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PostPosted: Thu Dec 06, 2012 8:23 pm 
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Joined: Wed Sep 02, 2009 1:14 pm
Posts: 20
Location: Moab, Utah
I am looking for ways to reduce the knee pain I sometimes get from long or hard pedaling. The Mirage Drive system is most closely akin to a stairstepper machine, which is known to be somewhat hard on knees, as opposed to the circular motion of a bicycle or elliptical.

Aside from simply going slower or going fewer miles, I sometimes employ my arms by gabbing a fistful of wetsuit just above the knees and pushing and pulling. This helps some.

Back in 2009, JeffreyET wrote about his experiment with making longer pedal shafts (viewtopic.php?f=11&t=13835&p=76843&hilit=pedal+aluminum). I haven't read any more about this idea, and I'm wondering if anyone else has tried it and what the results are. What are the theoretical advantages and disadvantages (I'm not much for physics)?

It seems to me the greater leverage of the longer shafts would mean more power or an easier stroke, but possibly they would put my feet too far up in the air or too far forward or in some awkward position.

I assume Hobie has some good reasons for making the shafts the stock length, but might other lengths be better for some people or some uses?

Thanks for your thoughts.


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PostPosted: Sun Dec 09, 2012 6:57 am 
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Joined: Tue Sep 04, 2012 2:23 am
Posts: 33
Location: Mandurah, Western Australia
Hi there.

Have you tried adjusting the setting on your pedals? I know some owners alter their length of stride a couple of times throughout the day to reduce fatigue on their joints.

Oatesy.


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PostPosted: Sun Dec 09, 2012 7:31 am 
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Joined: Mon Apr 26, 2010 6:06 am
Posts: 736
Location: Amelia Island, FL
I have a knee problem that comes and goes. When it does bother me I usually just shorten my pedal motion rather than long sweeping motion of the fins.


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PostPosted: Sun Dec 09, 2012 8:32 am 
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Joined: Sun Apr 20, 2008 6:18 am
Posts: 1444
Location: Sarasota,Key West FL
Microboater:
I also have knee problems if I over do it on the pedals. I use the turbo fins, and use much shorter strokes, I have the pedals set so my fully extended leg does not bottom out the pedal. I use low force steady pedaling and can easily pedal for ten hours if needed. Instead of trying to go 4-5 mph and driving hard, I settle for a easy slow rate (2-3 mph).
Pedaling this way your knees hardly bend at all, and the strain on them is much much less, with the turbo fins you can pedal much slower with less strain on your knees yet get much more propulsion force with much less effort.
My wife and I have had many Hobie Kayaks over the years and always take the sails along with us (they stow on the bungie on the side of the hull), and use the sails whenever there is any wind (even on rivers).
The Hobie sail kit allows you to double/triple your range. A good day for us can be 20-30 miles (even just a little wind helps). With a combination of paddling, pedaling, and sailing we switch it up often so we are not over doing any single muscle group, and most important we are not trying to win any races, you can easily poop yourself out in a few hundred yards.
You will find that when pedaled properly a Hobie will go farther with much less effort than you could ever do with paddles or any rotary pedal system.
Hope this helps you.
Bob


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PostPosted: Sun Dec 09, 2012 8:58 am 
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Joined: Mon Apr 26, 2010 6:06 am
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Location: Amelia Island, FL
While different things work for different folks, I recommend that you not fully extend you legs when pedaling. Like riding a bicycle, it will take stress off your legs/knees.


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PostPosted: Sun Dec 09, 2012 9:50 am 
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Joined: Wed Sep 02, 2009 1:14 pm
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Location: Moab, Utah
Thank you all for your good suggestions and reminders to do what I often neglect to do, like taking it slower or varying my stroke lengths etc. So are you saying that there is a greater stress on the knee (over a given distance) when you extend the knee almost fully than when you keep it more bent?

On the other topic, does anyone understand the physics of this enough to suggest whether having the added leverage of longer crank shafts would reduce overall stress? I am intrigued by the idea.


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PostPosted: Sun Dec 09, 2012 9:53 am 
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Joined: Sun Apr 20, 2008 6:18 am
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Location: Sarasota,Key West FL
islandspeed2001:
I agree 100%, I was only using the stretched leg example as a way to set his pedal length, most new users when going out for the first time with us tend to set their pedals way too close to their body and pedal like you would a small trike with their knees all crunched up, and they use the whole stroke banging the fins against the bottom of the boat and get tired very quickly, with the fins rotating over 180 degrees, I was just suggesting he can get just as much propulsion with a shorter stroke (120 degrees = 60 degrees per fin) with less effort and knee bending, and most important pedal slow and easy strokes.

What I was trying to say was when your leg is fully extended the mirage fin should be just short of the bottomed out extreme of the pedal so it is not possible to bang the bottom of the boat with the fin. Then when pedaling use half of that stroke, your knees remain bent. Sorry if I discribed it incorrectly.
Bob


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PostPosted: Sun Dec 09, 2012 1:18 pm 
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Joined: Mon Apr 26, 2010 6:06 am
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Location: Amelia Island, FL
I do like you comment that with you leg extended, the fins should not quite touch the hull :!: That would certainly keep from having the fins banging against the hull. I gotta check out my own set-up


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PostPosted: Sun Dec 09, 2012 4:28 pm 
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Joined: Sun Aug 12, 2007 5:17 pm
Posts: 539
Location: Auckland NZ
Longer pedal shafts would raise your feet higher & IMO could end up being uncomfortable.

Smaller fins would give the same result (i.e. reduced gearing).

I assume you are already using just the small fins (and not the STs or ST Turbos)? If not: convert to the small fins!

If you are already on the smaller ones, still experiencing knee pain, and have adjusted the drive to ensure that your knees are not over-extending you might want to try further reducing the gearing simply by trimming some area off the fins - I can't imagine that carefully cutting some off the trailing edge would seriously affect their reliability in operation and it would mean that you have less water to push on each stroke - i.e. reduced gearing.


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