45 Hydro in a turn

[stan simpson iv]

I will Protest the first boat I see at the next race that does this... HAS TO BE ILLEGAL!!!

 

[KenOlvis]

I will Protest the first boat I see at the next race that does this... HAS TO BE ILLEGAL!!!

Lmao some will try to duplicate by adding who knows what on to there boats

 

[Niklas Edlund]

The easiest way to get rid of the fin flutter, of course, is to have a boat that doesnt slide in the corners...

 

[Ian Inverarity]

The easiest way to get rid of the fin flutter, of course, is to have a boat that doesnt slide in the corners...

Niklas, the slide can be minimised but not eliminated! Minimising should always be the aim of course!

 

[dwilfong]

every time the prop hits the water it loads the fin . when it leaves the water it unloads the fin. I am thinking a good performing prop in the corners will load the fin more making a more pronounced pattern? Also the performance of the fin will make it more dramatic?

 

[Danny King]

every time the prop hits the water it loads the fin . when it leaves the water it unloads the fin. I am thinking a good performing prop in the corners will load the fin more making a more pronounced pattern? Also the performance of the fin will make it more dramatic?

 

[Danny King]

every time the prop hits the water it loads the fin . when it leaves the water it unloads the fin. I am thinking a good performing prop in the corners will load the fin more making a more pronounced pattern? Also the performance of the fin will make it more dramatic?

This is what I was thinking too. A great experiment would be to photograph a rigger the same day. One with a 2 blade and then a 3 blade prop. That has to be where the pulse are coming from. Even at 30,000 it is a series of very fast pulses which to our naked eyes seems seamless. But isn't. Same way a acoustic rpm meter works. To our ear it's a constant noise. But it isn't. But a test with a 2 blade and a 3 blade prop should show differrant patterns.

 

[Tom Foley]

LIKE . Put a high speed Go Pro in there with something to measure vibration .

 

[shoboat]

Danny,

A four bladed propeller would be even smoother to test with?

Does someone have a 67-Hydro to try and see if the fin pulsing can

be reduced with a different propeller set up?

I have some propellers for the test? Anyone want to try this?

Let Me Know?

Mark Sholund

231-590-3023

Email is: [email protected]

 

[dwilfong]

Now take a fin that flexes???

will it absorb the pulse??????

will it hold better not loading and unloading the water off the fin changing the pressure point????

Things that make you go HUMMMMMMMMMMM!!!!!!!!!!!

 

[Danny King]

Danny,

A four bladed propeller would be even smoother to test with?

Does someone have a 67-Hydro to try and see if the fin pulsing can

be reduced with a different propeller set up?

I have some propellers for the test? Anyone want to try this?

Let Me Know?

Mark Sholund

231-590-3023

Email is: [email protected]

I agree Mark but a 3 blade is taboo enough. Lol. A four blade would be even smoother.

 

[dwilfong]

I noticed that the boat in question has a thick stiff Virginian craftsman fin on it. also the gas boat has a thick stif fin on it.

Any pics of a SGX with the stock flexible thin fin????????

 

[KenOlvis]

The first post is pic of SGX

 

[Brad Christy]

Guys,

For the loading/unloading cycle of the prop to manifest in the wake of a turn fin, that oscillation would have to be translated through the tub, and I would think the booms would absorb a frequency like that. I've seen this sort of thing in machining where a milling cutter is running too fast on a thin part not supported between clamping points. Usually, all you have to do is lay a finger on the part, acting as a dampener, and it will go away (except in more severe cases).

This looks like harmonics to me. The old lead crystal wine glass trick, anyone?

Anybody remember any of the discussions from days past on rudder cross sections? If you have a double taper (leading and trailing), a vibration will set in so severe, they've been known to destroy servos. This can also be seen in rudder cross sections where the wedge terminates short of the trailing edge, leaving a parallel condition, meaning no load from the termination of the wedge on back. This cavitation will actually cause a rapid pressure/vacuum oscillation. Since our turn fins have this condition of the wedge terminating before the trailing edge, is it possible that this is just the nature of the beast and we're just noticing it? When the turn fin is fully positively loaded in a turn, it may not happen. When the fin is at least partially loaded negatively in the straights (I think most of us toe them in some, countering prop walk), it probably wouldn't present itself, either. But in those brief instances where the overall cross-section is at a truly neutral state, this high frequency harmonics may onset for a short time. This may just be the first time anybody has caught the boat right at that magic moment with a fast enough aperture time for it to show up. Different materials, thickness, length, depth, shape, anchor location, wedge profile, including wedge termination condition (angle, rounded, feathered) etc... even rigidity of the booms would all factor in and make every boat unique.

Thoughts?

