? for Preston Hall

[Allen Waddle]

Preston,

In the outboard forum you stated the following:

"Turn fin principal..............well a feathered race-course-side edge makes a lower pressure to that side and therefore pulling the boat to the inside. True. But I took the stock SGX fin off, put on a feathered edge, increased left trim and went 2 mph faster with no other changes. So the drag of the blunt edged fin was more than that of the left trimmed rudder.

I would like to know more about this experiment. I know that left trim will tend to loosen the boat up. Does the boat seem looser to you?

I guess I am just trying to figure this comment out. Common sense tells me that the rudder trimmed to the left has to cause more drag than the mitered edge turn fin.

I sure hope that there is something you are overlooking as I have spent a great deal of time this winter trying to make a turn fin that will allow a couple of my boats to go straight without the left trim (I relize i may have to take shim out of here or thereor strut changes). I also understand that I am asking impossible questions such as did it loosen the boat up as there is no possible way to measure this.

There is also atleat one more possibility as to what you saw. With the left rudder the water to the engine was less which could net greater speeds.

I know that there is no one answere that will work in every case and the only way to figure out what will work for each person is to try it but I am trying to learn more from your experience so that i can get new ideas to try.

Thanks for your help in advance.

Sincerely,

Allen Waddle

 

[Preston_Hall]

1) The boat was not any more loose.

2) Common sense might make you think that the feathered edge is less drag as well. So in that thinking, the fin is more drag than the rudder? And I'll throw this at you. The boat was no faster without the fin. Same goes for the .12 I ran. The .12 was actually faster because I could carry more speed through the turn before lining up for the SAW.

3)I doubt I overlooked anything. The change took only a couple of minutes. Radar gun in hand. Don't know why you would change the strut. Mine are all straight. If you need the boat to track left then you make the left sponson tighter to the water.

4) Water was spewing as hard as ever. You know, John Finch taught me a while back that a quick way to set the rudder is to make the right rudder face parallel with the right side of the boat. This method puts you very close.

But you are correct, different things work for different people. I have had the privilage of personnaly knowing John Finch and Kentley Porter and have learned that your can take a lot of these concepts and throw them out the window. See what the boat does and make corrections from there. Short rudders stink and I have never gained any speed from them. A longer rudder actually seems to go faster through the turns due to more control and less required rudder throw. It also will allow you to ease left much easier.

Get a good engine, good boat, a great setup, the correct prop and you can race the best.

 

[Allen Waddle]

Thank you for the you input. While I have tried some of the things that you speak of, you have sparked atleat one more idea and provided away to test the efficency of turn fin sharpening that I have never thought of.

Sincerely,

Allen Waddle