Turn Fins

[PHM Racing]

Hi, Mike! I'm glad to read your article! Resourch instead guessing! Thanks. Boris

I think that one might have been directed at me.

If you worked on turn fins every day for the next year, you still wouldn't have done as much resourch as I have on turn fins.

I just want to be helpful to everyone and pass along those tidbits that have helped me figure out how and why turn fins work.

No i think it was for me Marty , on the info i posted

 

[El Zorro]

While the information Mike has posted in a previous post can be helpful to some but more confusing to others, I strongly suggest that anyone looking to improve the performance of any of their model boats do the same as John Finch, Marty Davis, Mark Grannis and some others that have posted on this subject have been doing for many, MANY years; GO TO THE LAKE AND TEST.TEST AND TEST SOME MORE!!! I can promise you that these people have forgotten about more things to do to a boat than many of us will even think about trying. If you have ever been around any of these guys when they are at the lake testing you will know why they have multiple World Records, US-1 titles and more championships than the law allows. There is no one change that you will make to a boat to make it run 10 MPH faster ( not usually ) or make it go around the corners as fast, either. It is always a combination of things in the set-up of the boat. These guys share a lot of their hard work and information on boards like this one and I find it hard to believe that there are those out there that would question or dispute their knowledge. What works for me may not work the same for you. But I'm not going to tell you that your way is wrong. Give these guys some credit for sharing their years of knowledge with those of us who might not have a lot of time to spend at the lake.

Turn fins are not quite the same as airplane wings. The shape of the fin, how the leading edge is cut, weather a fin is "airfoiled" shaped, how much and where a fin is cupped all make a difference in how a turn fin reacts on a particular hydroplane. If you listen to what some of these experienced boaters are saying in threads like this one and some of the previous threads a while back it should give you some ideas to make up some different turn fins to go out and try on your boat. Spend some time at the lake and try different things. You usually find 5 things that DON'T work and one thing that does................

Dick Tyndall

 

[Joe Warren]

While the information Mike has posted in a previous post can be helpful to some but more confusing to others, I strongly suggest that anyone looking to improve the performance of any of their model boats do the same as John Finch, Marty Davis, Mark Grannis and some others that have posted on this subject have been doing for many, MANY years; GO TO THE LAKE AND TEST.TEST AND TEST SOME MORE!!! I can promise you that these people have forgotten about more things to do to a boat than many of us will even think about trying. If you have ever been around any of these guys when they are at the lake testing you will know why they have multiple World Records, US-1 titles and more championships than the law allows. There is no one change that you will make to a boat to make it run 10 MPH faster ( not usually ) or make it go around the corners as fast, either. It is always a combination of things in the set-up of the boat. These guys share a lot of their hard work and information on boards like this one and I find it hard to believe that there are those out there that would question or dispute their knowledge. What works for me may not work the same for you. But I'm not going to tell you that your way is wrong. Give these guys some credit for sharing their years of knowledge with those of us who might not have a lot of time to spend at the lake.Turn fins are not quite the same as airplane wings. The shape of the fin, how the leading edge is cut, weather a fin is "airfoiled" shaped, how much and where a fin is cupped all make a difference in how a turn fin reacts on a particular hydroplane. If you listen to what some of these experienced boaters are saying in threads like this one and some of the previous threads a while back it should give you some ideas to make up some different turn fins to go out and try on your boat. Spend so time at the lake and try some different things. You usually find 5 things that DON'T work and one thing that does................

Dick Tyndall

I agree with Dick, Those that are @ the lake testing will be Ready Come Race day! The rest will still be talking about it... Marty is a Prop Wizard. Now he is working overtime testing Turn fins & Boat balance. Each of us have our own thing. Some are into Engines, Some props, Some boat set up, It takes it all to have a Exceptional boat on Race day! B)

 

[PHM Racing]

