Making new style rudder for old style boat

Thread starter #1
Hello fellow Sunfishers,

As the title of the post says, I am making a new style rudder for my Sunrish which has the old style rudder hardware. Using the class rule book and drawing it all out, when I measure the angle between the leading edge of the rudder and the perpendicular line of the transom the angle appears to be 30 degrees. Does anyone happen to have that measurement handy. I suppose it really doesn't make much of a difference as none of it will be class legal, but I was curious.

Interestingly, my old rudder seems to be swept back much more. At first I thought the rudder hardware might be the difference, but the swing down plate seems to be parallel to the transom.

Thanks in advance for the help.
 

Webfoot1

Active Member
#2
It's 120 degrees between keel and leading edge of the rudder. If the rudder was vertical it would be 90 degrees so sweeping back
the rudder would add another 30 degrees for a total of 120 degrees. I think you have the correct angle already using your method.
The old rudder did have a bit more sweep. If you get a chance, switch to the new style rudder mount, it worth the effort in every
way.
 
Thread starter #4
I have seen the 120 degree angle both here in the forum and in the rules directly. The thing is that the bottom of the boat from which they make that measurement isn't 90 degrees to the transom nor is it straight. As we all know the bottom of the sunfish is curved making the measurement more difficult than say a Laser whose bottom is flat. Since the bottom curves downward from the transom, it would seem the angle of the rudder should be greater than 30 degrees.

Any thoughts?
 

Webfoot1

Active Member
#5
I've built two rudders using the above mentioned plans and a protractor and
they came out just fine. Other methods would be to use a transparency projector
to scale up the plans, draw them in a CAD program or find a existing rudder to
trace over. The rudder could be anywhere between 90 degrees and 120 degrees
and you would not loose any effectiveness. You have a lot (30 degrees) of leeway
to play with. I did lay a old rudder that someone made over what I drew up on
my wood blank and they matched exactly. I assume the old rudder was copied
from a factory original.
 

signal charlie

Well-Known Member
Staff member
#6
Did you look at the specification diagram? Sunfish Specifications | SailingForums.com

It says 120 degrees minimum, that is a class rule. The angle off a plumb transom will in fact be more than 30 degrees. Since you aren't worried about class legal you can make it vertical if you want, which is still debated as being more efficient. Or measure the angle between the transom and keel, let's say it is 15 degrees, and add 30 to that to come up with a 45ish degree angle. Or take the angle off of the diagram with a protractor. Or TLAR it (That Looks About Right). Take it off the old rudder if it was OEM. Or WAG it. Or SWAG it.

Have fun! Pics or it didn't happen!

Cheers
Kent
 

Webfoot1

Active Member
#7
Wooden rudder is useless for racing using the factory cross-section shown on the plans.
Guaranteed to go Braaaattttttt. . . every time. Giving it a true airfoil shape would help
more than the rudder angle.
 
Thread starter #8
Wooden rudder is useless for racing using the factory cross-section shown on the plans.
Guaranteed to go Braaaattttttt. . . every time. Giving it a true airfoil shape would help
more than the rudder angle.
Yes, that's the plan. Of course that complicates things a bit as the rudder isn't the same width from top to bottom.
 
Thread starter #9
I have been out of the country for two weeks, so rudder progress had been slow. I got going again today, and I thought I would share my progress.

I drew up the new rudder to scale on a piece of newsprint in pencil before I left, but I did not post, as the pencil lines did not show. I went over the plan today in ink so that everyone could see. Here it is:
 

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Thread starter #10
The next thing to do was to put an edge on a rough sawn mahogany board with the jointer, but first checking to see if the fence was square to the table. It was
 

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Thread starter #11
I want to make sure the rudder doesn't cup or warp, so rather than cut the shape from one piece, I am cutting the board into 2"+ strips on the table saw. Then I will glue the strips together to make a stronger more stable rudder.
 

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Thread starter #12
I then ran the strips through the thickness planer. I took off only a very small fraction on each pass, as I want to be sure when I am done I am at 3/4" thickness.
 

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Thread starter #13
Once the strips were cut, I made marks on the boards. The purpose of that was so that I could flip every other board over and have these boards also run lengthwise the other way. The idea is to make the board more stable.
 

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Thread starter #14
The last thing I did today was to run the strips on the jointer to get the cleanest edge possible, then I laid the rudder plan on top.
 

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Thread starter #15
I then ran the strips through the thickness planer. I took off only a very small fraction on each pass, as I want to be sure when I am done I am at 3/4" thickness.
The boards are now 13/16". I will lose that 1/16 overage later on.
 
Thread starter #17
H i everyone,

I thought you would be interested to see how the rudder I am building compares to the rudder I am replacing. The old rudder, circa 1971, was in tough shape. Where it was cracked I cut a kerf with the radial saw and then epoxied in shims. The outside edges were terribly splintered and to fix that I eopxied them together, best I could, and then used a hand plane and rasp to but to get back to solid wood so that I could varnish. How much of the rudder had been abraded away before the I was given the boat.

It was interesting to lay the old rudder over the drawing I made for the new rudder. The new rudder is much bigger as you can see. I am curious to see if I notice any difference when sailing. I also will be fairing the blade into a proper foil shape so that will likely have an effect as well.
 

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Webfoot1

Active Member
#18
The rudder will work better but the old style bracket may not. You may
find it "pops out/up" more often when under sail. The original bracket has problems with
the faster speed of racing sail/dagger-board/rudder.
 
Thread starter #19
The rudder will work better but the old style bracket may not. You may find it "pops out/up" more often when under sail. The original bracket has problems with
the faster speed of racing sail/dagger-board/rudder.
Hello. That's interesting. I have never had a problem with the rudder popping up, but I have read here that others have. I guess I will find out when this project is done.

I have personally never seen anyone use the new style rudder with the old style bracket, but I am sure it has been done. Have you ever used or seen anyone else do this? I don't know much about much, but I have never have heard that the manufacturer ever produced the new rudder/old bracket combination. Am I mistaken?
 
#20
I don't know much about much, but I have never have heard that the manufacturer ever produced the new rudder/old bracket combination. Am I mistaken?
Well, at my age I don't know about much anymore either, but your comment caused what gray matter I have left to sputter to life. Back in 1972 or so, Alcort, who made the boats back then, started selling replacement blades for the old style rudder that had the new shape. A number of them have been sold on the board - here is an example Old Style Sunfish Rudder Assembly A | SailingForums.com

You will notice they also offered a reinforced rudder head - both were improvements but nothing near as good as the new style rudder fittings.

Why did you make a bigger rudder blade? More blade = more drag. You want the rudder as small as possible while still being effective. That is one thing I still remember at my age.

It will be interesting to see if you notice a difference with a hydrofoil shaped blade. That is one thing I have never heard of anyone trying.

Gotta go. Time for my evening spinach, cod liver oil and Geritol! TUM
 
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