Turn Fin Sharpening

[Troy Glass]

Just wondering if any one can tell me the reason for only sharpening the outside edge of hydro turn fins and not both sides?

 

[Tom Foley]

Basically to help "push " the boat left a bit to counteract drag of the fin on the right side of the hull . In general smaller fins such as on the Eagle etc want to have a faily "blunt " type of sharpening done to the front right side of the fin and larger fins such as the Roadrunner type seem to like a more gradual thinning of the fin . By sharpening both sides you will lose this " free " trimming effect and will have to toe in the right sponson more , or , gasp , use more left rudder correction (loss of speed ).

 

[thomaselkins]

Basically to help "push " the boat left a bit to counteract drag of the fin on the right side of the hull . In general smaller fins such as on the Eagle etc want to have a faily "blunt " type of sharpening done to the front right side of the fin and larger fins such as the Roadrunner type seem to like a more gradual thinning of the fin . By sharpening both sides you will lose this " free " trimming effect and will have to toe in the right sponson more , or , gasp , use more left rudder correction (loss of speed ).

Tom

Your so smart, someday I well be like that

 

[gooycheese]

I am under the impression that on riggers .... atleast the JAE type rigger you should sharpen both sides of the turnfin down to the bend then sharpen just the outside. I have mine sharpened on just the outside all the way (Its off my firefighter) and I have been told if I changed that to sharpened on both sides the boat will wanna not go right so bad and will naturally wanna track a little more left. I have not tried this yet, still using old fin but will be trying. I know that some of the Best JAE boats are using turnfin sharpened on both sides down to the bend.

 

[John Knight]

I am under the impression that on riggers .... atleast the JAE type rigger you should sharpen both sides of the turnfin down to the bend then sharpen just the outside. I have mine sharpened on just the outside all the way (Its off my firefighter) and I have been told if I changed that to sharpened on both sides the boat will wanna not go right so bad and will naturally wanna track a little more left. I have not tried this yet, still using old fin but will be trying. I know that some of the Best JAE boats are using turnfin sharpened on both sides down to the bend.

Paul,

Correct on the sharpening of the JAE fin - both sides. That does not work on the Roadrunners, Crapshooters, etc. The fin and boat is vastly different for the JAE than the others. Mine went straight when the fin was sharpened on both sides. Only testing will tell for you & others.

 

[Marty Davis]

Just wondering if any one can tell me the reason for only sharpening the outside edge of hydro turn fins and not both sides?

Troy:

In addition to the torque reason, if you will consider this:

When the boat is in the turn it is trying to slip sideways toward the outside. If you have a sharpened edge on the inside, it now becomes less than 90 degrees to the water and it will try to lift the turn fin because of this angle.

The same thing happens at the other end of the boat with the rudder. IF you don' have the leading edge at 90 degrees to the run attitude, the rudder blade will either lift or suck down the rear of the boat. Cats and monos use this effect to change the attitude of the rear of the boat in the turns.

With the turn fin, you do not want to sharpen the fin on the inside or have any sort of doubler either. Both will try to lift the turn fin out of the water. You want the inside of the fin as flat as possible.

 

[Ted buckley]

I am under the impression that on riggers .... atleast the JAE type rigger you should sharpen both sides of the turnfin down to the bend then sharpen just the outside. I have mine sharpened on just the outside all the way (Its off my firefighter) and I have been told if I changed that to sharpened on both sides the boat will wanna not go right so bad and will naturally wanna track a little more left. I have not tried this yet, still using old fin but will be trying. I know that some of the Best JAE boats are using turnfin sharpened on both sides down to the bend.

Paul,

Correct on the sharpening of the JAE fin - both sides. That does not work on the Roadrunners, Crapshooters, etc. The fin and boat is vastly different for the JAE than the others. Mine went straight when the fin was sharpened on both sides. Only testing will tell for you & others.