While the information Mike has posted in a previous post can be helpful to some but more confusing to others, I strongly suggest that anyone looking to improve the performance of any of their model boats do the same as John Finch, Marty Davis, Mark Grannis and some others that have posted on this subject have been doing for many, MANY years; GO TO THE LAKE AND TEST.TEST AND TEST SOME MORE!!! I can promise you that these people have forgotten about more things to do to a boat than many of us will even think about trying. If you have ever been around any of these guys when they are at the lake testing you will know why they have multiple World Records, US-1 titles and more championships than the law allows. There is no one change that you will make to a boat to make it run 10 MPH faster ( not usually ) or make it go around the corners as fast, either. It is always a combination of things in the set-up of the boat. These guys share a lot of their hard work and information on boards like this one and I find it hard to believe that there are those out there that would question or dispute their knowledge. What works for me may not work the same for you. But I'm not going to tell you that your way is wrong. Give these guys some credit for sharing their years of knowledge with those of us who might not have a lot of time to spend at the lake.Turn fins are not quite the same as airplane wings. The shape of the fin, how the leading edge is cut, weather a fin is "airfoiled" shaped, how much and where a fin is cupped all make a difference in how a turn fin reacts on a particular hydroplane. If you listen to what some of these experienced boaters are saying in threads like this one and some of the previous threads a while back it should give you some ideas to make up some different turn fins to go out and try on your boat. Spend so time at the lake and try some different things. You usually find 5 things that DON'T work and one thing that does................

Dick Tyndall

I agree with Dick, Those that are @ the lake testing will be Ready Come Race day! The rest will still be talking about it... Marty is a Prop Wizard. Now he is working overtime testing Turn fins & Boat balance. Each of us have our own thing. Some are into Engines, Some props, Some boat set up, It takes it all to have a Exceptional boat on Race day! B)

You guy's are dead on , lots of testing , i posted the previous post just for some info , some can be used and maybe helpfull , the only reason i posted it is just for info , i'm just a hick from Canuck EH

Keep this thred going with good info , i will be testing a new designed turning device this summer , not sure if it will work , but i guess that why it's called test test test and test agian.

Happy testing

 

[Marty Davis]

While the information Mike has posted in a previous post can be helpful to some but more confusing to others, I strongly suggest that anyone looking to improve the performance of any of their model boats do the same as John Finch, Marty Davis, Mark Grannis and some others that have posted on this subject have been doing for many, MANY years; GO TO THE LAKE AND TEST.TEST AND TEST SOME MORE!!! I can promise you that these people have forgotten about more things to do to a boat than many of us will even think about trying. If you have ever been around any of these guys when they are at the lake testing you will know why they have multiple World Records, US-1 titles and more championships than the law allows. There is no one change that you will make to a boat to make it run 10 MPH faster ( not usually ) or make it go around the corners as fast, either. It is always a combination of things in the set-up of the boat. These guys share a lot of their hard work and information on boards like this one and I find it hard to believe that there are those out there that would question or dispute their knowledge. What works for me may not work the same for you. But I'm not going to tell you that your way is wrong. Give these guys some credit for sharing their years of knowledge with those of us who might not have a lot of time to spend at the lake.Turn fins are not quite the same as airplane wings. The shape of the fin, how the leading edge is cut, weather a fin is "airfoiled" shaped, how much and where a fin is cupped all make a difference in how a turn fin reacts on a particular hydroplane. If you listen to what some of these experienced boaters are saying in threads like this one and some of the previous threads a while back it should give you some ideas to make up some different turn fins to go out and try on your boat. Spend some time at the lake and try different things. You usually find 5 things that DON'T work and one thing that does................

Dick Tyndall

Well said Dick....

AWe sure don't want to forget Andy Brown in your comments. Might be difficult sometimes to get him to chime in, but Andy REALLY understands what makes an outrigger tick.

Many others too.....

 

[Bill Gibson]

I have a boat that Marty made me a turn fin for.....Ive never had a better turning boat ........EVER! And knowing Mr. Davis as i do...he would come up with a way to make it even better! When Marty so much as opens his mouth, i tend to listen VERY intently!

 

[tnrcboatracer]

That was the long explanation for flow pressure differential. It is generally simplified to the familiar Bernoulli equation. In the case of wings, the air is stationary, and the wing moves. Due to friction there is a difference in upper and lower surface velocity, but there is also turbulent flow, and vortex generation, too. Add to that transonic shock waves in the case of high speed flight, and you have a huge can of worms. Bernoulli is actually a 29 dimensional nonlinear partial differential equation; it is grossly simplified to P1= P0 + 1/2 RhoV2. The part about circulation and vortex shedding was interesting. Circulation is a fact, and if you put a horizontal cylindrical basket over a bicycle and rotate it while moving forward, you will take off. It also explains why a baseball can be made to curve. ANd vortex shedding is the cause of the Tacoma Narrows bridge collapse. Well, vortex shedding the the structure's natural frequency. Anyhow, interesting read.