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[wayne middlemiss]

Guys, I think you would be on the money in summing it up

For the loading/unloading cycle of the prop to manifest in the wake of a turn fin, that oscillation would have to be translated through the tub, and I would think the booms would absorb a frequency like that. I've seen this sort of thing in machining where a milling cutter is running too fast on a thin part not supported between clamping points. Usually, all you have to do is lay a finger on the part, acting as a dampener, and it will go away (except in more severe cases).

This looks like harmonics to me. The old lead crystal wine glass trick, anyone?

Anybody remember any of the discussions from days past on rudder cross sections? If you have a double taper (leading and trailing), a vibration will set in so severe, they've been known to destroy servos. This can also be seen in rudder cross sections where the wedge terminates short of the trailing edge, leaving a parallel condition, meaning no load from the termination of the wedge on back. This cavitation will actually cause a rapid pressure/vacuum oscillation. Since our turn fins have this condition of the wedge terminating before the trailing edge, is it possible that this is just the nature of the beast and we're just noticing it? When the turn fin is fully positively loaded in a turn, it may not happen. When the fin is at least partially loaded negatively in the straights (I think most of us toe them in some, countering prop walk), it probably wouldn't present itself, either. But in those brief instances where the overall cross-section is at a truly neutral state, this high frequency harmonics may onset for a short time. This may just be the first time anybody has caught the boat right at that magic moment with a fast enough aperture time for it to show up. Different materials, thickness, length, depth, shape, anchor location, wedge profile, including wedge termination condition (angle, rounded, feathered) etc... even rigidity of the booms would all factor in and make every boat unique.

Thoughts?

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[Andy Brown]

Guys,

For the loading/unloading cycle of the prop to manifest in the wake of a turn fin, that oscillation would have to be translated through the tub, and I would think the booms would absorb a frequency like that. I've seen this sort of thing in machining where a milling cutter is running too fast on a thin part not supported between clamping points. Usually, all you have to do is lay a finger on the part, acting as a dampener, and it will go away (except in more severe cases).

This looks like harmonics to me. The old lead crystal wine glass trick, anyone?

Anybody remember any of the discussions from days past on rudder cross sections? If you have a double taper (leading and trailing), a vibration will set in so severe, they've been known to destroy servos. This can also be seen in rudder cross sections where the wedge terminates short of the trailing edge, leaving a parallel condition, meaning no load from the termination of the wedge on back. This cavitation will actually cause a rapid pressure/vacuum oscillation. Since our turn fins have this condition of the wedge terminating before the trailing edge, is it possible that this is just the nature of the beast and we're just noticing it? When the turn fin is fully positively loaded in a turn, it may not happen. When the fin is at least partially loaded negatively in the straights (I think most of us toe them in some, countering prop walk), it probably wouldn't present itself, either. But in those brief instances where the overall cross-section is at a truly neutral state, this high frequency harmonics may onset for a short time. This may just be the first time anybody has caught the boat right at that magic moment with a fast enough aperture time for it to show up. Different materials, thickness, length, depth, shape, anchor location, wedge profile, including wedge termination condition (angle, rounded, feathered) etc... even rigidity of the booms would all factor in and make every boat unique.

Thoughts?

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

Some good points Brad.

I wonder if Aron's 45 SGX fin is bone stock or is it polished or modified in any way? Maybe Aron could post a pic of it.

 

[Tom Foley]

If you look at Limited and Unlimited Hydro photos you can see some of this effect also .

 

[Brad Christy]

Andy, others,

Something I just thought of......... If the turn fin were in a "true neutral" condition, it wouldn't be throwing up that wall of water. That turn fin is definitely loaded. So much for that part of the theory.....

I'm still thinking the wedge cut on the leading edge is causing a oscillating cavitation zone behind the termination of that wedge. One would need to take a close look at that turn fin, particularly the leading edge angle, and compare it to others that don't seem to be doing it. Now I'm gonna have to get some HD pics of MY 40 boat in the midst of a turn........

I guess, at the end of the day, you just have to ask if you like the way the boat is turning and how much speed/efficiency would a vibration of that high of frequency really costs you.

Nice little can of worms you've opened up here, Ian..........

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[Aron Alleva]

Just now seeing this thread, I will post some pictures of my turn fin and boat tonight.

 

[ace]

fellas i think you are over thinking this ,I personally think its a straight line trying to do a curved radius , if you wanted to stop this simply make your turn fin curved lol an then see it happen when you try to drive the boat in a straight line , the boat is turning a perfect curve an is angling the straight line in perfect jumps ,pulses what ever you want to call it . draw a perfect curved radius an then get a straight line an try driving it around the curve what do you have to do to get it round , another thing to me is the side pressure is hitting that turn fin perfectly in the middle for that to happen my 2cents . Cheers Ace