Sailboat rudder pulling to port

[dlochner]

After filling the rudder and replacing the skin, did you check the shape with the templates you made? Small deviations won't make a big difference unless you're racing.

How do you account for the difference between motoring and sailing?

Why was it necessary to rebuild the rudder? It looks like there is some damage to the lower forward end of the rudder? Was this a grounding? If there was a grounding, how hard was it? A hard grounding could cause the rudder post or rudder tube to be out of alignment.

 

[jviss]

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.

Thanks that doesn't look particularly precise.

 

[secondwind410]

After filling the rudder and replacing the skin, did you check the shape with the templates you made? Small deviations won't make a big difference unless you're racing.

How do you account for the difference between motoring and sailing?

Why was it necessary to rebuild the rudder? It looks like there is some damage to the lower forward end of the rudder? Was this a grounding? If there was a grounding, how hard was it? A hard grounding could cause the rudder post or rudder tube to be out of alignment.

The rudder worked fine for the last twelve years. The bearings started to have some play in them. The rudder always had water in it. ( since I owned it). I had put a drain plug in for winter storage. The bolts holding the quadrant on have always been seized. I know the foam inside it was not heavy enough. Time to do an overhaul. So the only thing that changed since last season and all was well then was a rebuild of the rudder and new bearings. The shape was checked frequently but it was always on its side. I didn’t have a vertical orientation. I beefed up the rudder trying to do it on the inside for the most part but put two layers of 1708 around the whole rudder and faired a bit of the “untouched side “ I thought it was close to perfect but I guess not. As you can see in the pic I still had part of the old fibreglass shape to work with. The rudder post stayed adhered to original glass on both sides.

After filling the rudder and replacing the skin, did you check the shape with the templates you made? Small deviations won't make a big difference unless you're racing.

How do you account for the difference between motoring and sailing?

Why was it necessary to rebuild the rudder? It looks like there is some damage to the lower forward end of the rudder? Was this a grounding? If there was a grounding, how hard was it? A hard grounding could cause the rudder post or rudder tube to be out of alignment.

The templates were checked frequently. Although they guided me they had a bit of flex. The rudder was fine last year. Reason for rebuild was water in rudder (12)years and now bearings had a bit of play. I believe the difference between sailing and motoring is propwash moving past the rudder at a much faster velocity. Probably equal to sailing at twice the speed. I kept the rudder post adhered to both sides, I kept the old glass on the nose, rudder post , trailing edge. These to I used as a guide. I didn’t have a vertical orientation of the rudder to check symmetry. It was always on its side

 

[dlochner]

So the only thing that changed since last season and all was well then was a rebuild of the rudder and new bearings.

I'm still leaning towards a poor alignment with the rudder shaft. I'm not familiar with how Hunter installed the bearings, but there might have been enough slop to have the bearings just slightly out of alignment. A couple of degrees over the course of 7 feet or so of rudder and post and the difference could be enough.

My theory on why you don't notice the turn when sailing, but do when motoring involves the amount of weather helm you have. For example if you typically sail with 5° of helm and the misalignment makes you sail with 8° of helm you may not notice the difference. If you trim the sails to reduce helm, you may be compensating with sail trim as well. However, when motoring in a straight line the helm is centered and when you try to steer the misalignment causes the boat to turn. Prop wash may accentuate the problem and a little uneven foil fairing might add some more, however, the prop wash is only about 20" in diameter with much more of the rudder untouched by the wash.

It might be possible to check the vertical alignment in the water, it will be a lot cheaper than a short haul. Use 2 plumb bobs, hang one from the very center of the transom so the weight hangs beneath the rudder. Hang another off the top aft corner of the rudder. The trailing edge of the rudder, and the 2 plumb bobs should all hang in the same plane. If the trailing edge of the rudder and the plumb bob on the rudder do not align, then the boat is listing or the rudder is not at a right angle to the hull. The leading edge of the rudder should probably be at a right angle to the centerline of the hull.

 

[sailme88]

The rudder is creating lift on the starboard side causing the bow to move left. This means that the speed of the water across the surface is faster on the fatter side so that it can catch up to the thinner side....

 

[secondwind410]

The rudder is creating lift on the starboard side causing the bow to move left. This means that the speed of the water across the surface is faster on the fatter side so that it can catch up to the thinner side....

