Pedal Boat Design

You can just attach an image to the post. See the paper clip icon above the reply window.

 

Rick--

Image attached.

 

BG
That is the one. As far as ease of pushing a hull through the water that is the best you can get for 250kg with 250W at about 75% efficiency. Boats are really that simple.

It is only the underwater bit that counts. You can do what you like above. With any hull I like reserve buoyancy of at least 100%. So with this in mind you can fiddle as you please.

A bit of rocker, bow extensions and flared sides will not alter things much.

 

It seems like my "eyeballing it" was reasonably close. My widest point was a bit forward of yours--I outweigh my wife by a good hundred pounds ...about 75 if you count the aft paddle wheel and its attendant structure. I had also read that displacement hulls do better with their widest aspect at about the 1/3 rd mark so it seemed to work out.

Were you able to open the aluminum down strut assembly and have a look? After having watched the transformations all your designs have taken I have to agree that the first boat should have a simplified structure while you work out the kinks, so a simple welded aluminum structure is easier and faster then the more involved CF job. Best to save it for a revision 2.

I didn't get the gusset in the center yet, and I am not 100% certain I will go with the drop in U shape yet. I was thinking a structured I beam might be better. Still tinkering of course.

 

Rick--

I have been going over paddle wheel numbers using your excel spread sheet and there are a few of the variables I can't change without borking the formula in the affected cells. Namely blade depth and area.

I am including an image with the setup/size that would fit the current boat design best. I show the paddles submerged right to the water line for 8" of depth but I can make the paddles taller to prevent flow over the top etc. I could also increase the wheel diameter to 36" (.9144m) if I had to.

 

You have adequate blade area but the wheel immersion is enough to reduce efficiency. It will tend to lift a lot of water unless you articulate the blades.

The wheel model I did was aimed at efficiency while using fixed blades. I limited immersion angle to 60 degrees as a lead of 15 to 20 degrees on the blades will avoid lifting lots of water. Once you start lifting water you waste a lot of power.

So your wheel has enough blade area to grip without much slip but the simple spreadsheet does not have the sophistication to work out the losses to lifting water.

The diameter that I determined was larger than yours so you will need to pedal faster to get the speed potential but then the loss of efficiency will result in a lot more effort. The diameter you have is probably about right for a nice load but you will go slower than a wide, larger diameter wheel.

My guess is your wheel will have about 50% efficiency. If you articulated the blades you would get up around the 70%. An aggressive lead of 20 to 30 degrees might get it to 60%.

I only have actual data on one paddlewheel so I am interested in what you arrive at as it gives me more design data.

 

Just to make it clear with the spreadsheet. You can alter the blade area by increasing the width or the diameter. I have constrained it so it only allows 60 degrees of blade immersion.

If you look at old paddlewheelers that get high efficiency you will see there is only about 60 degrees of arc in the water. Immersing deeper than this means the blades lift water as they exit. This is doing wasted work.
http://new-brunswick.net/Saint_John/historic/pics/newbrunswick.jpg
http://www.pbase.com/moses76/image/78065408
http://lh3.ggpht.com/_Gxn-KDOthY4/R_eKXvypXoI/AAAAAAAAAQU/v2RZ1rJnBGc/IMG_0279.JPG

Having a high angle of immersion is a common design fault with low power wheels.

There are well-known methods of blade articulation to "feather" the blades on exit but it requires quite complex linkages. Tinhorn has no doubt got the original patent on this.

I would have thought 4ft wide wheel would be possible. Set the hull centrelines about 5ft apart and mount bearings off each hull. Run a crank rod along the line of each hull set at 90 degrees of rotation so they do not get locked.

 

Rick,
Could you explain what you mean by "lead" in reference to the paddle wheel blades? I'm still examining the conical wheel, so this is of interest to me.
Thanks,
Curtis

 

I am referring to the angle of the blades relative to the radial line of the wheel. The leading edge is angled forward. This gives the blade a flatter angle at entry and more vertical angle at exit. On average it will provide some uplift force and also reduce the tendency to lift water on exit.

The extra uplift is not highly desirable but it is preferred to down force that comes from lifting water.

I have not done any calculations on this or seen any measurement but you notice the good pedal paddlewheel competitors run with lead on the blades. One wheel I have seen on the web has feathering.

 

Curtis
You can achieve a similar result with reverse cupped blades. The blade may look intuitively wrong as they have slightly lower Cd than flat blade but they improve efficiency through better entry and exit.

Paddlewheels have not been very well developed with the current engineering tools but there is no reason why they cannot be efficient.

The attached is the only paddlewheel boat I actually have some rudimentary data on. Based on engine and achieved boat speed the wheels give no better than 60% efficiency. It would need much larger blades to improve efficiency. Wheels give an indication of required diameter for direct linkage to pedals and have about the right immersion:
http://snorlax.lampi.us/mike/dakanu.html

 

Still tinkering with the wheel design Rick. I will of course share any and all data we pick up along the way.

I have been watching the video linked earlier:

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

I have been staring at it for almost an hour now and I honestly just don't get it. Which of the 2 wheels are turning? It looks like they have the paddles axle in a track that follows the larger circles path...I just don't see that working.

I tried several designs using elastic (aka rubber bands) to pull the blades into a feathered position until water loaded them up...just not working as the stops are always in the way.

I am beginning to think any gains from feathering would be offset by mechanical losses and added complexity and weight.

Would you think more blades with a shallower draft would be better? Say a 30" or 36" diameter with 3" tall paddles submerged 4" deep. 12 or even 16 blades.

I also agree Rick that paddle blade shape is going to play a big role. Well designed blades might even make a feathering system a wash.

I may be able to go a little wider but not much. My plan is actually to split the wheel into 2 wheels side by side with one for each rider so that each rider can peddle at their own level.

 

There are two centres of rotation. Think of a main shaft across the boat with pivoting blades mounted off radial arms.

Now there is another wheel mounted outside the main wheel with offset centreline that has control linkages to the blades.

To get efficiency all the bearings would need to be low friction but it would be better than deep blades that are unfeathered. It allows you to reduce the number of blades and immerse the blades deeper to increase effective area without getting the high losses.

The best unfeathered wheel will be the maximum width you can fit in and diameter around the 1m mark. You need to find the best angle to set the blades.

 

Thanks, Rick, I'll keep that in mind. My progress so far with the conical wheels doesn't amount to a whole lot, but I have figured out that a 90 degree wheel is -- too cramped, for lack of a better term. I've drawn a 120 degree wheel, and it's much better for a given radius; I can get more paddle surface in the water.

Adding a lead angle to this configuration may or may not help it; as it is, the blades enter and exit obliquely, so they may not splash a lot. Trying to add lead . . . I'm not there yet. I'm going to try to fabricate a little model with six blades, and see what I can figure out.

Thanks again,
Curtis

 

Rick...

So the smaller diameter is basically just pinned to the side wall of the bigger diameter wheel on its axle then? It's free floating in the sense that there is no direct drive power to it?

I think the part I am not factoring into the motion is the resistance of the water maybe. Is that what gives the sort of...for want of a better term, "cam" action?

May be why I can't get the model to work as I can't apply that resistance load.

Curtis,

Keep us posted on your progress as your approach is very interesting. I am guessing by 120 degrees you mean the wheels in relation to each other?

 

No, that refers to the angle of the cone that it's built on. That first paper model I showed in the photos was the 90 degree cone; the 120 deg. is flatter, more spread out.

I'll try to put together a good presentation of the whole process when I get it done. It will be almost all pictures and text, almost no math. It may be a while, so be patient.

Curtis