Sailboat rudder pulling to port

Mar 5, 2009
57
Hunter 410 Penetang
Ok so I took my hunter 410 out for the first time since rebuilding my rudder. 4.7 knots under power and it starts to pull to port. Sailing at 5.4 and no pull, didn’t get her faster than that on that given day. Boat pulls and turns to port, wheel turns counter clockwise, rudder is oriented with the leading edge pointing starboard and trailing edge pointing to port. I believe it is out of symmetry. Any thoughts as to which side would need to be reduced? Port or Starboard ?Any ideas as to how to check symmetry? Any thoughts as to which is most important, trailing edge or leading edge and what tolerances we are talking about. I am a little confused on foil theory and what the pull to port would indicate with regards to the shape and which side to reduce ?
 
Jan 19, 2010
12,362
Hobie 16 & Rhodes 22 Skeeter Charleston
Do you have pics of the rebuild and installation?
 
Jan 11, 2014
11,322
Sabre 362 113 Fair Haven, NY
Is the rudder centered with respect to the wheel? there should be an equal number of turns to go from centered to port and center to starboard. When the wheel is centered, the rudder should be aligned with the centerline of the boat.

The cables on the steering quadrant need to be adjusted. Center the wheel. Loosen the adjusting bolts on the quadrant. Center the rudder. Tighten the adjusting bolts equally on both sides, a little at a time going back and forth until the steering cable is taut.
 
Jan 11, 2014
11,322
Sabre 362 113 Fair Haven, NY
I cut away one side leaving the edges and the post attached to the fibreglass. Replaced the foam, added fibreglass to the inside, filled with 15lbs foam and several layers of glass over both sides. Very happy with it until I felt the pull to port
Typically there are flanges welded to the rudder post extending into the rudder. Without the flanges, the rudder post could slip and no longer be oriented correctly. That could be part of the issue. Do you have photos of the post itself above the rudder?

Here's a video from Boatworks Today on rebuilding a foam cored rudder. It is the first of a series of videos on the rudder rebuild.

 
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Likes: jssailem
May 17, 2004
5,028
Beneteau Oceanis 37 Havre de Grace
If there’s no pull when sailing on either tack I wouldn’t assume it’s a rudder issue. Our boat pulls to starboard when motoring, and straightens our as soon as we stop the motor. I attribute it to prop wash and torque from that.
 
Jan 11, 2014
11,322
Sabre 362 113 Fair Haven, NY
If there’s no pull when sailing on either tack I wouldn’t assume it’s a rudder issue. Our boat pulls to starboard when motoring, and straightens our as soon as we stop the motor. I attribute it to prop wash and torque from that.
I guess the question to ask, did it have this problem before the rudder repair? If this is a new problem then the repair may be suspect, if it is just the recurrence of a previous problem, then it may well be just the prop wash.

It could also be a misalignment of the steering cables that accentuates the prop wash or the shaft could have shifted during the repair.

Another question, how is the steering quadrant attached to the rudder post? Does it have a through bolt?
 
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Likes: jssailem
Jan 19, 2010
12,362
Hobie 16 & Rhodes 22 Skeeter Charleston
foils produce lift and if the two sides of your rudder are not symmetric, they will produce different amounts of lift. Here is what I would do (I made a diagram)...

1592862461250.png


Lay your rudder (black and grey image) on a table (brown block in picture). Lay a level on the rudder post and shim until your rudder is laying level on the table. Find a piece of wood trim (thick red horizontal line) and suspend it level over the rudder. Take measurements to the surface of the rudder and write those down right on the surface of the rudder. Turn the rudder over and repeat. Next compare the two sets of numbers. You should be able to identify high spots and sand those down until the two surfaces are symmetric. This will be very tedious because your rudder has curves in more than one plane so you will have to move the rudder forward and back and repeat this process many times making many marks on the surface of the rudder. But when you are done marking the rudder, just put a sander on the big numbers and then remeasure to see if you got them all about the same.



