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Old 03-21-2013, 06:57 PM   #1
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Question rudder angle on single screw

I have a 34 mainship pilot single engine. I have had trouble turning at slow speed. I found the rudder turns further to the port than to the stbd. Is this standard practice for this boat?? Boat tracks straight when auto pilot is showing 0 degrees. This is my first single screw boat. Thanks for any help.
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Old 03-21-2013, 07:17 PM   #2
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Well, the rudder shouldn't move more in one direction than the other but a single screw boat may turn a tighter turn in one direction than the other because of prop walk.

Propeller walk - Wikipedia, the free encyclopedia

Have you actually measured the rudder angle or are you relying on an indicator?

I suggest reading Chapmans Piloting or a good book on single screw boat handling to learn what to expect from your boat. It's not at all like driving a car or like operating an outboard or I/O powered boat.
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Old 03-21-2013, 07:24 PM   #3
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Depending on the type of actuator involved, you may be able to adjust the imbalance out. No it is not normal. It should be 35 degrees each way (total 70) some very special types of rudders use more or less range but 35 is normal.
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Old 03-21-2013, 07:25 PM   #4
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For a balanced rudder the maximum rudder angle should not exeed 45į from max. strbd. to max. prtsd.
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Old 03-21-2013, 07:37 PM   #5
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Originally Posted by 717fitz View Post
I found the rudder turns further to the port than to the stbd. .
I'm wondering if you mean the boat turns faster to port than to starboard. It's important that you define the problem correctly.( As rwidman pointed out.) This may very well have a simple explanation.
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Old 03-21-2013, 08:25 PM   #6
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Many other Willard owners complain about poor rudder performance w 35 degrees deflection. My rudder swings 90 degrees (45 each way) and I have no complaints at all. The faster the boat the less full deflection untill you get to planing and then 35 degrees is standard. But for slower boats w big rudders more deflection seems best up to at least 45 degrees on FD hulls. Sometimes I use full deflection running in following seas quartering and am grateful for the extra control.
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Old 03-21-2013, 08:57 PM   #7
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Well, the rudder shouldn't move more in one direction than the other but a single screw boat may turn a tighter turn in one direction than the other because of prop walk.

Propeller walk - Wikipedia, the free encyclopedia

Have you actually measured the rudder angle or are you relying on an indicator?

I suggest reading Chapmans Piloting or a good book on single screw boat handling to learn what to expect from your boat. It's not at all like driving a car or like operating an outboard or I/O powered boat.

I have measured the rudder arm movement. Total swing at steering arm is 7" with 3.5" to port and 2.5" stbd measured from center. Raymarine auto reads 30deg to port and 20 deg to stbd. Only adjustment would be to move the hydro cly,which is screwed down. Thanks for your help
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Old 03-21-2013, 09:03 PM   #8
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About a year after purchase of the current boat, had an opportunity to replace the rudder arm and set it up to 45 degrees instead of the former 35 degrees. This also required relocating the base of the hydraulic cylinder, although this might not be needed for other boats/applications.

A very noticeable improvement in close quarters handling. As Eric says, "no complaints at all."

As an aside, I have had some experience with rudders with flaps, rudders that will go to 60 degrees, and Shilling rudders that usually go to around 70 degrees. All of them are designed to greatly improve close quarters maneuvering at slower speeds.
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Old 03-21-2013, 09:14 PM   #9
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Originally Posted by 717fitz View Post
I have measured the rudder arm movement. Total swing at steering arm is 7" with 3.5" to port and 2.5" stbd measured from center. Raymarine auto reads 30deg to port and 20 deg to stbd. Only adjustment would be to move the hydro cly,which is screwed down. Thanks for your help
There's something wrong there, the question is how did it get that way? A poor repair by a previous owner? Incorrect installation of the cylinder?

And then of course, how to correct it.

There's an arm from the cylinder to the rudder post, right? Could it have slipped on the rudder post?
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Old 03-21-2013, 09:29 PM   #10
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There does not seem to be any damage in the rudder post, arm or cylinder. No extra holes where cylinder bolts to rudder post support. History from previous owner did not show any past work done in this area. Problem has been with boat since I have had it. To make a hard port turn, I must use thruster. Stbd turn is ok.
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Old 03-21-2013, 09:37 PM   #11
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Repositioning the cylinder is not a big deal. I wouldn't be surprised to find that the ram was installed in the wrong position right at the factory That would be one of the more minor factory errors.
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Old 03-21-2013, 09:58 PM   #12
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Thanks to all. I will recheck my findings and look into reposition of cylinder. Y'all did a great job of answering my question which was should the rudder swing equally on a single screw boat. Thanks to all. This was my first time on Trawler Forum.
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Old 03-21-2013, 10:38 PM   #13
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Rudders should never turn more than 35 degrees.

