The Whittaker Paddle Wheel

The Whittaker style paddle (video) wheel uses off-axis blades to increase efficiency and eliminate fouling. It is ideally suited for amphibious projects and applications where weeds would tangle in a normal propeller. It is low-draft and works well whether the blades dip just 3" into the water or go as deep as 13". Here's how I made one using a recycled plastic barrel and a bicycle crankset.

What you'll use up:

1 large plastic barrel (HDPE) (the one in this Instructable is probably 30 to 35 gallons)
[NOTE: I've since learned that the BLUE HDPE barrels are far less prone to fracturing than the WHITE barrel shown in ths instructable-- so use a blue barrel if you can!]
A couple of lengths of 2x2 redwood
About 2 feet flat steel approx 1/8" thick,1-1/2"
Bicycle crank, 3-part style (the pedals come off the spindle)
30 stainless steel wood screws and 18 fender washers
Rust-inhibiting spray paint

Tools:
Welder
Cutter/grinder
Saws-all or scroll saw or keyhole saw
Driver or screwdriver
Table saw or mad skills with a circle saw

Here's an outline of the steps:
1) Build a couple of triangles from the wood, 20" (ish) on a side.
2) Cut and weld the crankset to fit into the triangles. Screw the armatures to the triangles.
3) Cut 6 paddle blades from the barrel. Make them 1/6th the circumference of the barrel and 20 to 24" long.
4) Screw everything together.
5) Mount to your amphibious vehicle.

1) Cut 6 pieces of redwood 18.5" long and having ends that are cut at 60 degrees. Redwood resists rotting in the water pretty well, so don't treat it.
2) Optionally, bevel the outer faces of these pieces. The paddle blades enclose an arc of 60 degrees because they are cut from 1/6th of a barrel (which is 360 degrees total), and a bevel of 15 to 30 degrees will help to level them out so the thrust leaves straight to the rear of the paddle wheel. If the plastic did not flex ever, then 30 degrees would be the correct angle. Because it does flex, the angle is somewhat intuitively determined.
3) Offset the corners of the triangles, and predrill and screw them together. Predrilling is important in brittle redwood. Now you've got a pair of triangles just over 20" on a side. Assemble them so there's a right and a left (see the drawing)
4) Turn the triangles so the bevel faces down and mark the centers of each leg of the triangle (approximately 10 -1/4" from the corners) to help with aligning during metal fabrication step.

Note: the blades extend past the corners of the triangles... so knowing the left triangle from the right triangle is important. Also, since we are mounting the edge of the blade to the triangles, it's important to make sure your blades point away from the axle so that the blades clear whatever frame you will build. Keeping this in mind will help you orient the bevel correctly.

Take your 3-part pedal crank apart. You'll probably need a hammer or a blowtorch to remove the crank arms from the axle- those things are really good at staying assembled.

1) This pedal crank set had 6" arms, so I cut a set of 4 steel plates from 1/8" stock 1-1/2 x 5-3/4 to match.
2) Grind or cut a semi-circle out of one end of the plates, to fit the curve of the crank where it bolts to the axle (as shown in the picture).
3) Add a small bend to the other end of the plates. The cranks have a slight angle to them, and you need to match it so your triangle will mount straight up and down and not wobble about.
4) Drill holes* about 3/4" from the ends of the cranks and plates so you can attach them to the redwood triangles.
5) Test fit everything, and then predrill and screw the plates and cranks to the triangles. The crank with the gearset mounts to the right triangle, and the other mounts to the left triangle.
6) The center of the diamond shaped hole in the cranks will be about 12" from the corners of the triangle. Shift stuff around until you're close to center. There's no real penalty for being off; water is far more forgiving than land. Use the axle to help you make sure the entire armature is as close to center aligned as possible as well as making sure it's as close to square/perpendicular/whatever it is called to have a thing rotate in a single plane instead of wander about, nutating around an axis.
7) Tack weld the plates to the pedal cranks.
8) Take the triangles off and weld it all up.
9) Paint the metal with a rust inhibiting paint
10) Re-attach the metal armatures to the wooden triangles.


*To drill a hole in metal with woodworking tools, go very slow and use WD40 or 3inOne oil to lubricate the bit. If you can get long curls of metal to spiral up out of the hole, you're doing in right. Don't hurry or you'll snap the bit. If your drill bits are any good at all you'll be fine and not damage them seriously .