Pedal Boat Design

Ah, I get the 60 degrees now. Thanks.

Crank rods...like on a locomotive? Or are we talking gear boxes?

If your thinking like a locomotive, that may be more efficient or faster but it is also a lot less user friendly. I see a lot of banged shins.

I went with a split wheel because every rider is different. If one pedals faster then the other or needs to take a brake or ease off for a while the other isn't then carrying "dead legs".

All boats are compromises to different design goals. Some are all about high performance where the metric is raw speed. Most try to balance several goals. Mine are good performance, stability, shallow draw, ease of use, safety, durability and enjoyment. With a healthy dose of sex appeal or "beauty lines" tossed in for good measure.

Having the wife beat my shins black and blue pretty much misses all of those lol. We don't have to cover a lot of distance in a short time. Nobody else has boats we need to race. Your pretty lucky to live in a place where there are other enthusiasts and you can use a prop.

When we move to the Oregon coast...

 

Curtis-

Attached find 8 images that should help--if theres another view you need just let me know.

You asked earlier why I went to 7 paddles in place of 6...these should answer that lol. I might even go to 8 or more if it were me.

 

Yes like a loco.

I see rods much more user friendly than chains. Touch a chain and you have messy oil all over you. You could just set up levers without cranks but requires some thinking about.

The last thing you want is to be dragging a fixed paddlewheel through the water. Even a free wheeling one will be bad enough. There is the added drag that has to be overcome by the working wheel and the boat will be in a permanent turn.

So if one rider does not want to work then they must have a foot rest. Cannot stop turning a wheel.

There is also significant advantage in having phased pedals. Boats are different to road cycling. You do not have the momentum connected as directly as a bike on a road. It is akin to cycling in sand. Carry-through the dead spot is a big issue. It is a real advantage for two riders even if one is not working very hard the extra carry-through for the working rider is a significant benefit.

 

Thanks, BG. I'll have to stare at those for a while, and I guess I need to start constructing a model, maybe more than one. I think I know why you like more blades; looks like having more in the water might smooth out the action. I know there's got to be some law of diminishing returns involved there, but I couldn't guess how to figure it out.

I was getting pretty discouraged and aggravated about this thing earlier today. One thing that worries me a little is that the outboard end of the shaft being only about two inches above waterline, little waves would wash over it and slow it down. I don't know. It doesn't look bad in your pictures. I'll just have to experiment, I guess.

I'm working up a construction method for the models, having a tricky time with the mounting. I'll get it. It'll give me something to do.

Curtis

 

Food for thought for sure.

I think if I break it down though it still comes out on the plus side for a chain (for me at least).

Greasy spot versus clobbered shins. I'm going greasy spot every time lol.

As for dragging the wheel. I wouldn't mind a free wheel though I don't know how important reverse would be on a paddle boat. As for braking with the wheel...pretty easy to rig brakes for it just like a bikes.

And by differing rider power output I agree a rider taking their feet off the wheel frees up the dead leg load on the other rider, but I meant the much more common case where one rider pedals at a different rate/energy then the other.

As for one wheel dragging and turning the boat, with both wheels on the centerline as opposed out on each side of the boat, I think it will be insignificant. If there WAS the tendency for it to turn the boat that would be pretty handy for maneuvering. Much like reversing oars.

Just seems the more 'elegant" solution for our proposed use/environment. I admit I had not considered the loco arms though and it is interesting. For a single I think it might be the way to go even.

 

Curtis--

Yup, even with 7 theres a point in the rotation where only 2 are wet.

My really big concern though is having one end free floating. Originally you mentioned wanting to cut the wind area down some. I am not positive the angled wheel really does that.

I did a neat one with 2 wheels center mounted where they meshed together like a blender...pretty neat lol.

As for building models...that actually sounds like fun =)

 

Ah, but such is not the case if the paddles are feathered, and enter and exit the water perpendicular to its surface.

Check www.bikepartsusa.com . I bought from them years ago and found them to have a great selection and pretty decent prices.

 

Tinhorn--

Rick actually says "immersion for unfeathered blades". I suggest blaming it on the Gin and Tonic =)

Rick--

On a 36" (.91m) wheel that works out to a tad over 2" of paddle depth. Call it 2.25" or about 6 cm. Do you really mean THAT shallow for the blades? Keep in mind that is with the inner most edge right at the water line. I would guess that means running the blades say 3-4 inches but with only about 2 to 2.5" submerged. I guess adding more blades. Let me look at 16.

 

BG,

No, no way the outboard end can be unsupported with that much torque. I'd have to come up with some sort of framework to support the outer end of the shaft.

