Hydro Turn Fin Discussion

[BakedMopar]

First off I know there is alot of different shapes and sizes but is there a general rule with different styles of hulls. Hull in question is a 31" shovel nose. I see most run these types of hulls with a more straight style fin instead of a swooped style one. Is there a reason for this?

I know flex is not good but too thick will cause drag. Around what thickness and type of metal do you use ( I have 1/16"3070 and 1/8" 6061)?

What is your opinion on straight, hooks or bends?


I have read a lot from here and different forums but still would like a little more info.

Mahalo

[Fluid]

Plenty of folks run hooked fins on round nosed hydros. The fin design depends on the hull itself. Some hulls stay flatter in turns due to width or sponson shape, these can do well with non-hooked fins. Hulls which lift in the turns need something to keep them down. For example, my DarkHorse shovel like a hooked fin, but my Insane FE-30 turns great with a straight, angled fin.

A thin fin is good if there is minimal flexing. I prefer 1/16" aluminum, but not K&S metal, it is too soft. I have used tempered aluminum and even steel for fins with great success. But the mount needs to be substantial - nothing less than 1/8" aluminum angle stock.



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[BakedMopar]

Thanks Jay. I bought some commercial grade 1/16" but the only had it in 3070 and it ain't. That strong. Do you think the 1/8" will be too thick? I was thinking. Of going that route and just thin it out by putting a longer leading edge on it. I guess I'll just play around with different bends and hooks. Is there any starting point for lenght?

[Fluid]

Length depends on the water you run on and how flat the boat corners. The fin has to be long enough so that it does not unhook in a rough turn with the boat bouncing. It if unhooks you'll either slide out real wide, or trip and flip over.

With a good wedge shape the 1/8" fin will not be too bad in drag. For my money I'd rather have a boat that corners reliably than gain one mph on the straights. A floppy fin makes boat setup trying to say the least.


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[785boats]

I've read on the full size hydro forums where they measured a side loading of 4G in the turns on those fins. An unlimited hydro at 6,500lbs X 4 = A lot.
So I reckon that there is a substantial load on the turn fin in a model.
Anyone had a G meter in a scale Hydro?
I have bent 1/16" turn fins too easily in both hydros & monos, so I make mine out of 1/8" hard drawn stock. Don't know the grade I'm sorry. I don't know about the extra drag issue either, but they work fine & don't bend.
Most of the guys at our club run the hooked fin on the Shovels,
Here's a pic of the one I made for the 'Green Goblin' I finished last week. Maiden run last weekend was pretty good straight off the workbench.
Cheers.
Paul.

[properchopper]

George, the fin on the boat I made out of plain K&B aluminum. If you want a great fin to experiment with, Jan at Kintec has a straight .090 7075 aluminum fin sharpened and ready to go. It's harder than Chinese arithematic. Check out his site.

[BakedMopar]

Thanks guys. I already have a bunch of stock so I'll make a few different ones and test them out. I will be using the 1/8" 6061. I have some 7075 but that does not like to be bent.

Feel free to keep this going.

[BakedMopar]

Well I finished one fin today and will try it tomorrow. Really don't know if it will work but well see. Should be a learning experience! I have more time than money.

[Fluid]

That fin looks fine, but realize that the angle of the bend relative to the bottom of the hull can have a large effect on the boat's performance. I had one hydro which would not stay down on the water in the straights with a hooked fin. I tried every different strut setting I could but to no avail. Finally I loosened the turn fin and tinted it back a few degrees and voila - the boat ran awesome. Just a few degrees can make a big difference on some hulls. You will want to make your fin adjustable, use a single pivot bolt to tune it.



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[Jeff Wohlt]

A bad bent angle is worse than a straight fin. It can become a hydrofoil.

Why not start straight and then see where you are....you can then angle the fin if you have adjustable mounts. Some taper is good and sharp on the outside only.

Just watch how she lifts in the corners and adjust more angle in to it if needed.

[sailr]

I'm going to be following this thread closely as I embark on a 1/10th scale hydro project. Turn fins confuse the hell outta me! ;-)

[BakedMopar]

The fin that was on there had almost a 90 degree bend. It held nicely in the corners but on the straights in chop she would get flighty. It could be that it was too short so this one is 30% longer and slightly different shape. I do have another one that is the exact shape and size with no bends also to try today. The fin has around 15 degrees of adjustability also.

[Gary]

I just swapped out the fin on my PT Supersport and it did not like it at all. I went with shortend steel straight blade on a slight angle and the boat would not stay in the water on the straights and wanted to blow over. Ovcourse i figure it was not true and straight edged it many times to no avail. Put my Grim Fin back on and its fine. The Grim has a lot of flex so i will try another.

[teach]

I'm going to be following this thread closely as I embark on a 1/10th scale hydro project. Turn fins confuse the hell outta me! ;-)

A NAMBA type race 1/10th scale? If so there isn't alot you can do with it.

[jlinde1]

I'm a first-time poster from Marblehead, MA and am looking forward to learning more about the results Mahalo gets. I own a 1/10 scale, carbon fibre hydro - the Miss Hollywood Homes - built by the Campbell brothers in Washington state and run in the e-rcu series by Craig Mullen for the 2006-2008 seasons. Per the series rules, the boat originally had a 2” by 1” skid fin. Unfortunately, that fin departed the boat when I was running it for the first time on a local pond; it was clearly very functional - the boat flipped over immediately after the fin broke off! Since I had no plans to race the boat, I simply epoxied over the hole left in the sponson and have been making wide turns ever since. Now that I'm more comfortable with the boat, and getting tired of cornering at tugboat speeds, I'd like to replace the fin. I could go with the spec 2x1 fin, but since the boat is basically retired from racing, there's no reason not to experiment ...