So do you think the left or the right is fat, based on the boat turning to port ?

 

[secondwind410]

So this is my answer to check for symmetry.. a four foot long home made contour gauge.

 

[secondwind410]

So this is my answer to check for symmetry.. a four foot long home made contour gauge.

 

[dlochner]

So this is my answer to check for symmetry.. a four foot long home made contour gauge.

The dimension to look at is horizontal, not vertical for the foil symmetry. Four feet seems really large, is your rudder four feet wide? You'll also want to look at several stations, upper, middle, and lower.

 

[dlochner]

 

[JamesG161]

I will comment, but late to this discussion.

Symmetry is ideal but not a killer to balanced streamlines or the " air foil " effect.

To disrupt a streamline, as is done on air craft wings, automobile spoilers, and golf balls, you change the pressure difference on the surfaces, as the fluid flows past.

One possible idea is to build up the trailing edge of the rudder on the side of the "pulling".
Similar to the "Flaps" on a aircraft wing.

That small resin build up can be adjusted by sanding, if you have the inclination to do so.
Jim...

 

[secondwind410]

I will comment, but late to this discussion.

Symmetry is ideal but not a killer to balanced streamlines or the " air foil " effect.

To disrupt a streamline, as is done on air craft wings, automobile spoilers, and golf balls, you change the pressure difference on the surfaces, as the fluid flows past.

One possible idea is to build up the trailing edge of the rudder on the side of the "pulling".
Similar to the "Flaps" on a aircraft wing.

That small resin build up can be adjusted by sanding, if you have the inclination to do so.
Jim...

Any idea what thickness we are talking about

 

[secondwind410]

The dimension to look at is horizontal, not vertical for the foil symmetry. Four feet seems really large, is your rudder four feet wide? You'll also want to look at several stations, upper, middle, and lower.

Yes I will check it horizontally every 2-3 “

 

[JamesG161]

Any idea what thickness we are talking about

I would guess only 1/4" to over kill.

The prop wash only disturbs the streamlines on a small part of the rudder directly behind the prop.
By accident, I had the bottom painted incorrectly RED, then they had to overpaint with Navy Blue. Recently my diver could then see the missing Blue and the Red showing through on my H430. Perhaps about 10" was the RED revealed.

Remember a disturbed streamline has little effect on a hard over rudder position. Only perhaps < 8° would it matter.
Jim...

PS: The more the rudder angle the less foil effect.

 

[secondwind410]

I would guess only 1/4" to over kill.

The prop wash only disturbs the streamlines on a small part of the rudder directly behind the prop.
By accident, I had the bottom painted incorrectly RED, then they had to overpaint with Navy Blue. Recently my diver could then see the missing Blue and the Red showing through on my H430. Perhaps about 10" was the RED revealed.

Remember a disturbed streamline has little effect on a hard over rudder position. Only perhaps < 8° would it matter.
Jim...

PS: The more the rudder angle the less foil effect.

So if the boat wants to turn to port/ wheel counter clockwise would I thicken the port side trailing edge ?

 

[JamesG161]

You want to disrupt the side opposite the pull, therefore reducing the pressure on that side.
I would think Starboard side.
Jim...

 

[secondwind410]

You want to disrupt the side opposite the pull, therefore reducing the pressure on that side.
I would think Starboard side.
Jim...

Here is the rudder in the orientation it wants to go. What do you think. Port or starboard?

 

[jviss]

Symmetry is ideal but not a killer to balanced streamlines or the " air foil " effect.

But absolutely necessary for a boat rudder, and an airplane rudder, for that matter.

Similar to the "Flaps" on a aircraft wing.

No, not flaps, but trim tabs. Very different control surfaces.

 

[dlochner]

If the issue is the foil shape, then the side of the rudder that was not removed should be undisturbed. This is the side to template. Then move the template to the other side of the rudder at the same height. You will quickly know how out of shape the starboard side of the rudder might be.

We can speculate and theorize all day, however, until the boat is hauled and the rudder templated and the rudder post and rudder checked for alignment, all this is simply a mental exercise.

The cardboard templating tool the OP developed is a clever idea. I don't know if it will work, but it is clever.

Maybe we should start a GoFundMe page to help the OP raise the money to haul the boat.

 

[jviss]

Maybe we should start a GoFundMe page to help the OP raise the money to haul the boat buy the OP a new rudder!