Question about rudder placement, Sport-40

FloridaScaleBoater said:

Good morning guys,
Since the strut placement rule change for Sport-40/Q-sport hydro.
When mounting the strut on the transom vice under the hull, where are you placing the leading edge of the rudder in relation to the prop?
Those that are running transom mounted struts, are you using the extended struts or not?

Thanks all

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Samuel Hagan JR said:

View attachment 275796

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GRAHAME HAINES said:

I have always used the Les Ruggles principle of a rudder pivot angle of 17 to 18 degrees on all my hydros ever since I read his book on setting up scale unlimited hydros way back in 1982. He must have known his stuff because if I get in that range my boats turn with out effort and seem to go faster thru the truns than on the straight away. That may help with refining exactly where you can fit it John

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GRAHAME HAINES said:

I have always used the Les Ruggles principle of a rudder pivot angle of 17 to 18 degrees on all my hydros ever since I read his book on setting up scale unlimited hydros way back in 1982. He must have known his stuff because if I get in that range my boats turn with out effort and seem to go faster thru the truns than on the straight away. That may help with refining exactly where you can fit it John

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GRAHAME HAINES said:

Brandon/John. I have copied the section out of Les's book for you.

Bear in mind this was written way back when radio gear was not as good as it is now a days as our gear has a lot more grunt than back then but that pivot angle is still important to consider.

He talks about the rudder on the center line behind the prop as that is what all the old shovels had back then.

“The rudder is located on the transom and the skid fin behind the right sponson. The convenience that each boat does not have is the right amount of pivot between the rudder and turn fin.

It takes from 17 to 18 degrees of pivot for peak performance and long rudder servo life. Boats with too little pivot rely on more degrees of rotation buy the rudder in order to turn well. This constantly strains radio gear and shortens its life considerably. More pivot and less rudder rotation lets the hull do half the work and allows the radio gear to perform the way it was designed to do.

For example, Start with your rudder on the center line of your transom and turn fin in your desired place figure your degrees like this. First measure or calculate the distance from the skid fin to the center of the hull and write that figure down. Then measure from the rudder shaft to where the leading edge of the fin projects across to the center line of the hull.

Now divide the large measurement into the small one. What you get is the trig tangent for degrees. What you want is .305 to .325. those figures will give you the pivot you need. “

I still have my old log tables book I used at High school some 50 years ago and the tangent tables gets a fair bit of use setting sponson angles and rudder pivot.

For me then if I am over 18 degrees I move the rudder to the right till I get in the ball park and of course if I am under 17 degrees I move the rudder to the left. Mostly on the modern boats it always ends up on the right. I have even moved my turn fin back wards or forwards sometimes to help get that magic number.

Hope this helps

G

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Green Meany said:

hey grahame , I always remember reading yours and tony r s tech articles on hydros and set up etc with great interest , i havent been boating for about 15 yr and i turned to a hamilton race a couple of mths back and boy have things changed
terry wilson

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