The fin is indeed an efficient and elegant solution. The conceptual inefficiency is the energy lost to the back-and-forth momentum changes of the fin mass. Rotational propulsion avoids these loses, but organic biology is incapable of continuous rotational exertion; muscle fibers would get "all twisted up in the game." Rotational propulsion has bearing losses, and higher water friction losses from the faster moving parts. Low speed lightweight fins could likely outperform smaller high speed propellers in terms of more efficient use of available energy.
love the mind games,
Mark Stafford
--- In electricboats@yahoogroups.com, "jpz@..." <johnzimmerlee@...> wrote:
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> The fin drive was developed a few million years ago in fish with opposing muscles. That technology lends itself to two human leg muscles replacing the opposing fish muscles. It is not very efficient but works on designs created before the wheel.
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> What makes Mirage worthy is that the human legs are more powerful that human arms, and the human legs are accustomed to pumping or running. In addition, by forcing one foot forward and relaxing the other . . . the fins retract up against the hull for beaching. Also, fins operate at slower speeds and are not susceptible to ventilation & cavitation like props near the surface. The downside is that the balls of the feet are used on the pedals and it becomes tiring with your feet held high in the air. The other major disadvantage is the loss of reverse motion.
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> More efficiency comes with a sprocket, rotary motion, and a prop. This results in higher speed,less effort, and available reverse . . though reverse is only a third the efficiency of forward. The prop must be at least a diameter distance below the surface to avoid cavitation. The requires a running depth of 20" for the average trolling motor.
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> Adding electric power is difficult in fin technology in that the rotary power must be converted to a pumping or piston action. Reverse is still not possible.
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> Another technology is emerging eventhough it is more than 2000 years old. It is Archimedes screw (augers)and offers instant response in both forward and reverse motion. Attached to opposing trolling motors mounted midship, the augers provide efficient low speed operation and can be completely controlled by one's feet . . . leaving the hands free all day for fishing, hunting, bird watching, etc. If the hull is designed correctly, running depth is only 10".
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> You can see this patented technology it in action at http://www.youtube.com/watch?v=3sZ8cKelDRs
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> John Zimmerlee
>
> --- In electricboats@yahoogroups.com, Mike <biankablog@> wrote:
> >
> > Joe:
> > Â
> > The Mirage propulsion is an interesting design. If I ever find the time I was thinking about building a dingy that might incorporate the unit. The only problem I see about converting it from feet to motor operation is that there is more moving parts involved than the prop, shaft motor/engine standard. I could be wrong but, I'm not sure it would hold up at higher speeds for very long.
> > Â
> > Capt. Mike
> > http://biankablog.blogspot.comÂ
> >
> > --- On Fri, 1/28/11, Joe <jtolmanmitchell@> wrote:
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> >
> > From: Joe <jtolmanmitchell@>
> > Subject: [Electric Boats] has anyone ever had experience with fin drive propulsion?
> > To: electricboats@yahoogroups.com
> > Date: Friday, January 28, 2011, 8:17 PM
> >
> >
> > Â
> >
> >
> >
> > ...like the Hobie Mirage kayak but motorized. as far as human powered propulsion goes it seems to be the most efficient. why would this not hold true to to electric motorization? has anyone had any experience with this?
> >
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