I seem to remember another Thread about this, and it also mentioned about cutting the top of the fin-off. I Cut-off the top portion of the JAE fin 1/4" down to the bottom of slots, Sharpened both sides down to the curved part, re-drilled new holes through the Blade and mounted. I gained 8mph and took a 1st and second last weekend with this set-up. Boat trimmed straight with less depth on the fin. Actually turned way better in the turns.

 

[gooycheese]

I know nothing about running a shorter fin, all the fins i see on the JAE boats are huge compared to the one on my boat.

 

[John Knight]

I am under the impression that on riggers .... atleast the JAE type rigger you should sharpen both sides of the turnfin down to the bend then sharpen just the outside. I have mine sharpened on just the outside all the way (Its off my firefighter) and I have been told if I changed that to sharpened on both sides the boat will wanna not go right so bad and will naturally wanna track a little more left. I have not tried this yet, still using old fin but will be trying. I know that some of the Best JAE boats are using turnfin sharpened on both sides down to the bend.

Paul,

Correct on the sharpening of the JAE fin - both sides. That does not work on the Roadrunners, Crapshooters, etc. The fin and boat is vastly different for the JAE than the others. Mine went straight when the fin was sharpened on both sides. Only testing will tell for you & others.

I seem to remember another Thread about this, and it also mentioned about cutting the top of the fin-off. I Cut-off the top portion of the JAE fin 1/4" down to the bottom of slots, Sharpened both sides down to the curved part, re-drilled new holes through the Blade and mounted. I gained 8mph and took a 1st and second last weekend with this set-up. Boat trimmed straight with less depth on the fin. Actually turned way better in the turns.

Ted,

The other thread noted that a doubler plate, using the original zipp kit fin cut off above the water line, as being used as a alternative. The intent is to brace the fin from bending. It is similar to using a brace on the Roadrunner, Crapshooter,etc., fins.

Nothing was noted about cutting off the kit fin height. However, that is a real possibility. Again testing will only tell.

 

[Ted buckley]

I know nothing about running a shorter fin, all the fins i see on the JAE boats are huge compared to the one on my boat.

Paul, I can't remember the thread, but it talked about cutting-off the top portion of the fin. My fin was huge - too, but I cut the top slots off of it - re-drilled new holes and noticed a remarkable difference in speed and handling - this weekend. My Son, was even impressed. My Hydro is a cross between a JAE & Kepps. I didn't copy any of the plans on either - but got the general design. The hardware(Fin) on the hull is a JAE fin. The strut is Speed master & the Rudder is from JAE. I won't recommend to anybody to just go and cut-off hteir fin - due to handeling in the corners, but for some that want to experiment - they might gain some speed without compromising handeling.

 

[Ted buckley]

I am under the impression that on riggers .... atleast the JAE type rigger you should sharpen both sides of the turnfin down to the bend then sharpen just the outside. I have mine sharpened on just the outside all the way (Its off my firefighter) and I have been told if I changed that to sharpened on both sides the boat will wanna not go right so bad and will naturally wanna track a little more left. I have not tried this yet, still using old fin but will be trying. I know that some of the Best JAE boats are using turnfin sharpened on both sides down to the bend.

Paul,

Correct on the sharpening of the JAE fin - both sides. That does not work on the Roadrunners, Crapshooters, etc. The fin and boat is vastly different for the JAE than the others. Mine went straight when the fin was sharpened on both sides. Only testing will tell for you & others.

I seem to remember another Thread about this, and it also mentioned about cutting the top of the fin-off. I Cut-off the top portion of the JAE fin 1/4" down to the bottom of slots, Sharpened both sides down to the curved part, re-drilled new holes through the Blade and mounted. I gained 8mph and took a 1st and second last weekend with this set-up. Boat trimmed straight with less depth on the fin. Actually turned way better in the turns.

Ted,

The other thread noted that a doubler plate, using the original zipp kit fin cut off above the water line, as being used as a alternative. The intent is to brace the fin from bending. It is similar to using a brace on the Roadrunner, Crapshooter,etc., fins.

Nothing was noted about cutting off the kit fin height. However, that is a real possibility. Again testing will only tell.

Thanks John, Now I remember the thread.