I understand how complex it would be to exactly replicate a fish's tail
movement where much of the body is also part of the propelling surface.
I think that a simpler type geometry could still be quite effective
though. If you've ever seen a tuna or barracuda swim, they have a relatively
stiff body and both are known to be incredibly fast swimmers.
They typically don't seem to use much of their body as a propelling
surface but have fairly large tails and can "flick" their tails rapidly. I
spent quite a bit of time watching different types of fish swim in the
Monterey Bay Aquarium when I was contemplating this method of propulsion.
I did some sketches a few years back and even came up with a simple
mechanism using cables that would emulate the fish tail undulations.
The rear 1/3 of the fish's "body" and the tail section made up about 1/2
of the overall length.
With two pivot points and a flexible "skin" covering the moving section
it looked ( at least on paper ) like it could work.
I did another few sketches trying to copy a Manta ray's "wing" motions
and again, with a flexible covering it seemed like it could be done.
I abandoned the approach as I got more serious about building a sub
and settled on off-the-shelf Minnkotas because I just couldn't imagine how a
sub could use the whole idea in a situation where small forward/reverse
movements were needed, as would be the case if the sub was observing a fixed
object or trying to move very slowly in a confined area.
Still, for straight forward travel it could be useful if the
efficiency of power to speed could be developed to exceed a simple rotating
prop.
On a side note, I ordered the three Lenco electric actuators
yesterday to replace the old Firgelli ones I had purchased. Some adjustments
to the linkages and I should be able to install them on my two dive planes and
rudder assembly without too much trouble. The rubber bellows I have also fit
the new Lenco actuators and the Lenco's look a lot better made than the old
Firgelli's.
I hope to update my photo section on the projects page soon so I can
share the latest with you guys.
Frank D.