wiggle drive propulsion application

[kjell]

Propeller propulsion or tail propulsion?
It is difficult to compare apples with oranges.

[mydauphin]

Efficient is such bad engineering word. More efficient at 2 knots in a canoe, vs 50 knots in a patrol vessel or 20 knots in 900 foot container vessel.

Many things won't scale properly, bumble bees, flies, birds all can not be built bigger.
Same will happen with high speed wiggle drives. But they still have their uses.
Ocean crossing drones, Canoes, perhaps propelling barges but as speed and size increases it becomes a more technical challenge to move those fins back and forth. In the small power boat examples, I believe we are seeing cavitating blades here, they are just not rotating all the way around.

[kjell]

Can you explain what do you means with cavitating blades?

[kerosene]

http://en.wikipedia.org/wiki/Cavitation

earlier you referred to cavitations as some kind of features on the prop blades (if I understood correctly). I have never heard of this. I think everyone here is referring to phenomenon where in low pressure side of a blade the gas in water or water itself creates bubbles.

[kjell]

http://en.wikipedia.org/wiki/Cavitation

Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Inertial cavitation occurs in nature in the strikes of mantis shrimps and pistol shrimps, as well as in the vascular tissues of plants. In man-made objects, it can occur in control valves, pumps, propellers and impellers.
Non inertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Such cavitation is often employed in ultrasonic cleaning baths and can also be observed in pumps, propellers, etc.
Since the shock waves formed by cavitation are strong enough to significantly damage moving parts, cavitation is usually an undesirable phenomenon. It is specifically avoided in the design of machines such as turbines or propellers, and eliminating cavitation is a major field in the study of fluid dynamics.

[kerosene]

my link was not the greatest - way too broad for this context. Cavitation in relation to airfoils (props and fins) was explained well several pages back.

[kjell]

Horizontal Tail Drive.
This is my latest designs. In upper and lower position the tail is lined to the water flow.

[A.T.]

Originally Posted by kjell

Horizontal Tail Drive.
This my latest designs. In upper and lower position the tail is lined to the water flow.

Not sure if I picture this correctly, but wouldn't this create periodic vertical reaction forces that would shake the vessel. I guess it doesn't matter for models, but any wiggle-drive design for a manned boat would have to make sure that not the entire boat is wiggling.

[kjell]

The idea is to drive this Tail Drive at a faster frequency than the boats wiggling frequency.

[Frosty]

Originally Posted by kjell

Horizontal Tail Drive.
This is my latest designs. In upper and lower position the tail is lined to the water flow.

Now all you need to do is make it rotate.

[kjell]

This Drive is not for speed boats. It can run forward and reverse. It is deigned to be installed in desplacements boats and Catamarans with rudder installed.

[Frosty]

If you got it to rotate it would give constant thrust without vibration or jerking motion.

The fins could be a fixed pitch giving max thrust, altering rotation would give reverse. I think you've got something there,-- its called a propeller

[kjell]

Why do you think it is a good idea to use a tail drive as propeller,rotating it?

[A.T.]

Originally Posted by kjell

The idea is to drive this Tail Drive at a faster frequency than the boats wiggling frequency.

Doesn’t the frequency of the drive depend on how much thrust you need? How to avoid that it hits the boats wiggling frequency at some thrust setting?

[kjell]

Originally Posted by A.T.

Doesn’t the frequency of the drive depend on how much thrust you need? How to avoid that it hits the boats wiggling frequency at some thrust setting?

The boat wiggling frequency is slow and drive wiggling frequency is fast. It nearly impossible that they will come in harmony.