Warren's human powered boat 2008
Motion-Tech Needle HPB

I now have Rich Hodgkins' Motion-Tech Needle Surf-Ski. This is a 20 foot - 11 inch long, 16 inch wide racing Surf Ski that because of a combination of it's narrow width and high seat, nobody can paddle without capsizing. It looks to Rich and I as a perfect candidate to be HPB-ized. This one is yellow, and looks nicer than the one pictured below.

Current plans are to create a new twisted chain drivetrain that is lightweight and has some adjustment for leg length, as this will be a "record setter" class HPB. It will be used in combination with the skimmer outriggers as developed for the Necky HPB.

Motion-Tech Needle - Side

Motion-Tech Needle - Front

I'd like to use 1/2" pitch standard bike chain. One of the main reasons for using 1/4" pitch chain is that the smaller pitched chain can twist 90 degrees in a relatively short distance, and the 1/2" pitch chain does not twist as easily. To remedy this, you can loosen the side plates on standard 8 speed derailleur chain to allow it to twist in 1.5 feet.

The issue with 1/2" pitch chain still remains that  the drive leg is wider than it would be using 1/4" pitch chain. The twisted chain drive train page calls for a 1-1/4" tube, for a 10T 1/4" pitch sprocket. How narrow can I get with a 1/2" pitch sprocket?

Standard 12T sprocket width = 1.9"  (circumference = 12T x .5" = 6". diameter = 6" / 3.14 = 1.9")
Custom 9T sprocket width = 1.9"      (circumference = 9T x.5" = 4.5". diameter = 4.5" / 3.14 = 1.4")
Custom 6T sprocket width = .955"    (circumference = 6T x .5" = 3". diameter = 3" / 3.14 = .955")

6T probably would not be too efficient, so I can use the 1.5" tube and a 9T cog.

Because I want this boat to be race-able by other racers than me, it needs to have an adjustable seat to crank length. Also, someday this boat may turn into a hydrofoil, so I want to have the drive unit at about the CG of the boat+rider.

Recumbent bike style handlebars will either control the rudder, or control a steerable skeg for balance, in which case rudder control would be through the brakes, like the Wavebike.

Above is the concept for the new HPB. The crank assembly will be bolted to the deck between the foot wells. a series of mounting positions will allow multiple leg lengths. Drivetrain will be hard attached to the hull. Handlebars will be connect to the blue skeg control rod. Green is chain.

If I am using the 20" Heron prop, with it's required 2.7 to 1 drive ratio, that means I will need to use a 24T cog on the top of the drive. Using a cassette body will allow a couple gears. For an HPB at least two would be nice. One for sprinting and one for cruising.
* Drivetrain bolts into drive well in hull
* Gear changes to be accomplished via 2 or 3 speed gearing on cranks.

By using my angle grinder to cut down the end of the sealed BB axle so that it fits into the mounting hole in the cog, I have mounted the 9 tooth cog on the BB. Next I have to make a bracket to attach the prop to the other end of the BB driveshaft.

Note: Don't try to file a BB axle! They are made of hardened steel and will dull your file quickly.

The shell of the drive leg will be constructed from two fiberglass shell halves which I will form over a male mold and then bond together. While the distance from the hull bottom to the driveshaft will be only 16", the actual shell will need to be longer, as it will extend up into the boat for rigidity. Shell thickness will be 2 layers of 8oz fiberglass, plus a layer of Kevlar.
Today I made the parts that will become the prop end of the driveshaft. The part that goes on the square tapered shaft is a chunk of a front fork that I beat square. It worked nicely as it already had that tapered shape.

There is a foot of snow on the ground which is not conducive to brazing outdoors.

Bill Godwin is sending an old Wavebike canard stabilizer. I will be using that as the mold to build the shell of the drive leg.

I brazed up the new driveshaft. Now I need to find a bolt with the same threads as a BB bolt to keep it all together. In this picture you can see the keys on the prop shaft which will mate to the keyways cut into the prop to transfer the torque.

I experimented with some chain. Loosening the side plates on BMX chain did not really improve it's ability to twist. Sachs 8 speed derailleur chain twists 90 degrees nicely in 22", so I can figure on 24" from the prop shaft to the mid drive at the top of the drive leg.

I received the Wavebike canard stabilizer from Bill. It's a bit bigger than I remember, but should still make a great mold.
I brazed up the lower chain housing, and cut the slot for the chain. I also built up the intermediary jackshaft. I used a couple of spacers between the two gears to ensure they were far enough apart that the chains would not rub. I made a big lightweight spacer for the remaining space on the hub with some handy aluminum tubing.
I designed and brazed up the steel tubing frame to attach the upper and lower portion of the twisted chain drive. This will all be enclosed in the canard fin.

The jackshaft mounts to a steel plate, which attached to the two support tubes. Tubing clamps  allow the height of the frame to be adjusted, this allows the chain to be tightened.

I found that bike axles make good tubing clamp stock. The inner hole for the skewer is just the right diameter to tap out for a 5mm bolt. The axles are a bit harder than normal 4130, but perfectly cut-able with a hacksaw, and they braze fine.


I gave up on the twisted chain drive. It works, but not well. 1/4" pitch chain would have been better, but I have my doubts about how well it will last in the long run. This drive would work with more tweaking, but it would be more work than I have time for now.

Bill Godwin has come to my rescue again with more WaveBike boat parts. This time a Wavebike gear box and some other parts. This will help to simplify the drivetrain, and it should be fairly efficient. Below is a drawing of the design with 15 degree shaft angle.

Here's the actual boat, with the Wavebike gear box balanced on it. Bill recommends that the cranks be mounted to a short length of chain, which powers the gear box, rather than driving the box via the cranks directly. This way the gearing can be adjusted from the 3.13:1 that it is set up for. Charlie Ollinger recommends that the gearbox be mounted on the floor of the hull, as low as possible to get the best prop angle. Great ideas.
It's looking like I will need to remove the entire cockpit area to give me enough leg room.

To ensure the boat still has enough strength, I'll cover the inside of the new cockpit area, which will basically be the inside of the hull up to the front and rear bulkheads, with 1/2" foam, and then a layer of fiberglass. This will give me a firm structure to mount the seat into the bottom of the hull, and to mount the drive box and fore-aft adjustable crank assembly. This should allow a 5 degree shaft angle.
I'm planning on using 1/2" steel tubing for the driveshaft. This has worked well in the past.
I gave the heavy cast aluminum Wavebikedrivebox I got from Bill Godwin to Garrie Hill to be rebuilt with a CF carrier box. It used to weigh over 10 lbs.

He completely reconstructed it with new bearings.

He cut the output shaft out of the box, and sand blasted it.
He built a new box out of nomex honeycomb and CF.
He CFed in the bearing races.
Here's the new drive box. It's very light, and it spins great.

Testing of the Necky Kayak HPB shows that this narrower boat will need some type of outrigger, so I will build a single long skinny ama to provide stability.

Next step - Cut giant holes in the Motion-Tech Needle.




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