Comments on: Mahalo!

By: Philip Chadez

Philip Chadez — Mon, 21 Dec 2009 09:51:08 +0000

Nice level of information here. There is so much data around about this subject that sometimes you cannot see the wood for the trees but you have pitched this at just the right level so that the lay person can understand – thank you!

By: Frank

Frank — Thu, 29 Oct 2009 17:32:37 +0000

I found this to further clarify what Peter said:
http://answers.yahoo.com/question/index?qid=20080921173739AAta1i8

By: Peter Raymond

Peter Raymond — Thu, 29 Oct 2009 15:36:37 +0000

As a mechanical engineer I agree that it’s important to test, but with the break happening so quickly, that indicates that there was a design problem.

The force you can apply at the pedals and the gearing lets you calculate the shaft torque. The radius of the shaft will give you the shear force that the shear pin has to resist. The area of the pin will give you the shear area, so you can calculate the shear stress that the pin has to resist for normal use. I would recommend assuming that only one side of the pin is carrying the full load and look for at least a factor of safety of 5.

A little harder is to figure out what would happen if the prop was spinning at full speed and a stick got stuck in the prop. You might want to try testing that on land.

In outboard motors there used to be a shear pin in the prop. If the prop hit a rock the pin was designed to shear and to be easy to replace. As I recall, the pin was under a removable cone on the back of the prop shaft. I think that now most outboards have something that will limit torque and allow slip if the load gets too high.

For your use I think a prop shear pin would be fine, but you would like it to be easy to replace and it should be designed to be the first thing to break. Of course, you also need to carry spares.

By: Bryon Howard

Bryon Howard — Thu, 29 Oct 2009 15:24:15 +0000

Way to power into those Waves Greg.
Good to hear there were no problems with control, speed into the wind, or powering through.

Been thinking about squeezing into the cockpit … and am inspired to get on my bike trainer!

By: Frank

Frank — Thu, 29 Oct 2009 14:43:24 +0000

While running 24/7 for months is a good test, and I would recommend that you do so, I would also include other testing along the lines of what Guy suggested. I.e. you need to subject the system to shock waves, abrupt starts and stops, abrupt reversals and other high frequency transients. Those are more likely to cause the types of breakage that you experienced recently.

By: Guy Gilbert

Guy Gilbert — Thu, 29 Oct 2009 11:50:18 +0000

In my opinion, the drive system should be able to resist to human legs while the propeller is trapped in a fishing net. This would be the ultimate test.

By: David Tangye

David Tangye — Thu, 29 Oct 2009 11:32:13 +0000

Those sort sharp lake waves are an excellent test for the ocean. Waves in shallow water, near land, in tidal areas and coastal points are mostly more confused and usually tougher to handle for small craft than when way offshore, where they might be mountainous but are also likely to be long and nice and predictable (except every 1 in 10,000 ).

By: dennis

dennis — Thu, 29 Oct 2009 05:33:41 +0000

You guys are having quite the adventure, thanks for all the updates. Love to follow. Good luck tweaking the drive system. Thanks for sharing.