45 Hydro in a turn

[acaptn]

Could it be prop walk moving the back of the boat around causing the fin to wiggle some. Looks like the pulse is close to the prop pulse?

 

[ALLAN YUEN]

Look slow picture Same " Issue" Stress Viberation boom

 

[Tom Foley]

I think maybe I've solved the puzzle . It's caused more than likely by the Brake Lines from the staggered bending process on the Eagle turn fin . Next would be the flutter effect that is shown in the vid ? Interesting .

 

[Andy Brown]

This Twin 67-84 uses the same fin material thickness. Smooth flow.

Sure would be interesting to know the cause of the flutter. It's got to be over 15,000 cycles per minute.

Maybe it's in sync with the prop beats. Kinda like a micro prop walk like Rod mentioned.

 

[Elias Vazquez]

I think maybe I've solved the puzzle . It's caused more than likely by the Brake Lines from the staggered bending process on the Eagle turn fin . Next would be the flutter effect that is shown in the vid ? Interesting .

Could also be flexing or flutter from the turn fin.

 

[Elias Vazquez]

This Twin 67-84 uses the same fin material thickness. Smooth flow.

Sure would be interesting to know the cause of the flutter. It's got to be over 15,000 cycles per minute.

Maybe it's in sync with the prop beats. Kinda like a micro prop walk like Rod mentioned.

Awesome shot!

 

[Andy Brown]

I think maybe I've solved the puzzle . It's caused more than likely by the Brake Lines from the staggered bending process on the Eagle turn fin . Next would be the flutter effect that is shown in the vid ? Interesting .

I thought about the break lines , but the Sam's JRX shows the same phenomenon.

Got to be flutter. The pattern shows evidence of massive bite and lessor bite.

 

[KenOlvis]

I think maybe I've solved the puzzle . It's caused more than likely by the Brake Lines from the staggered bending process on the Eagle turn fin . Next would be the flutter effect that is shown in the vid ? Interesting .

I thought about the break lines , but the Sam's JRX shows the same phenomenon.
Got to be flutter. The pattern shows evidence of massive bite and lessor bite.

Is this a good phenomenon are a bad one?

The boats having this phenomenon are doing great during its appearance. Or would they do even better?

 

[Ian Inverarity]

This Twin 67-84 uses the same fin material thickness. Smooth flow.

Sure would be interesting to know the cause of the flutter. It's got to be over 15,000 cycles per minute.

Maybe it's in sync with the prop beats. Kinda like a micro prop walk like Rod mentioned.

Andy, my shots are taken with 1/2000th of a second shutter speed to try to freeze the boats and most of the spray in the shots. It isn't fast enough to freeze the props. I'm guessing this shot is taken at quite a bit slower shutter speed? This would not show the pattering in the spray.

 

[Ian Inverarity]

Here is a different boat turning:

https://flic.kr/p/xvdngr

Another:

https://flic.kr/p/xvdjUH

 

[Ian Inverarity]

Another gas boat, pattern in the turn fin spray but not as clear as Aron's:

https://flic.kr/p/xCHAJd

 

[Ian Inverarity]

About the closest I can find, a gas sport hydro at the NAMBA Nats :

https://flic.kr/p/vsthRr

 

[sbowden21]

I think maybe I've solved the puzzle . It's caused more than likely by the Brake Lines from the staggered bending process on the Eagle turn fin . Next would be the flutter effect that is shown in the vid ? Interesting .

I thought about the break lines , but the Sam's JRX shows the same phenomenon.
Got to be flutter. The pattern shows evidence of massive bite and lessor bite.

Virginia Craftsman turn fin as well..

 

[Ian Inverarity]

Counter examples, a very stiff twin with a stiff turn fin:

https://flic.kr/p/vsAW9D

A big 90 single, note the boom flex under the load of high speed turning! :

https://flic.kr/p/woNoZA

 

[Andy Brown]

About the closest I can find, a gas sport hydro at the NAMBA Nats :

https://flic.kr/p/vsthRr

I used to think it was caused by choppy water, but the shot of the gas sport on relatively smooth water and Aron's boat also moving through smooth, solid water prove that some kind of oscillation is going on with the fin.

 

[charles siler]

Sense we are running single piston motors could it be motor vibration?

 

[Terry Keeley]

Sense we are running single piston motors could it be motor vibration?

Hmmm. The pattern (frequency) looks similar to a prop rooster tail.

Wonder if it's different types of motor mounting transferring vibs to the fin causing some movement (flutter)?

 

[charles siler]

Sense we are running single piston motors could it be motor vibration?

Hmmm. The pattern (frequency) looks similar to a prop rooster tail.

Wonder if it's different types of motor mounting transferring vibs to the fin causing some movement (flutter)?

Arons motor is a stock new style CMB Evo.

 

[KenOlvis]

Harmonic effect by vibration

 

[Ian Inverarity]

The gas sport hydro and 45 hydro would have vastly different stiffness, I would expect resulting in quite different natural frequencies for the fin. I have been wondering if what we are seeing is the result of a cavitation bubble opening and closing on the outer surface of the turn fin?