turn fins on tub

[TomMoorehouse]

I'm always thinking about rigger design. One thing that could help me with my current ideas would be to have the turn fin on the tub not the sponson. I know it has been done before. What are the problems associated with it. Any reason not to do it??? Will the fin still have a curve to it??

Plaease share your thoughts/experiences

Thanks

Tom

 

[John Kubitz]

Tom, Think about the turn fin being a pivot point. Also what is going to happen to the tub when the water comes up from the turn fin esp if it has a hook.

 

[TomMoorehouse]

It either needs a spacer so the water won't ride up and lift the tub or have it on the left side I suppose. ??

 

[Norm Doerr]

As noted above. The turnfin is a pivot. Also there is leverage out there on the sponson. I am no expert, but I would assume the first issue would be increasing servo power to turn the boat, (because the pivot point is now closer to the middle of the boat). The best turnfin guy I know usually describes it as running up to a pole and grabbing it to swing around and change direction, as seen on numerous playgrounds throughout the world.

 

[John Kubitz]

It either needs a spacer so the water won't ride up and lift the tub or have it on the left side I suppose. ??

The spacer is the distance from the tub to the sponson. Putting it on the left side will cause the right sponson to lift. (slow day @ work)?

 

[Charles Perdue]

Hello Tom, originally the Octura Wing Ding came with the turn fin mounted between the right sponson bracket and the hull. This only turned so-so. Moved the turn fin out to the inside of the right sponson and there was a very large improvement in the turning ability. Moved the turn farther out and back on the right sponson,angled the turn fin in at the bottom 18 degrees and the rest is history. Domination until everyone else caught up.

Charles

 

[JoeWScott]

I have wondered if extending the inside sponson sheeting past the sponson bottom would act as turn fin. Was thinking this may work on a s.a.w application. Has anyone tried this?

 

[John Kubitz]

I have wondered if extending the inside sponson sheeting past the sponson bottom would act as turn fin. Was thinking this may work on a s.a.w application. Has anyone tried this?

It might work for a real gentle turn turn @ low speed, but it will not be strong enough to work @ high speed unless it was very thick. Then it would create excessive drag slowing you down. .032 aluminum will bend because it is not strong enough. I use .032 spring stainless steel formed with a 20 ton hydraulic press.

 

[Marty Davis]

So to get everyone thinking, why not have a turn fin on each sponson?

 

[Hydro Junkie]

I've seen this asked several times in the scale forum, though more so for left hand turning, but always with the same answer. Putting a turn fin on the left side of the boat would do two things:

1) roll the boat since it would grab any time the right fin unhooked and put all that pressure on the outside during the turns with nothing to stabilize the boat further out to the left

2) increase drag on the left side of the boat and increase straight line stability, requiring a heavier servo on the rudder to turn the boat. This was demonstrated back in 1974 with the U-95. It was extremely hard to get that boat to turn with three vertical tails at the transom. After it sank on Lake Washington during the Seafair Race, it was raised and rebuilt to run a piston engine with only one centerline vertical tail. The turning issue vanished with the two outboard tails, so that has to say something

 

[Bill Gibson]

So to get everyone thinking, why not have a turn fin on each sponson?

I wonder how much drag is acceptable?? Guess it would be maybe a cutnhackntry thing....Ken Warby went 317 mph many years ago by just torching a couple of inches off the bottom of the rudder...on a full size boat. interesting!

 

[Norm Doerr]

So to get everyone thinking, why not have a turn fin on each sponson?

I wonder how much drag is acceptable?? Guess it would be maybe a cutnhackntry thing....Ken Warby went 317 mph many years ago by just torching a couple of inches off the bottom of the rudder...on a full size boat. interesting!

This is going to get interesting, (I hope), I have no clue BUT I would think that they would have to be two different fins, and not as big as running one. I have to sleep on this one..

 

[Chris Wood]

So to get everyone thinking, why not have a turn fin on each sponson?

marty i know how you like to FISH for answer's so mine is..

a. i would think they would fight each other in the corner.

b. i would think it would be hard to keep the boat tracking straight.

chris

 

[TomMoorehouse]

So to get everyone thinking, why not have a turn fin on each sponson?

marty i know how you like to FISH for answer's so mine is..

a. i would think they would fight each other in the corner.

b. i would think it would be hard to keep the boat tracking straight.

chris

would it make the boat trip in the turn??

 

[Jeff Lutz]

So to get everyone thinking, why not have a turn fin on each sponson?