The trick of this is, that in order to get this into my pickup, I'll have to be able to remove the wheel assemblies and their support frames. I don't think the frames need to be very complex, but they have to detach -- some kind of clamp onto the gunwale.

As for windage, that's the greatest appeal of this conical design; it gets much of the wheel down lower. If I thought that the 90 degree wheel could be useable, it would be level with the top of the gunwale -- no extra windage at all.

How do you mean? Was that a stern drive? I'd be interested in seeing it.
Curtis

 

In the Excel file I sent you the working depth of the blade is given. And yes it is not very deep for a small diameter wheel. 12 blades, as I recommend, is consistent with the 60 degrees of immersion as blades are spaced at 30 degrees so never less than one full blade working at any time. The immersed blade area will be close to constant. I would not make the blades much deeper than their intended immersion. It will add windage and lift more water when in waves.

In terms of a single wheel I was contemplating side-by-side seating rather than in line. I think you would find the roll less inconvenient than the pitch. You can always partially offset your weight with cargo in the opposite hull. You have less bending moment in the bridging structure. It provides a friendlier seating arrangement. Only disadvantage is a very slight increase in windage. If I am interfering with your fettish to see a soft bum churning away in front of you then please tell me to mind my own business on this aspect. My main objective is to see you use the full space for the width of the wheel.

I think you will find lever arm pedals more natural than cranks and these would work well with the rod and crank arms on the wheel. Using a recumbent position without clips is quite tiring for long duration. It would bear close examination in comparison with a chain. That said my positioning is very recumbent. Back angle is about 30 degrees. I literally lay down on the job. I have found myself heading for a shore at 10kph while snoozing on the job just rolling my legs over.

 

It would have reduced effectiveness. There are drag coefficients provided in the table down this web page:
http://www.aerospaceweb.org/question/aerodynamics/q0231.shtml
The value I have in my model is 1.1. This is for a square plate. A long thin plate is quite a lot better. I do not make any adjustment for this so efficiency for long narrow blades will be better than the Excel sheet provides. BG could go to maybe 1.7 with a full width wheel.

Going to cylindrical paddles the Cd will be more than a sphere (0.4) but less than a long cylinder (1.2). By comparison the flat plate will be more than 1.1 but less than 2.

Cupped shapes give the highest drag but they lift water. There may be ways to drain them without losing effectiveness.

Rick W.

 

Thanks, Rick. That's a good enough reference for me to print and put in the notebook.

Curtis

 

Rick--

Sadly the the chubby bum in the front seat would be me =) as I outweigh the wife by 100 pounds. My thinking was that her weight plus the wheels, which is further away from the center line, might help with fore / aft balance.

I really considered a side by side arrangement early on but either designing the seats to move left/right on the center line or using cargo to balance out passenger weight difference seems...lazy to me some how. I have several fishing buddies that have widely ranging weights also.

I went ahead and made a chart showing the degrees for three different blade depths based on the water line at those lengths just to be sure I am getting your 60 degrees correctly. It would seem that for a 36" diameter wheel the paddle is going to be right in at about 2.5" of height...or depth lol.

I hit the first real downside of the paddle wheel versus prop last night. My first wheel design was 32 pounds (12.5 kilos). I didn't even feel like it was an excessive structure either. I would love to get the wheels down to 10 lbs each or 20 total. We shall see. 12 blades is a start.

My real concern with not having the extra blade height is missing on the weight estimate and having the wheel riding too high. I may make it so the wheels height is adjustable. Not variable while in motion per say, but easily enough in the shop.

 

BG,
32 pounds??!! What'd you do, copy one of Tinhorn's cast-iron and oak-plank jobs? There are whole bicycles that weigh less than that -- quite a few of them, actually. Wow.
Maybe bicycle wheel construction is something you could look at for reducing the weight on those. Too bad they don't come in that kind of diameter, you could just grab a couple and string the floats across 'em.

 

I do the depth analysis in the spread sheet for 60 degrees. Your numbers certainly look close.

I would definitely allow some ability to trim the height setting of the wheel shaft. I would also like the ability to trim the blade angle. You could build a test wheel that has the adjustment then make lighter fixed wheels. The lightest/strongest construction is carbon fibre over honeycomb like Nomex. You can make up a flat panel and cut up for blades. It is not difficult to make flat panels that look good.

The very simple hard chine hull I sent you will stiffen up quickly. It will require a lot of weight to set it deeper once it is partially loaded. I suggest you look at the roll created by having offset weight. You need to work out the load on each hull. I can give you the draft of the hulls for various loads. Do you have a beam restriction? I doubt that you need any provision to move seats if they were set up side-by-side