

So in the end I want to know what will give the most effecient outcome for speed and comfort to the rider. You recommend above if I can find a 4:1 gearbox I would not need any chains. But I have been unable to find anything greater than a 2:1 (Mitrpak) that is not a Worm Gear.

So if I was to use the 2:1 gearbox and some combination of sprockets that could offer between 2:1 up to 4:1, how could I determine the "BEST" prop size for speed and rider compfort?

Thanks
John

 

John
I have a set of instructions for making a prop out of a piece of steel flat bar, approx. 30mm wide x 3mm thick. If you can make your own prop I can give you the size and angles. First step is to go ahead and make your drive unit, a mitrepak gearbox at 2:1 ratio and a bike crank and pedals. Make it as one unit with the gearbox as close to the crank as you can get it, this will keep the chain length to a minimum. When it is made you can get the exact gear ratio between the crank and the drive shaft. I can then work out using Java Prop the size of prop required, it is worked out by the cadence and the power. The program works out the width and angles of the prop, you put in the revs and the power. If you have a cadence of 60 rpm this equals 480rpm at the shaft for a 8:1 ratio, for a 4:1 ratio the shaft is spinning at 240rpm. The thrust generated by the props of different sizes is the same, a large slow turning one or a small faster turning one. It is the same principle as force by distance, the same amount of work is done. The higher the prop revs means a smaller dia prop, just as lower revs give you a larger prop. I have a chart for power levels for people of varying degrees of fitness and duration. Sizing the prop is like getting the right gear to ride in on a bike, only difference is there are no hills so you only need one gear.
If you buy a prop you have to size the drive to suit which is a bit like putting the cart before the horse. Can make it difficult getting the right gearing.
If you want the prop making instructions I can email them to you.

PS. You could use the Mitrepak gearbox in the same way I have shown on my last post. I could size a prop to suit, you would have to check if bike cranks can be fitted to the gearbox.

Ian