Scale Turn fins

[Glenn 787]

Glen

Do you have any tork weight up in the left sponson? All sport boats need the weight to keep it on a even keel. I would guess you would need 10-12 oz or so. Depending on the weight of the boat. Since you said you changed the prop and are getting more speed out of it, this amplifies that you don't have enough weight in the left sponson.

Mike

I recently bought a Sport 21 rtr so I'd have a Sunday boat to start the year until I got mine built. First thing I did was rip out all the lead inside the sponsons......came out to 10-12 oz. I hope I don't need to load it back up.

Was supposed to be a good running boat but I just can't help changing things.

Day 1: I picked up the boat and was happy I had something ready to run for Sundays.

Day 2: The front of the sponsons are ripped apart trying to get out all the lead and brass tubes holding them.

Day 3: Start cutting up and changing the running surfaces and rip out the stuffing box.

Day 4: Strip the old paint.

Occasionally glance over at it the next few weeks.

First race is a little over 3 weeks away and I don't have a Sunday boat ready :huh:

 

[Mike Hughes]

I am confused. We are talking a scale boat right? If it is a curl fin, then set up is critical. If not right it will make the ride ugly. 10-12 oz sounds a bit much for a sp 20. I think I added 1.5 oz for my sp 20 in the left sponson. I have 8 oz in the the left sponson of my Mutt2.

Mike

 

[Glenn 787]

I am confused. We are talking a scale boat right? If it is a curl fin, then set up is critical. If not right it will make the ride ugly. 10-12 oz sounds a bit much for a sp 20. I think I added 1.5 oz for my sp 20 in the left sponson. I have 8 oz in the the left sponson of my Mutt2.

Mike

Yeah, I didn't think my scale needed any weight added since the problem didn't start until after the fin change. I'm going to make some adjustments and changes with the fins I have and Dick is sending a different one to try.

When you mentioned sport boats I went and changed the subject on you.

 

[Don Ferrette]

I am confused. We are talking a scale boat right? If it is a curl fin, then set up is critical. If not right it will make the ride ugly. 10-12 oz sounds a bit much for a sp 20. I think I added 1.5 oz for my sp 20 in the left sponson. I have 8 oz in the the left sponson of my Mutt2.

Mike

Yeah, I didn't think my scale needed any weight added since the problem didn't start until after the fin change. I'm going to make some adjustments and changes with the fins I have and Dick is sending a different one to try.

When you mentioned sport boats I went and changed the subject on you.

Gotta really go with Mike on this one. A curved turn fin on a scale will hook up great in the turns but requires meticulous set up. Often you will find the best way is once you are absolutely sure it is perfectly parallel to the bottom running surfaces that you bolt it on & play with very minute changes in how the curve is to the boats actual running attitude. In other words slight rotation of the fin to alter the curve angle up or down, like Al suggested earlier. Often just because it looks right on the set up board doesn't mean that is how it will be when it is running on the water. I find this to be true more often on scale boats more than any other. Also looking at the pics of your boat, the rear of the sponson & from what I can tell the turn fin placement is rather far back than a typical set up which will make the boat hypersensitive to even a minor error. I can tell you that not every scale hull will work with a curved fin either & not blow off with a left trim. John Finch has a round nose Miss Bardahl that he won the Internats with 2 years in a row that goes around corners like it's on a rail. It has a curved fin & if you even touch left it leaves the water in a snap. Every boat is different, my Winston Eagle lobster hull had a Tyndall curved fin on it, went around corners like a rigger & you could correct left no problem. It actually turned too good, if you cranked it too hard you'd go inside of bouy #3. The up side to that is that I broke the 1/4 mile oval record with it because it could make those tight a$$ turns on the 1/4 mile course. But that boat is longer than most & has a fairly wide track or footpint. Now I didn't like the curved fin on my Smokin' Joe's, went back to a straight fin with a 7 degree angle in it. Your boat seems to have a narrow track & very short afterplane which will make it super sensitive to fin settings. The biggest thing is make your changes in very small movements, one at a time & document eveything. If doesn't work, make a change. You might spend a good number of trips to the pond to get it right or find out a particular fin just won't work. Like I said, every boat is is different when it comes to scales.

 

[Mike Hughes]

Scale boat is a sport boat just prettier. A curved fin is like a hydro foil when on the boat. For that matter, a straight fin is too. Just less of it. When the turn fin is pull back from parallel to the ride it will pull the right sponson down. This in turn will make any left turns lift the left sponson. If it is pushed forward it will lift the right sponson. If your boat does not maintain a steady boat ride around the course (like round noses tend to do) then this will change the angle as you go which equals kinda of a porpoising affect. It is all about tuning the fin to the ride. My sport boats that I build usually don't devieate very far from the curve being parallel to the ride. When I mount my fins, I make sure that I have a adjustable support attached to the back end of the mount. This way you can trim the fin to the center line of the boat. Most people don't do this. That little piece of angle alum. and the back of the sponson can't hold up to the G's we put on the fin in the corners. There is always some flexing. This will change the fin and affect the ride.

Mike

 

[Don Ferrette]

"My sport boats that I build usually don't deviate very far from the curve being parallel to the ride."

That is THE key sentence right there, Mike just found an easier way to say it than me.

Parallel to the ride as in when it's running, that is what I was getting at.

 

[Wesleys Custom RC]

While everybodys on the subject I have a question. How do you check a Tyndall trun fin?? He sharpens both sides where there is no straight side to check. Do you just kind of guess?? I've never asked Dick. I'm always too busy telling him how much I like his stuff.

