Mac25 optimum rudder angle

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Kestle

Kestle

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Jun 12, 2011
702
MacGregor 25 San Pedro
Idiot me got caught with genoa only in a narrow channel and couldn't make it. I would have, if I was flying a 100 and not the 150. The air was light and after a few tries I began to wonder if part of my tracking issue related to my rudder position, which was straight down. It was not the time to experiment.

Anyone formally calculated optimum rudder angles for a beat in these swing keel boats?

Jeff
 
M

Mike B1026

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Jun 17, 2007
402
MacGregor Mac26S Victoria Tx
Have never heard of a reason to alter the rudder position. As long as it is straight down.
 
Kestle

Kestle

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Jun 12, 2011
702
MacGregor 25 San Pedro
Mike B1026 said:
Have never heard of a reason to alter the rudder position. As long as it is straight down.
Click to expand
I'm more used to newer race boats with bulb keels...the geometry on the are different that those or dingy sailors. The keel angle is quite a bit off vertical.

No, I never took fluid dynamics.

Jeff
 
timebandit

timebandit

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Jun 3, 2004
1,863
Macgregor 25 So. Cal.
Because you mention bulb keels I take a chance that you meant keel instead of rudder.

You mention a bulb keeled racing boat, I bet it was not moveable.

If you look at the line drawing on page five of this document
http://macgregor.sailboatowners.com/images/kb/pdf/647.pdf

You will notice that the keel in the locked down position has it bottom approx. parallel to the water line and the center of latteral ristance about 12 inches aft of the fwd edge of the rear window.

Having the keel hanging straight down the center of lateral ristance may move fwd to aprox. 12 inches fwd of the rear of the front window, also I wonder if the keel would swing back and forth in relation to the water line when going up and down a wave moving the center all the time.

Allowing the keel to rest on the lock bolt as many sailors do moves the center of lateral ristance even further back than locking it in place.

Where does the keel belong?

The manual sez to use the locking bolt in the hole to position it in the correct position.

You couldn't move you bulb keel, you cannot move a dagger board fwd or aft, and the little swing keel on an S model is usually run all the way down, so why move the keel on a 25.

There may be some speed running DDW by raising the keel fully but the boat will be very tender and if you broach you will be in deep dodo.

The only reason the keel moves is to get the boat on and off the trailer.

That's my story and I am sticking to it.
 
Kestle

Kestle

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Jun 12, 2011
702
MacGregor 25 San Pedro
timebandit said:
Because you mention bulb keels I take a chance that you meant keel instead of rudder.

You mention a bulb keeled racing boat, I bet it was not moveable.

If you look at the line drawing on page five of this document
http://macgregor.sailboatowners.com/images/kb/pdf/647.pdf

You will notice that the keel in the locked down position has it bottom approx. parallel to the water line and the center of latteral ristance about 12 inches aft of the fwd edge of the rear window.

Having the keel hanging straight down the center of lateral ristance may move fwd to aprox. 12 inches fwd of the rear of the front window, also I wonder if the keel would swing back and forth in relation to the water line when going up and down a wave moving the center all the time.

Allowing the keel to rest on the lock bolt as many sailors do moves the center of lateral ristance even further back than locking it in place.

Where does the keel belong?

The manual sez to use the locking bolt in the hole to position it in the correct position.

You couldn't move you bulb keel, you cannot move a dagger board fwd or aft, and the little swing keel on an S model is usually run all the way down, so why move the keel on a 25.

There may be some speed running DDW by raising the keel fully but the boat will be very tender and if you broach you will be in deep dodo.

The only reason the keel moves is to get the boat on and off the trailer.

That's my story and I am sticking to it.
Click to expand
No, I was making a comment/asking a question on the difference in keel designs impacting leading/trailing edge angles on the rudder position for different points on the wind. The rudder is clearly designed to be used at different angles ( note it is not just a kick up rudder)

Forget the stuff on bulb keels.

Jeff
 
Jackdaw

Jackdaw

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Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Kestle said:
No, I was making a comment/asking a question on the difference in keel designs impacting leading/trailing edge angles on the rudder position for different points on the wind. The rudder is clearly designed to be used at different angles ( note it is not just a kick up rudder)

Forget the stuff on bulb keels.

