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Topic: Current HPB prop design, Another by Rick Willoughby...< Next Oldest | Next Newest >
Capn Jimbo Offline
The Godfisher

Group: Super Administrators
Posts: 1712
Joined: Jan. 2004
Posted: Jan. 15 2009,06:47

Warning! Due to its banana-shaped profile, this post may be hazardous to monkeys who may try to eat, rather than pedal it!

Pictures speak louder than words, so...

Rick Willoughby is one of the driving forces behind the wonderful - and serious - HPB (Human Powered Boat) group.  Even Hobie's big Kahuna, Greg Ketterman, was once an active member when he was stuck in his design.  Not that he'd admit that now.

Rick's prototype design is quite impressive, and is the latest progression of about ten designs.  He has spent much time creating an extremely fast hull that offers minimal resistance - adjustable outriggers provide needed stability.  He has experimented with quite a number of drive systems and prop designs, constantly seeking improved performance and reliability, with light weight.  Let's look closer...

Let's start at the stern and work forward.  Needless to say, this is a very high performance hull, with sharp entry and exit.  The twin rudders are retractible and effective, and drop into the water stream only when needed.  Otherwise, they are up to reduce drag.  Neat.

The outriggers are also retractible and adjustable from full down to full up.  Other than at rest, I'm sure the traveling position is up enough to clear the chop, while still preventing capsize.  At rest, this craft could be made quite standable.

The drive is Rick's latest design and is both effective and simple. Not only is a reclining position comfortable, it allows a powerful and continuous transfer of power to a constantly rotating drive and prop.  I won't bore you but please know that the typical circular bicycle drive is the most effective, least tiring means of transferring power.  Circular always beats linear.

The transfer from the pedals to the driveshaft is simple, sturdy and exhibits minimal friction and/or loss of power.  Rick has used a spring steel driveshaft - brilliant.  Flexible and designed to provide an unlimited, repair-free life.  And boy is it effective!  No loss of power through power robbing gear trains, sealed bearings, drag inducing structures or complex mechanisms (like flippers, ugh).  

The result: maximum power delivered to a prop designed specifically for its human powered purpose.

Last, Rick states the prop can easily be swung up and just behind the backrest for use in shallow water.  No muss, no fuss, easily done, even underway!  Great stuff, Rick.

Bottom line:

The Hobie dingbat drive was never, and will never be a really effective drive.  Studies done by some talented folks over at HPB found the drive varied between 25-40% efficiency, mostly due to turbulence and the constantly changing motion of the flipfloppers.  Compare to prop drives that routinely transfer power at 70-90% efficiency.  No wasted effort, better transfer, faster.  And don't get me started about Hobie's breakdowns.

In closing, do keep in mind this is a prototype, but anyone with half a banana can imagine the possibilities...


Tight lines,
Capn Jimbo

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0 replies since Jan. 15 2009,06:47 < Next Oldest | Next Newest >

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