Rudder question

[saburke17]

How much can rudder alignment affect performance? When the yard pulled my rudders to repack them, i noticed that they are now 5 degrees off so i have keep the wheel 5 degrees to port to go straight. i also noticed the are not parallel to each other one is say 2 or so degrees out of whack. adjusting them back to 0 degrees will be fairly simple albeit a pain in the A$$ but should both rudders be set a 0 degree's?

[Tommy]

Here you go, Saburke, from Power & Motoryacht Magazine:

Rudder Mysteries

If you don’t want your boat to take you somewhere you don’t want to go, you should know a thing or two about rudders.
Rule of thumb: incorporate a little bit of toe-in on the rudders based on outboard-turning props.

A while back, Capt. Bill Pike and I were discussing our nautical misadventures, trying to one-up each other with unusual, often unexplainable, occurrences we’d managed to survive: Racing sloops on the rocks, dockings so disastrous they were covered by The New York Times, rescues by the U.S. Navy shore patrol—the usual stuff. Then Bill recalled testing a new boat a couple of years ago, when the boat tried to make its escape. Seems that when Bill cranked on the throttles, as he is wont to do, the boat decided to stop answering the rudders and took off port and starboard, willy-nilly, heedless of the wheel. Throttled back, she regained her composure. What the heck?

Back at the dock, with the boat in the slings, the culprit was quickly identified: the rudders were toed-out about half an inch; the designer had spec’d that they be toed-in by the same amount. A quick adjustment of the tie bar put things right, and the boat subsequently behaved just as you’d expect at all speeds.

What’s toe-in and toe-out? Rather than the rudders running straight fore and aft, parallel to the boat’s centerline and to each other, they are angled in or sometimes out just a bit. Most designers consider toe-in to be when the leading edges of the rudders are closer together than the trailing edges. But sometimes there’s a problem of definition: One man’s toe-in is another’s toe-out.

Why Aren’t Rudders Straight?

You’d think if you wanted a boat to go straight, the rudders ought to be straight, too. Not so, said Chris Critchett, a naval architect with Michael Peters Yacht Design: The rule of thumb is to incorporate a little bit of toe-in on the rudders, based on outboard-turning propellers on a V hull. It’s a result of how the water flow coming off the propeller hits the rudder: It makes most rudders want to aim inboard a little bit. But today many propellers are in tunnels, and that can change the rules.

Adjusting rudders often means following a sea trial with mathematics

Powerboat rudders on planing boats are relatively short, explained naval architect Dave Gerr, and operate in the top half or two-thirds of the slipstream from the propeller. The rudder’s natural tendency is to follow the water flow; with outboard-turning props, the pressure tends to rotate the rudders outboard, i.e., toe them in. “Mike Peters is one of the few guys who specify rudder toe,” said Gerr. “That’s one reason his boats are so good.” According to Gerr, 90 percent of conventional powerboats have rudders aligned with each other and with the centerline. “It’s cheaper, quicker and easier, and works for most people,” he said. But properly toed-in rudders reduce drag, give crisper steering and more speed. Only thing is, he added, “there’s lots of stuff going on under the boat, and nobody totally understands it.”

How much toe is enough? Both Critchett and Gerr agree that the best way to set the rudders is to run the boat in a straight line, at moderate speed, and disconnect one rudder. Let it free-trail and mark the angle it takes. Repeat with the other rudder and set the tie bar to lock in those angles. “It’s a game of just mess with it and see what works best,” said Critchett. “Do your sea trials to set up the steering. Once it’s dialed in, it doesn’t have to change.”

[pschauss]

Mine are toed out about 1/2” (based on tiller positions when the helm set straight ahead). I have not noticed any handling problems so I am inclined to leave them that way. Any reason why I should mess with them?

[Tony Meola]

Peter

1/2 inch is pretty much the standard. If it isn't broke don't fix it.

[Carl]

This must be the weekend for everyone noticing one rudder is straight and the other is off.

Without changing anything...turn rudders so they are both evenly off center by the same amount. Now see how wheel looks. Measure difference center to center in front and back...1/4" to 1/2" is about right.


I've heard stories for Toed In or Out...what I found. if straight they pulsate with prop wash. In or out solves that. Some say better steering when in, others say out. For me...I know the rudders stop vibrating in bathe directions and found no real difference other than that.