Optimum shape/cross section for turn fins

[Mini Max]

I have seen a number of turn fins that are simply flat plates with a beveled leading edge. Would not a wedge be better?

[Team B&H]

Test. test, test some more

[Mini Max]

Ok, testing, thats a Maxum. A famous boat Italian boat designer I heard used to say, "Do exactly as I tell you, if it dosen't work do the oposite". I have a bunch of Carbon prepreg I need cook off. I made a plate version for Dudley Malone and he liked it quite alot. I was just thinking that I always made rudders for my inboard boats as a wedge.

[pirata]

The fin that came with my first boat was beveled on the outside edge. Front, bottom and rear but the inside edge was flat. My first year of racing I did a lot of testing, prop, engine angle, skid fin, etc... On a typical weekend I would burn 5 gallons of gas racing and 10 gallons testing. I tried 10 different fins I made in high school, shop class. I came to the belief that beveled inside and outside leading edge worked best. I also found a variety of bottom angles worked better than others. Varying depths worked for different couses. A course like Lawrence Lake 1 2/3 mile laps it worked best with the fin really high as the corners were long curves. Shorter courses with tight turns I liked a deeper fin and a longer length as well. By the end of that season I had 2 fins I liked best out of the original 10. I agree on the testing what works best for you and your setup.

[Mini Max]

If you still have the test boat, send me a drawing as to planform and attachment and I will make a wedge one to test in exchange for the results. I have a substantial amount of Carbon prepreg I am looking to convert to a product.

Jim Gardiner
Compmillennia, LLC.
Washington, NC 27889
www.compmillennia.com
(252) 628-8065 office
(252) 402-8810 cell
(866) 728-9633 fax
otseg@aol.com

[pirata]

Shoot. It's been 22 years since I graduated from high school. I have not raced since 1993 and all my stuff was sold sometime in the 90s. I remember a few shapes in my head but dimensions are definately lost.

[pirata]

One thing I forgot to mention about size and shape is I used my current turn fin as a reference in the ones I tried out. I made them varying sizes longer and/or taller and varying sizes smaller than the original fin. I tried crescent shaped, dagger shaped and straight shapes. I would also put multiple holes in each fin making it possible to adjust the height and distance behind the sponson for better or worse results. I will ask my father if he has any or our notes on testing we saved from back in the day but I am going to venture that he got rid of it with the rest of the stuff.

[heumanntouch7]

so, you are planning on making carbon fiber turn fins? that would be an awesome osy 400 fin. I would love to know when you have a product available.

[DiGia54D]

I ran a Carbon Fiber turn fin on my B&H CMH in 98. Never had a problem with it.

[GuyWithTheCoolBoat]

im not sure about turn friends but i have a family friend thats well known in the fine wood powerboat section of the market. they make their own rudders and they do a small taper towards a bigger trailing edge (point front blunt square back). i asked him one day... "wouldnt that be slower"... nope... apparently it reduces cavitation which is a major speed drag. dont know if that would apply here as their rudders are directly behind their props... but figured id chip in. hope its of use.

[Mini Max]

Making a thin wedge would be a pain in metal. In the big boats I have had a hundred of them cast in Stainless Steel or Bronze. I have made plate rudders and NACA sections too. The sailboats we always use a NACA section, even though some of them hit 40 kts believe it or not. I expect the wedges efficiency must kick in above that speed. I could do the wedge in carbon without too much difficulty.

If I can steal a moment I will price out some carbon plate in 1/8 3/16 and 1/4inch and see if there is a demand for stock where racers could cut out their own.

I have a 30' sheet of epoxy glass/carbon/glass laminate in plate form that is .227 inch thick which was left over from making the top skin for a tilt rotor landing deck to take 15,000 pound impact @ 4 G's. It would make a pretty good turn fin I would think. That black slab is 100% carbon fiber. No matter what the color, It's going to itch when you grind it.

[Team B&H]

Here's a few that we have tested- some all carbon, some carbon with a fiberglass core. Cored fins have unbalance carbon layup with more carbon plies on inside surface. We've been running composite fins for years with no problems save for one delamination (after 5 years of use) where the inside carbon delaminated from the the fiberglass which we think was due to the binder on the glass being intended for polyester resin and not epoxy. A switch to different glass cured that.

A tip from Bob Trolian: When working with fiberglass or CF dust, wipe yourself off with an old pair of pantyhose. New works OK too. The nylon fibers will pull the glass/cf fibers out of your skin and prevent most of the itching.

[Mini Max]

Very interesting collection of fins.

As prevention for itching we rub corn starch all over our bodies. Just like for Baby bottoms and around your neck and arms. I like the Lavender scent. Talc is not bad too.

We keep 30 gallon tubs of various fillers in stock. I showed a new hire how to apply the talc before grinding. The end of the next day he was on fire because he had used handfulls of milled glass fiber in error and had rubbed it all over his body and down his butt crack, just like baby powder. You only make that mistake once.

[pirata]

As prevention for itching we rub corn starch all over our bodies. Just like for Baby bottoms and around your neck and arms. I like the Lavender scent. Talc is not bad too.

Itching from what?

[Mini Max]

Itching from the dust generated from cutting and sanding Glass or carbon "fiber" composite laminate. It irritates the skin of most people. You have to be carefull of "green" epoxy laminate too because the dust can sensitize you to the epoxy.

I had a guy that took his lunchtime nap on the cutting table using a roll of chopped strand mat as a pillow. Conversely I had a designer that would get in the way some times and I would grind some fiberglass and he would be gone.