 

[Brad Christy]

Guys,

All this discussion about wings is very interesting, but completely off base, as we are not talking about a wing, we are talking about a stationary RUDDER. It's not about lift, it's about direction. If a turnfin is generating lift, either horizontally or vertically, it is doing more than it is intended to do and is consuming energy to do so, which is scrubbing speed. If the bernoulli principal is involved in any way, this is also scrubbing speed. You can do whatever you want with the length, depth, thickness, shape, curl, hook, angle, whatever........ The leading edge should be sharp, with as gradual of a parting of the water as possible, and the trailing edge as square as possible with the sharpest edges possible. All other properties will obviously have an affect on how well the boat turns, but when you get done shaping and bending, always get a turnfin back to a condition of gradual lead-in, square exit and sharp edges everywhere it gets wet.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

 

[Mark Grannis]

Dick, your very kind for mentioning my name with John and Marty, but I'm no where near their level of expertise. Marty & Ralph assist me with my boat setups. Chad & I are lucky to have them in our corner.

The only reason I started asking about turn fins was to get ideas, so I could learn on some local gas sport hydros.

I thank everyone for their input & ideas. I do have to admit the extremely technical post accelerated my reading narcoleptic condition.

MG

 

[tnrcboatracer]

Guys,
All this discussion about wings is very interesting, but completely off base, as we are not talking about a wing, we are talking about a stationary RUDDER. It's not about lift, it's about direction. If a turnfin is generating lift, either horizontally or vertically, it is doing more than it is intended to do and is consuming energy to do so, which is scrubbing speed. If the bernoulli principal is involved in any way, this is also scrubbing speed. You can do whatever you want with the length, depth, thickness, shape, curl, hook, angle, whatever........ The leading edge should be sharp, with as gradual of a parting of the water as possible, and the trailing edge as square as possible with the sharpest edges possible. All other properties will obviously have an affect on how well the boat turns, but when you get done shaping and bending, always get a turnfin back to a condition of gradual lead-in, square exit and sharp edges everywhere it gets wet.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Like it or not, if a fluid is flowing (or more correctly, an object is moving through a fluid), Bernoulli is involved. That equation (set of equations) is (are) THE defining physical properties of fluid flow. The square corners at the back and the front edge break ventilate the flow. Air bubbles in the fluid flowing along the surface reduce the friction. The bubbles change the properties of the fluid, and the separated (ventilated) flow has less drag. The resisting force of the fin or rudder is 'lift'; if not, the fin would not resist, and the boat would skid sideways.

But this is all semantics. Bernoulli is far too complex to apply without a Cray supercomputer to analyze all the variables. Just remember, a symetrical wing (straight chord line) at 0 angle of attack has no 'lift'. The same for a turn fin. The angle of attack on the fin occurs when the boat turns. Same with the rudder. And filing the edge on only one side makes the fin asymetrical, so it has a slight amount of 'lift' (assuming the flow stays attached). I suspect the momentum thrust on the leading edge is greater than the lift due to the flow separation at the break on the outboard edge. Hence Andy's recommendation to leave the edge on the CMDI fins alone.

In closing, all of this has a foundation in fluid dynamics. But it is far to complex to get a clear cuase and effect relationship. As Mr. Finch stated, it is best to just go out and test. See what works, and then see if you can make it better. Everything will have an effect on everything else. What works on my setup may not work on yours. But it isn't magic, either. There is science behind it. Just that the science is actually very complex; so complex, that you can easily get lost and a small detail will completely change the result.

