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Old 06-30-2019, 10:58 AM   #1
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What is this thingy on my rudder?

The trapezoid shape is the question. It appears to be welded/attached to the core rudder which is basically undisturbed. I'm 99% sure I can carefully take it off with no consequences to the rudder itself. I assume from an engineering standpoint it's a way to kick more water out during steering, therefore is either an add-on rudder attachment to make the rudder more responsive, or...

So I guess better stated:

0. Is my estimation as to it's function correct?
1. Is it factory?
2. Is it necessary?
3. Can I take it off?
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Old 06-30-2019, 11:29 AM   #2
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Google Fishtail or Thistle rudder. We have enough pilots and boat design guys here that can give you more info...but its a way to create more turning force with the rudder, I would assume that it has some sort of drag penalty though.
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Old 06-30-2019, 11:33 AM   #3
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The prop wash on the protrusions tend to keep the rudder straight and easier to run a straight course.
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Old 06-30-2019, 11:54 AM   #4
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Quote:
Originally Posted by bridaus View Post
The trapezoid shape is the question. It appears to be welded/attached to the core rudder which is basically undisturbed. I'm 99% sure I can carefully take it off with no consequences to the rudder itself. I assume from an engineering standpoint it's a way to kick more water out during steering, therefore is either an add-on rudder attachment to make the rudder more responsive, or...

So I guess better stated:

0. Is my estimation as to it's function correct?
1. Is it factory?
2. Is it necessary?
3. Can I take it off?
++++++ I do not see it in the photo.
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Old 06-30-2019, 12:09 PM   #5
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I’ve seen the wedge shape on one side of the rudder to help maintain a straight travel line to counter the effects of torque in a single engine boat.
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Old 06-30-2019, 12:29 PM   #6
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Dave Gerr claimed the thistle rudder offered better low speed maneuverability. It is an add on and can be ground off.
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Old 06-30-2019, 12:30 PM   #7
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It will help during slow speed handling and give more turning.

Sowhat beat me to it...
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Old 06-30-2019, 12:58 PM   #8
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Recent Thistle Rudder Thread

Great Harbour / Lou Codega Discussion
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Old 06-30-2019, 04:20 PM   #9
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Quote:
Originally Posted by OldDan1943 View Post
++++++ I do not see it in the photo.
Left half of it is broke/rusted off already. Half the right side is off too, and half the back part. In many ways it's already off, I just need to take the last bit off, I just didn't want to lose the intent of whoever added it on...

So it seems (and thanks for those who responded):

1. It's an add on.
2. It does what I thought generally (more rudder authority).

So my conclusion: I will take what's left of it off, see if I feel I lose anything and go from there. Since most of it is off already, I don't know what I don't have, therefore I don't think I'll miss anything.

If anything, I've learned what a thistle rudder is if I ever want to go there. Sometimes it's about knowing the words... "olive" hinge, "thistle" rudder, etc.

thanks!

(Oh, and I'd prefer to have the extra speed, even a tiny bit over a long journey can be meaningful.).
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Old 06-30-2019, 04:47 PM   #10
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I find the articulated rudder more interesting.
Of course, I will never get involved with one.
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Old 07-01-2019, 09:55 PM   #11
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For what it’s worth, we have a Manatee here locally that demonstrates the effectiveness of the rudder accessory in question. “Mango Mama” is likely one of the best handling examples out there, and he had his rudder done this way. He noted that his low speed turns were markedly improved. Later, after time-testing a new set of pneumatic stabilizers, he also had the tips of the stabilizer fins done the same way. Again, he noted a substantial increase in performance.

If there were consequences, it may be in the additional drag produced by the alterations. We both have Manatees with 140 HP Yanmar refits, and he may have lost about a half knot at the same RPM. Recently, he installed a steeper 22 x 17 prop recommended for the HP increase, and he reports the half-knot has returned.
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Old 07-01-2019, 10:24 PM   #12
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A three-degree rudder counteracts forward prop-walk for me. No need/desire for a wedge.
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Old 07-28-2019, 09:15 AM   #13
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if your thinking about a wedge on the rudder which helps backing and turning with a single engine boat, a Miami River shrimp boat Captain told me they had them on their boats years ago. He gave me a diagram and told me to make it out of starboard and bolt to rudder.
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