Edit: I'd check what @Davidasailor26 suggested before doing all the work I just outline.:facepalm:
 
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Likes: LloydB
Mar 5, 2009
57
Hunter 410 Penetang
I guess the question to ask, did it have this problem before the rudder repair? If this is a new problem then the repair may be suspect, if it is just the recurrence of a previous problem, then it may well be just the prop wash.

It could also be a misalignment of the steering cables that accentuates the prop wash or the shaft could have shifted during the repair.

Another question, how is the steering quadrant attached to the rudder post? Does it have a through bolt?
This is a new problem after the rudder rebuild. It always tracked straight under power. I think the prop wash accentuates the symmetry problem. The quadrant can only go on one way with a big bolt. The rudder post was never taken out of the rudder. Very much the same as the Boatworks video.
 
Jan 11, 2014
11,322
Sabre 362 113 Fair Haven, NY
Is the bolt hole still aligned with the rudder? It needs to be perfectly aligned with the center of the rudder.

Prop wash will accentuate any alignment error. Under sail there is usually less pressure on the rudder, especially if the sail trim is good and balanced.

My best guess is the rudder post is not proper alignment in one or more dimensions. The bolt hole for the quadrant may be off a few degrees, the rudder post may be canted a few degrees fore or aft, or port to starboard.

Small deviations in the rudder foil shape probably won't have much noticeable effect, large deviations would and would be visible by eye.

How did the rudder post get pushed out of alignment. Fiberglass doesn't stick all that well to SS, while removing all the old foam the bond between the post and rudder was loosened. The expanding foam pushed the rudder post out of alignment. It wouldn't take much movement, a few millimeters at the base of the post will make a big difference at the top of the post a few feet away.

The alignment of the quadrant bolt hole can be checked with the boat in the water, center the rudder and look to see if the quadrant is aligned correctly. Don't rely on the wheel to center the rudder, have someone inspect the rudder under the water. Alternatively, center the quadrant and then inspect the rudder to see if it is aligned correctly. (The latter is probably easier.)

Checking the alignment of the rudder post in the rudder will probably require hauling the boat and dropping the rudder.
 
Mar 5, 2009
57
Hunter 410 Penetang
Is the bolt hole still aligned with the rudder? It needs to be perfectly aligned with the center of the rudder.

Prop wash will accentuate any alignment error. Under sail there is usually less pressure on the rudder, especially if the sail trim is good and balanced.

My best guess is the rudder post is not proper alignment in one or more dimensions. The bolt hole for the quadrant may be off a few degrees, the rudder post may be canted a few degrees fore or aft, or port to starboard.

Small deviations in the rudder foil shape probably won't have much noticeable effect, large deviations would and would be visible by eye.

How did the rudder post get pushed out of alignment. Fiberglass doesn't stick all that well to SS, while removing all the old foam the bond between the post and rudder was loosened. The expanding foam pushed the rudder post out of alignment. It wouldn't take much movement, a few millimeters at the base of the post will make a big difference at the top of the post a few feet away.

The alignment of the quadrant bolt hole can be checked with the boat in the water, center the rudder and look to see if the quadrant is aligned correctly. Don't rely on the wheel to center the rudder, have someone inspect the rudder under the water. Alternatively, center the quadrant and then inspect the rudder to see if it is aligned correctly. (The latter is probably easier.)

Checking the alignment of the rudder post in the rudder will probably require hauling the boat and dropping the rudder.
I know the post hasn’t moved. It is a composite post and was very well attached. I had one half of the post exposed to the trailing side so I glass five layers of 1708 down the side of the post and onto the inner body of the rudder. She isn’t moving. The rudder post had a hole right through it at the top. It has a large bolt going through it and the stainless band and the quadrant. It can only go in one way.
 