 

[Chris Wood]

Mark,

One thing to play with if you are making a fin with a hook and not bend lines. is the dia of the hook .. I messed and messed and messed and messed with mine.. once i got it.. i then started on the shape. i found a good GRADUAL shape that flows from the top of the fin to the leading edge on the bottom.. my old fins we much more abrupt and caused a few issue's i didn't like.. that has since been corrected and things are much happier.

if you want give me a call sometime i would like to speak with you anyway.

chris wood

319-750-0893

 

[Marty Davis]

Guys,
All this discussion about wings is very interesting, but completely off base, as we are not talking about a wing, we are talking about a stationary RUDDER. It's not about lift, it's about direction. If a turnfin is generating lift, either horizontally or vertically, it is doing more than it is intended to do and is consuming energy to do so, which is scrubbing speed. If the bernoulli principal is involved in any way, this is also scrubbing speed. You can do whatever you want with the length, depth, thickness, shape, curl, hook, angle, whatever........ The leading edge should be sharp, with as gradual of a parting of the water as possible, and the trailing edge as square as possible with the sharpest edges possible. All other properties will obviously have an affect on how well the boat turns, but when you get done shaping and bending, always get a turnfin back to a condition of gradual lead-in, square exit and sharp edges everywhere it gets wet.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Like it or not, if a fluid is flowing (or more correctly, an object is moving through a fluid), Bernoulli is involved. That equation (set of equations) is (are) THE defining physical properties of fluid flow. The square corners at the back and the front edge break ventilate the flow. Air bubbles in the fluid flowing along the surface reduce the friction. The bubbles change the properties of the fluid, and the separated (ventilated) flow has less drag. The resisting force of the fin or rudder is 'lift'; if not, the fin would not resist, and the boat would skid sideways.

But this is all semantics. Bernoulli is far too complex to apply without a Cray supercomputer to analyze all the variables. Just remember, a symetrical wing (straight chord line) at 0 angle of attack has no 'lift'. The same for a turn fin. The angle of attack on the fin occurs when the boat turns. Same with the rudder. And filing the edge on only one side makes the fin asymetrical, so it has a slight amount of 'lift' (assuming the flow stays attached). I suspect the momentum thrust on the leading edge is greater than the lift due to the flow separation at the break on the outboard edge. Hence Andy's recommendation to leave the edge on the CMDI fins alone.

In closing, all of this has a foundation in fluid dynamics. But it is far to complex to get a clear cuase and effect relationship. As Mr. Finch stated, it is best to just go out and test. See what works, and then see if you can make it better. Everything will have an effect on everything else. What works on my setup may not work on yours. But it isn't magic, either. There is science behind it. Just that the science is actually very complex; so complex, that you can easily get lost and a small detail will completely change the result.

Jon:

You are correct about your final analysis.

As is the case so many times in our hobby, the amount of variables are great enough that it is difficult to assign a result directly to one change. You must be very careful to try something without changing ANYTHING else so that you see the effect. Also something that Len Skwiera ( an IMPBA HAll of Fame Member) told me when I started boating: AWhen you make a change make a BIG CHANGE so that you can see the effect. Then go somewhere in between when you have seen the effect and found it beneficial. As a comparison, Ed Hughey also an IMPBA HAll of Fame Member and my Mentor when I started could not do this. He ALWAYS made tiny changes and could not easily see the effect. It kept him from advancing quickly while Len was advancing very quickly.

With turn fins, this works especially well. You can see big changes and you will learn quickly the way that various components and configurations contribute to the advancing progress.

This is a tip that I hope you will use. I will serve you well.

 

[PHM Racing]

Guys,
All this discussion about wings is very interesting, but completely off base, as we are not talking about a wing, we are talking about a stationary RUDDER. It's not about lift, it's about direction. If a turnfin is generating lift, either horizontally or vertically, it is doing more than it is intended to do and is consuming energy to do so, which is scrubbing speed. If the bernoulli principal is involved in any way, this is also scrubbing speed. You can do whatever you want with the length, depth, thickness, shape, curl, hook, angle, whatever........ The leading edge should be sharp, with as gradual of a parting of the water as possible, and the trailing edge as square as possible with the sharpest edges possible. All other properties will obviously have an affect on how well the boat turns, but when you get done shaping and bending, always get a turnfin back to a condition of gradual lead-in, square exit and sharp edges everywhere it gets wet.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Ya you guy's are rite , so i edited the long post , sorry about that , didn't mean to go off coarse , my bad

 

[Mike Larson]

Learning..... leeeeaaarning........ thanks men..... the reading is great....... and much appreciated.....

Dick are you feeling well enough to manufacture fins again?.... ( my boats have them on them, and a couple to file and test may come about)....

please keep goin' on good topics..... the possibilities are endless.... Mike