 

[P THOMAS]

While everybodys on the subject I have a question. How do you check a Tyndall trun fin?? He sharpens both sides where there is no straight side to check. Do you just kind of guess?? I've never asked Dick. I'm always too busy telling him how much I like his stuff.

Im sure the inside surface is flat on the Tyndall fins the outside has the taper.

You can use a straight edge or ruler. Place the ruler on the inside of the fin extending to the front, the fin should align with the running pads edge, you may draw a parallel line on the pad to see this alignment.

If the fin is straight it should work ok.

With the fin tweaked out at the rear the boat will be senstive to left turns, You may find that if you tweak the fin in at the rear a bit, (more than straight) the boat will tolerate left corrections better.

With the fin straight and at the best angle the right sponson should not be sucked down or lifted by the fin.

PHIL T

 

[Wesleys Custom RC]

While everybodys on the subject I have a question. How do you check a Tyndall trun fin?? He sharpens both sides where there is no straight side to check. Do you just kind of guess?? I've never asked Dick. I'm always too busy telling him how much I like his stuff.

You can use a straight edge or ruler. Place the ruler on the inside of the fin extending to the front, the fin should align with the running pads edge, you may draw a parallel line on the pad to see this alignment.

If the fin is straight it should work ok.

With the fin tweaked out at the rear the boat will be senstive to left turns, You may find that if you tweak the fin in at the rear a bit, (more than straight) the boat will tolerate left corrections better.

With the fin straight and at the best angle the right sponson should not be sucked down or lifted by the fin.

PHIL T

Hay Phil, Waaaazzzzup?

My problem is that there is no "straight" or flat place on the inside or outside. I have a 5' straight edge but it "rocks" back and forth. It' like he did too god of a job polishing it. I wish it was still straight on one side.

I LOVE your boat by the way! Was that your boat that won the Winternats? Ken just traded for one!!! We got to help him sell it before he puts it together!!!!!! He's been helping me with mine and knows ALL my secrets!!

 

[El Zorro]

When making the turn fins I always polish the "money side" ( inside ) of the fin with a 4 1/2" angle grinder with a scotch brite pad attached. This removes any scratches in the fin and gives this side an overall finish. It's no secret that I don't like highly polished surfaces that have to go through water! Westley's fin probably had a deep scratch somewhere on the upper part of the fin and when it was buffed out, the surface was not completely flat. Normally the fin will be flat on this side from where the bend starts to the top of the fin. However, the side of the fin that mounts to the bracket is only buffed with a fine scotch brite wheel and should be pretty much flat.

Everything that Don and Phil have touched on here seems to be gospel for tuning the turn fin to the boat. Not all fins work on every kind of boat. I try to be flexible...........give me some ideas and send me a pattern. I try to work with my customers because I appreciate their business.

Dick

 

[El Zorro]

When making the turn fins I always polish the "money side" ( inside ) of the fin with a 4 1/2" angle grinder with a scotch brite pad attached. This removes any scratches in the fin and gives this side an overall finish. It's no secret that I don't like highly polished surfaces that have to go through water! Westley's fin probably had a deep scratch somewhere on the upper part of the fin and when it was buffed out, the surface was not completely flat. Normally the fin will be flat on this side from where the bend starts to the top of the fin. However, the side of the fin that mounts to the bracket is only buffed with a fine scotch brite wheel and should be pretty much flat.

Everything that Don and Phil have touched on here seems to be gospel for tuning the turn fin to the boat. Not all fins work on every kind of boat. I try to be flexible...........give me some ideas and send me a pattern. I try to work with my customers because I appreciate their business.

Dick

Didn't mean to leave Mike Hughes comments out of this. Some great info here from him, also. It sounds strange, but I have always raced mono hull boats and only raced an outrigger hydro a couple of times. I have listened and learned from some of the best people in this sport to make the turn fins and other things that I offer. This thread ( and this web site ) is certainly a learning tool for me and many others who read here and can absorb all of the knowledge offered by experts such as Phil Thomas, Don Ferrette and Mike Hughes. Thanks guys!

Dick

 

[Glenn 787]

I received another fin (less bend, shorter and less blade area) from Dick on Saturday and ran it yesterday. It looked faster than last week. The tracking problem I had was almost eliminated, it still cornered well and no sign of lift. The only other change was a slight strut adjustment.

Thanks guys for sharing your knowledge on turn fins

Glenn

 

[Don Ferrette]

I received another fin (less bend, shorter and less blade area) from Dick on Saturday and ran it yesterday. It looked faster than last week. The tracking problem I had was almost eliminated, it still cornered well and no sign of lift. The only other change was a slight strut adjustment.

Thanks guys for sharing your knowledge on turn fins

Glenn

Ya gotta luv dem happy endings!

 

[Ron]

Glen 787,I can make you a turn fin for your Scale boat. All of the turn fins I make are made from 2024-T3 bare aluminum. The turn fins I make for Scale, Sport Gas and Sport 40 are made from .090 thick material. Sport 20 fins are made using .060 thick material. They are bent in a form with an Arbor Press so that I can duplicate the bend in each fin. Email me at "[email protected]" if you would like more information.

Thanks,

Dick

Dick,

I need a turn fin for my rigger. I've sent an email.

Please let me know if you do not receive it.

Thanks,

Ron.

 

[tnrcboatracer]

Ron, see this thread, Dick may not be making turn fins for a while. Maybe he or someone else has a fin you can use. Best to post in the for sale forum for what you are looking for.