Re: [PSUBS-MAILIST] bionic propeller

Hi, Frank,

As you mentioned, a larger diameter prop is somewhat more efficient than a smaller one. The problem is that it bumps into things and otherwise gets in the way.

The movement of a fish tail is complex; much more to it than just wagging back and forth. It undulates to an extent, carries the motion all the way to the head of the fish, and varies that motion depending on that the fish is doing -- cruising, darting, turning, etc. The biggest advance in understanding the dynamics comes from having computers that can now measure multiple motion points on the fish and analyze it in all its variations. The other half of the problem is constructing a mechanism that can duplicate that motion (again, in all its variations). As you pointed out, it would be a lot easier to configure cruise mode.

You may have seen boats used in the orient that are propelled by a long, hinged oar that is wagged back and forth at the rear of the boat much like a fish tail. Sorry I don't know what it's called. The oarsman is standing and the boat rocks back and forth with each stroke. I've only seen them in National Geographic type films. Maybe someone has eyes-on experience.

Take care,

Jim

In a message dated 11/19/2010 8:41:39 P.M. Central Standard Time, ShellyDalg@aol.com writes:

Hi Jurgen.

I've had some thoughts on these over the years but never actually built anything.

It seems possible to make a highly efficient propulsion design if a "fish like" concept could be fabricated.

I don't think it would be very useful for close-in maneuvering but could be good for longer distance traveling.

Vance said once that one of the "Perry" boats he piloted had a large prop and with just a small rotation could move the boat quite well.

The point I'm making here is that a fish's tail is a large surface compared to the whole, where as a small but fast spinning prop is a relatively small surface compared to the whole.

There are some "toys" that you can get that are shaped like fish and swim by moving the tail.

It could be fun to make a few different fish type models to see how they perform.

By using flexible materials, and cam type mechanisms, it doesn't seem like it would be too difficult or expensive to investigate.

Sounds like FUN !!!!!

Frank D.