Jeff
Click to expand
Are you talking rotational angles, or for/aft angles?

If you are talking rotational angles (how far the tiller is one way and the rudder the other), you should have it no more that approx 7 degrees off straight if you are trying to sail in a straight direction. If you go more than this, the rudder 'stalls' as a foil and does not generate any lift. As an aside, most broken rudder stories I hear are about people beating with their rudder pulled hard over, trying to correct some wicked weather helm. That will break any rudder.

If you are talking for/aft, sometimes you can adjust that to affect the balance of the rudder. A rudder is 'balanced' when a portion of the control surface is in from of the pivot point, and makes it easier to turn. That adjustment is set mostly on feel.

EDIT - but if i re-read your question, you boat probably had some huge lee helm with the 150 up. Its known to be under-ruddered anyway. Not sure anything you could do with your existing rudders to help that.
 
timebandit

timebandit

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Jun 3, 2004
1,863
Macgregor 25 So. Cal.
Here is a picture of my Ida rudder and as you can see it will run straight down the reverse shear of the transom.

This design with a nacca 12 airfoil is very powerfull and works well for me even though not any longer or wider that the one it replaced witch was hollow fiber glass.

The first time out I noticed little or no sound or bubbles left in the rudders wake.

I pin my rudder in the fully down location so that it can not move.
 
Kestle

Kestle

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Jun 12, 2011
702
MacGregor 25 San Pedro
Jackdaw said:
Are you talking rotational angles, or for/aft angles?

If you are talking rotational angles (how far the tiller is one way and the rudder the other), you should have it no more that approx 7 degrees off straight if you are trying to sail in a straight direction. If you go more than this, the rudder 'stalls' as a foil and does not generate any lift. As an aside, most broken rudder stories I hear are about people beating with their rudder pulled hard over, trying to correct some wicked weather helm. That will break any rudder.

If you are talking for/aft, sometimes you can adjust that to affect the balance of the rudder. A rudder is 'balanced' when a portion of the control surface is in from of the pivot point, and makes it easier to turn. That adjustment is set mostly on feel.

EDIT - but if i re-read your question, you boat probably had some huge lee helm with the 150 up. Its known to be under-ruddered anyway. Not sure anything you could do with your existing rudders to help that.
Click to expand
It is the fore/aft balance I was referring to. Mine is pinned down vertically.

Perhaps this is the real answer...that the boat is under-ruddered and I notice it more than others as I sail on multiple boats often. It wasn't a lee helm issue, I just couldn't track or point at all in that narrow space (i.e. I couldn't get sufficient speed up). Plus, the sail isn't barber hauled easily, even when partially furled.

The whole exercise was a bit silly btw. I was only going about 100 yards, and I had just had the motor winterized and didn't want to put it in unless I had to. Still, it was a learning experience.

I had an offer of a storm jib, one of those that fits over a furled sail. Anyone have experience with how they point in light air on these boats?

Jeff
 
M

Mike B1026

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Jun 17, 2007
402
MacGregor Mac26S Victoria Tx
Like I said before, never heard of "adjusting a rudder. By raising it up it will increase weather helm and put a lot of stress on tiller/rudder. Sounds like you weren't up to speed and had no steerage?
 
Kestle

Kestle

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Jun 12, 2011
702
MacGregor 25 San Pedro
timebandit said:
Where were you, coming from Queens Gate to Angels Gate behind the sea wall?
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No (highly embarrassed look) I was moving from a transient slip on D dock at HH to the lifts. The path is always straight upwind to the lifts, and you have about a 50 foot channel to tack in.

But you are close...

Lucky me...there was even an audience. At least going back to D dock I didn't screw up!

:) Jeff
 
Kestle

Kestle

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Jun 12, 2011
702
MacGregor 25 San Pedro
Mike B1026 said:
Like I said before, never heard of "adjusting a rudder. By raising it up it will increase weather helm and put a lot of stress on tiller/rudder. Sounds like you weren't up to speed and had no steerage?
Click to expand
That pretty much sums it up...

Jeff
 
timebandit

timebandit

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Jun 3, 2004
1,863
Macgregor 25 So. Cal.
:DI built a couple of paddles like this but I found out they worked better without the holes.:D

Isn't the aft dock line a little small?;)

 
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