Jan 22, 2008
296
Islander Freeport, 41 Ketch Longmont, CO
SO this is here you probably need to learn a bit about foil theory and how they work. Your rudder should be balanced port/starboard regardless of prop wash, sail trim or any other factors. The foil should be the same on both sides as well as top to bottom. Take the boat out for a spin, run it up to hull speed, put the transmission in neutral and see how the boat tracks with no prop wash. Does it pull to either side? or does it track straight. If it pulls to either side then you do not have an even foil on the rudder. My guess is when you laid it flat you didn't get a perfect match on the both sides of the rudder.

I would suggest finding a way to check the foil on both sides to ensure they match. If they do not match then you get to decide to add more or less to fix the problem. Do a search on NACA foil theory or rudder foil theory and learn a bit about the requirements for a good rudder foil. If you have the technical know how to repair the rudder, then you can figure this out. It will be a fun project. Keep us posted on your progress.

Fair winds.
 
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Likes: jssailem
Mar 5, 2009
57
Hunter 410 Penetang
SO this is here you probably need to learn a bit about foil theory and how they work. Your rudder should be balanced port/starboard regardless of prop wash, sail trim or any other factors. The foil should be the same on both sides as well as top to bottom. Take the boat out for a spin, run it up to hull speed, put the transmission in neutral and see how the boat tracks with no prop wash. Does it pull to either side? or does it track straight. If it pulls to either side then you do not have an even foil on the rudder. My guess is when you laid it flat you didn't get a perfect match on the both sides of the rudder.

I would suggest finding a way to check the foil on both sides to ensure they match. If they do not match then you get to decide to add more or less to fix the problem. Do a search on NACA foil theory or rudder foil theory and learn a bit about the requirements for a good rudder foil. If you have the technical know how to repair the rudder, then you can figure this out. It will be a fun project. Keep us posted on your progress.

Fair winds.
Thanks
 

jviss

.
Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
When you rebuilt the rudder, how did you recreate the airfoil shape on the new side? If you didn't really pay attention to this aspect, then that is probably the root of the problem. Even a slightly different shape on a side can cause what you describe.

This isn't something you can "eyeball." You would need some kind of template or form to get the shape desired, and to make sure its symmetrical.

Water is quite dense, almost 800 times more dense than air; even very small differences in underwater foils will be noticed.

There are several common techniques for cutting the airfoil shape, from cutting the foam with a hot wire down to ribs built into the rudder; to routing the foam using an external template; to assembling pre-cut pieces into the overall form. But if you're not following an explicit airfoil shape and using a template, there's little hope of getting something symmetrical, let alone 'correct.'
 
Jan 19, 2010
12,362
Hobie 16 & Rhodes 22 Skeeter Charleston
What I described in post #9 above is not just a theory. I've done it. I had to rebuild a rudder from scratch for a Macgregor 22. It was a simple wooden rudder but I put a foil shape to it. To ensure the two sides were correct, I took a piece of old wood trim out of my shed and marked off distances to the surface of the wood on each side of the rudder, then knocked off the high points on the rudder surface with a plane.
Rudder_Repair5.jpg
 
Mar 5, 2009
57
Hunter 410 Penetang
When you rebuilt the rudder, how did you recreate the airfoil shape on the new side? If you didn't really pay attention to this aspect, then that is probably the root of the problem. Even a slightly different shape on a side can cause what you describe.

This isn't something you can "eyeball." You would need some kind of template or form to get the shape desired, and to make sure its symmetrical.

Water is quite dense, almost 800 times more dense than air; even very small differences in underwater foils will be noticed.

There are several common techniques for cutting the airfoil shape, from cutting the foam with a hot wire down to ribs built into the rudder; to routing the foam using an external template; to assembling pre-cut pieces into the overall form. But if you're not following an explicit airfoil shape and using a template, there's little hope of getting something symmetrical, let alone 'correct.'
Thanks for your reply. I used melted strips of plastic. I thought it worked ok but I guess not. Trying to think of the best and easiest method to check it now. Going to use a contour gauge for the front nose. Not sure about the sides.
 

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