I'm not sure what you want people to think of on that one..... But,its obvious hardly anybody on this thread really knows what makes a turnfin work. Currently, everyone running outriggers are using 'Pressing Down turn fins'.But,They don't know why. (Remember from school-"With every action there is a equal and opposite reaction".The rear rake on a turn fin slanting forward makes water break over the top,making it a 'Pressing down' fin.This pulls the right sponson down helping the pivot point and countering the force towards the left sponson when you throw the boat in the turn. If you reverse this rake direction on the back side of the turn fin,water would then break under the bottom of the fin lifting the sponson.(Pinckerts Gators had that style). Mounting the fin on the hull (Right side) would lessen the effect of pulling down the right sponson-which would not be good. Mounting the current style turn fin on the left side of the hull would try to snap roll the boat.The fin is mounted on the right sponson for right turns for good reasons. Jeff Lutz

 

[Marty Davis]

So to get everyone thinking, why not have a turn fin on each sponson?

I'm not sure what you want people to think of on that one..... But,its obvious hardly anybody on this thread really knows what makes a turnfin work. Currently, everyone running outriggers are using 'Pressing Down turn fins'.But,They don't know why. (Remember from school-"With every action there is a equal and opposite reaction".The rear rake on a turn fin slanting forward makes water break over the top,making it a 'Pressing down' fin.This pulls the right sponson down helping the pivot point and countering the force towards the left sponson when you throw the boat in the turn. If you reverse this rake direction on the back side of the turn fin,water would then break under the bottom of the fin lifting the sponson.(Pinckerts Gators had that style). Mounting the fin on the hull (Right side) would lessen the effect of pulling down the right sponson-which would not be good. Mounting the current style turn fin on the left side of the hull would try to snap roll the boat.The fin is mounted on the right sponson for right turns for good reasons. Jeff Lutz

Jeff:

So, what would happen with a small turn fin on each sponson? Would you then have a really quick pivot activated by the rudder? Would the turn fins (center of pressure) have to be near the Hulls dynamic center of pressure? So, with the fins behind the sponson, there would not be a lifting effect because of water not being able to release upward? Thus no negative effect of the fin on the left side? Would the fins on each side keep the boat solid in the turns with the rudder being the activator?

 

[Jeff Lutz]

So to get everyone thinking, why not have a turn fin on each sponson?

I'm not sure what you want people to think of on that one..... But,its obvious hardly anybody on this thread really knows what makes a turnfin work. Currently, everyone running outriggers are using 'Pressing Down turn fins'.But,They don't know why. (Remember from school-"With every action there is a equal and opposite reaction".The rear rake on a turn fin slanting forward makes water break over the top,making it a 'Pressing down' fin.This pulls the right sponson down helping the pivot point and countering the force towards the left sponson when you throw the boat in the turn. If you reverse this rake direction on the back side of the turn fin,water would then break under the bottom of the fin lifting the sponson.(Pinckerts Gators had that style). Mounting the fin on the hull (Right side) would lessen the effect of pulling down the right sponson-which would not be good. Mounting the current style turn fin on the left side of the hull would try to snap roll the boat.The fin is mounted on the right sponson for right turns for good reasons. Jeff Lutz

Jeff:

So, what would happen with a small turn fin on each sponson? Would you then have a really quick pivot activated by the rudder? Would the turn fins (center of pressure) have to be near the Hulls dynamic center of pressure? So, with the fins behind the sponson, there would not be a lifting effect because of water not being able to release upward? Thus no negative effect of the fin on the left side? Would the fins on each side keep the boat solid in the turns with the rudder being the activator?

Marty, If you add a turn fin to the left sponson designed like the ones you are running now- THE BOAT WILL SNAP ROLL. (If your still running fast enough). Water would break off the top of the back rack of the fin and stick the left sponson badly.The reaction off the right would not have a chance to counter.The left would get the most water first and win the battle. Now, if you put a 'lifting fin' on the left and keep a 'press down' fin on the right the boat would turn,but,not as well.I never said anything about fins behind the sponson,so I'm not sure what you are talking about. If you mean the turn fin mounted behind the planing surface,not even with the side,that does not matter,either way the back rack of the fin ,once the boat turns sideways, would take control and water would still be able to come of the fin. P.s. This is not a debate,I'm stating the facts.

 

[Charles Perdue]

Martys fishing again!

A turn fin on both sponsons with a small fin on the left and a large fin on the right sponson WILL snap roll, not just theory, tried many combinations years ago. Will not work.

The correct turn fin on the right sponson does not have to pull the right sponson down to make it work. The correct fin holds the sponson in the same position as in the straight -a- way. The boat just does a slow pivot around it. When it is right, the boat "Sweeps" the turns, loosing very little speed. The correct shape doesn't have to be a "Hooked" or a curved turn fin either.

While we are playing with different ideas, what about WHEELS on the sponsons. Don't laugh, they work great in the straights and so-so in the turns. They are just a bear to get up on plane.

Charles

 

[M@MRacing]

Marty is sitting back laughing

 

[John Kubitz]

Marty is sitting back laughing

If anyone remembers the Prather O.B. Tunnel boats with the turn fins you know that if you thought about making a left turn at speed they would roll over.