Turn Fin Theory

[Toni Lightbourne]

Hello All. I've been wondering what's the different effects regarding turn fin placement. Some hulls I see turn fins all the way to the outboard of the hull and others I see stepped in about an inch inline with the chine of the hull. Also see guys running their fins straight up and down instead of perpendicular with the flat surface of the hull. What are the theories and characteristics of this process?

 

[Wasted wages]

I assume you are talking about mono's....

As the hull rolls in the turn, the angled fin will now be running down into the water providing more bite.... as the hull rolls out of the turn, the fin now lifts out of the water lessening the drag..

If the fin is mounted straight up and down, when the hull rolls into the turn, the fin can start acting like a lifting surface and upset the boat. plus it creates drag all the way around the course.

 

[john v]

if you get a chance pick up one of john finchs books on rc boat racing, he has a couple of pages dedicated to turn fins, great book!. my 3 books i have are one of a kind tho, they were autographed by the master himself!

 

[Toni Lightbourne]

Thanks very much guys. I will look for that publication.

 

[Daniel's Racing]

You usually get best effect my going out as far as you can and be 90° to the bottom.

The leading edge angle and setback are the huge tuning areas to test.

The straighter and/or closer to transom will make the boat much more responsive to rudder input. Not really what you want though. It is like driving with steering speed on full blast in some cases if too straight or close.

Spent many trips to the lake testing turn fin shapes and best angle for the leading edge while designing my titanium mono turn fins. They are amazing fins. Handling is awesome as is the cornering speeds on everything from stock monos to the Superboats.

Having good surface area from bracket to fin is very important. Fin gets kicked back during a race and your done. It has to stay where you set it.

Brackets down low and outboard as far as you can. The further out the better they work and the more they are lifted when boat is going straight so your not dragging fins in the straight aways.

 

[Toni Lightbourne]

Thanks Daniel. Just the info I was looking for. Check this sketch. I see some guys run their fins straight up and down as opposed to perpendicular to the bottom. Didn't seem to bother him at all. You're method is great thanks again.

 

[Mario Johnston]

I'll elaborate on your drawing just a bit more with how I run my SS mono fin:
The fin is perpendicular to the hulls right floor, length of the fin stops around the depth of my prop hub/stinger. In this way, the fin has minimal effect on the boat while on the straights, however with right rudder, the hull leans in and the fin drops into the water and begins to dig for the corner.

 

[Toni Lightbourne]

Wonderful. Thanks so much for that info as well. Much appreciated.

 

[Toni Lightbourne]

if you get a chance pick up one of john finchs books on rc boat racing, he has a couple of pages dedicated to turn fins, great book!. my 3 books i have are one of a kind tho, they were autographed by the master himself!

Where can I find a copy of this book?

 

[john v]

Where can I find a copy of this book?

i got my books at a lhs maybe 20 years ago, not sure maybe ebay?. but well worth the search

 

[Marty Davis]

You can also find many technical papers at: Tune & Modify RC Nitro Engines | RC Nitro Engine Analysis Software including turn fin theory.

 

[LohringMiller]

Those were great articles and inspired much of our work on dyno testing and data acquisition that we used in the early 2000s. They are as valuable today as they were then. Thanks for posting them.

Lohring Miller