November 2, 2006


The twisted drive, and Las Vegas marathon
(click pictures to enlarge)

I have been SLOOOWLY cleaning up the shop over the last month or so. I gutted it, cleaned everything, then slowly moved stuff back and put it all where it could be found once again. I love an organized shop. I bought some new bins at Home Depot, and a bunch of blank sticky labels. Now I have a bin for everything - bottom brackets, headsets, clamps, hinges, velcro, tape, glue, funny shaped things that look like this, etc, etc... It really helps when you are building something or prototyping. To have a part, a special fastener or a piece of tubing that's already bent a certain way is very handy. I thing it's really part of the creative process - to be able to envision something and then just build it using stuff you have in a bin somewhere.

And this is what a well organized, well equipped shop will get you:

This is a drive leg for the prototype boat. I built it in less than a day using parts and materials from my many little magical bins. Plus, it EVEN includes a prop which I 'borrowed' from my Shuttle bike human powered bike kit.

The prop bolts onto a Shimano octalink sealed bottom bracket cartridge that is screwed into a bottom bracket shell. The BB shell is welded to the end of my drive leg shaft - a 2" x 1" rectangular Chrome Alloy steel tube. The other end of the bottom bracket cartridge is a Shimano Dura-ace 11 tooth cog from a bike rear cassette. I welded a round plate to the back of it, drilled a hole in it and bolted it to the bottom bracket cartridge.

The chain is Shimano 9 speed Ultegra which twists up the drive shaft to a 39 tooth chain ring on a Shimano sealed bottom bracket cartridge with two brackets welded to the BB shell. 4 bolts secure the bracket to the rectangular shaft allowing the chain ring / cranks assembly to slide up or down the shaft for various lengths

A take-up pulley guides the chain down to the small cog.

I can pedal forward or backward and because my main chain ring is adjustable, I can take out all of the slack in the chain and the chain stays on the gears.

The plan is to sand down the cromaloy steel and coat it with epoxy or powder coating. For extra water proofing, I could wrap a couple layers of fiberglass/epoxy around all of the tubing which probably wouldn't be a bad idea. The bottom brackets are sealed and should withstand prolonged periods of being submerged under water. At least, that is the experience of others who have used standard bike bottom brackets as bearings for props. Mountain bikes can take quite a bit of mud, dirt, water and torque and a decent quality bottom bracket cartridge will last for years.

The best thing about using standard bike parts is they are all easily replaceable. If the chain goes, it can be replaced with a new chain, or replacement links can be added. If a bearing fails, the entire BB cartridge can be removed with a standard BB wrench. I could carry 3 or 4 or even 10 spare replacement parts - they are all very light weight and take up very little space. This entire system could easily be overhauled - even on the water if required. Well, that's the idea anyhow - and one of the purposes of this first drive leg.

I will need to make a fairing for it to keep the water out of the spinning chain. Ill probably wait until I know exactly how this drive holds up under some decent abuse before making a fairing.

There are a few obvious issues with this first drive leg design. Mostly, it appears to be a lot wider than I thought it would be and that will make it less efficient as it slices through the water due to the extra width of the fairing that needs to cover it all. Since I wanted to keep everything 'standard bike stuff', the main chain ring is offset to the right (typical bike mechanical geometry), but the prop is directly below in the center. Therefore the chain near the top is further to the right than where the chain is at the bottom where it joins the prop. I'm not sure how to re-work this, or even if it's necessary.

The main purpose of this drive leg is to TEST it!! I Want to know for sure that the twisting chain will stand up to at least 500 hours of use in salt water. I am going to mount the drive over a large bucket filled with salt water and rig an electric motor up to the crank. I'm going to replace the chain ring / cranks shown with my SRM power meter so I can set the speed of the drill to approximate my typical power output which will be about 150 watts. In fact, I'd like to overshoot that for this test and run it 24/7 at 200 watts to see what wears out.

I am going to sand down the metal parts and paint a coat of epoxy over them to protect the steel from the corrosive effects of the salt water. My plan is to run the chain directly through the water and make sure that it is always well oiled via daily lubrication.

The drive leg that will be used on the boat will be mostly water tight and I would like to use stainless steel, so I don't expect too much salt water to ever even touch the steel or the chain, but I want to get an idea of what the worse-case abuse would be. What if my fairing cover over the drive leg is smashed, or develops a bad leak and everything gets permanently soaked in sea water? I want to have some idea as to what would happen and how all of the parts would handle that kind of exposure.

I'm going to run some numbers through JavaProp and design my own prop. Rick Willoughby has been making his own props by bending stainless steel plate like Cory Schaffhausen's home made prop.

Las Vegas marathon

I am recovering fast from my sub par performance at Ironman Hawaii - in fact, if it wasn't for my bad ankle, I felt like I could have done another Ironman 4 or 5 days after finishing Kona (not that I would want to!). I think that shows you how hard I really DIDN'T go in Hawaii.

Helen and I are doing the Las Vegas Marathon on Dec 10th. I've been slowing getting my running back - starting with plenty of elliptical trainer, then moving some volume to the soft tread mill, and slowly doing more track running. I'm at the point now where 50% of my running is on the track and the other 50% is split between the elliptical and the tread mill. But, my ankle is healing, so I think I'll be OK for the marathon.

My goal is to break 3:20. My best marathon time is 3:15, but all I need to re-qualify for the Boston Marathon is a 3:30. The deal Helen and I have is we will only both go to Boston if we can both qualify. She just did the Portland marathon and missed her 3:50 qualifying time by 2 minutes! I think she just might do it in Vegas, so I better do it as well.


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