More than that you risk damaging the steering gear.

Your problem is the rudder is too small. It should equal 3 percent of the underwater profile of the hull.

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Old 03-21-2013, 10:51 PM   #14
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The 35 degree rule is due to hydrodynamic stalling and loss of efficiency.

The reality is though that you can use an increase in rudder angle greater than 35 degrees as the stern starts to swing the dynamic angle of the rudder relative to the water likely won't exceed 35 degrees. Mines around 42 degrees.

Now if you want to talk loading and rudder size, the Nordic Boat Standard, part C7 has some great calculations to determine rudder forces and equipment .
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Old 03-21-2013, 10:56 PM   #15
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Sceptic says;

"Rudders should never turn more than 35 degrees.

More than that you risk damaging the steering gear."

Been through all kinds of weather for 7 years and no problem whatsoever.
There is one safety consideration though. When backing fairly fast one needs to keep a firm grip on the helm so as not to let rudder flop over to full deflection. Damage could result this way. I know of few people that back that fast though and it's relatively easy to hold the rudder to about 20 degrees deflection. If one backs at a walking pace there's no problem but if you back at 3 or 4 knots things can get out of hand.

There is no other negative consideration for rudders at 45 degrees on a full disp boat or similar speed semi disp boat.
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Old 03-22-2013, 12:06 AM   #16
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717fitz: There has to be some sort of locking arrangement between the rudder arm and the rudder post, usually a key. If all you have is a clamp type attachment, it may be that the arm has slipped, but I think that this would be very unusual. It could be that it has been like this for years, even from the beginning, and may not have been noticeable if the thruster was used often.

Northern Spy says: "The 35 degree rule is due to hydrodynamic stalling and loss of efficiency." This is what I have been exposed to for years. Spot On!

Eric says: "There is one safety consideration though. When backing fairly fast one needs to keep a firm grip on the helm so as not to let rudder flop over to full deflection. Damage could result this way. I know of few people that back that fast though and it's relatively easy to hold the rudder to about 20 degrees deflection. If one backs at a walking pace there's no problem but if you back at 3 or 4 knots things can get out of hand." Manual steering system Eric?
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Old 03-22-2013, 12:31 AM   #17
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717fitz:
Northern Spy says: "The 35 degree rule is due to hydrodynamic stalling and loss of efficiency." This is what I have been exposed to for years. Spot On!
I, too, have been exposed to this theory. (35 degrees off dead center.) I've been told by some pretty savvy captains that the rudder actually "stalls" when positioned over 35 degrees to the directional flow of the water. Not so noticeable in slow boats but it happens nevertheless.

Note: Stalls, meaning that it starts to lose it's efficiency.
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Old 03-22-2013, 07:34 AM   #18
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Your problem is the rudder is too small. .........
No. From his description, there is more deflection to one side than to the other. It should be the same. That is his problem.

Once this is corrected, it there's still a problem, he can examine the total deflection angle or the rudder size,
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Old 03-22-2013, 07:36 AM   #19
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717fitz: There has to be some sort of locking arrangement between the rudder arm and the rudder post, usually a key. If all you have is a clamp type attachment, it may be that the arm has slipped, ......................
That would be the first thing to check. Perhaps the key is missing and the clamp has slipped.
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Old 03-22-2013, 11:07 AM   #20
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Jay N asked;

"Manual steering system Eric?"

I installed an oversized hydraulic system 7 years ago. The cable system was harder to control while backing fast but still manageable. One just needs to be aware and in control while backing fast. And most boaters don't back fast at all. Willy's stern so resembles her bow that she can be backed really fast.

I've been well aware of the 35 degree standard but most of us have operated a small sailboat w hanging rudder on the transom and a tiller. And most of you will recall that those rudders are very effective way beyond 35 degrees deflection. Perhaps I'd gain even more using 55 degrees but at 45 degrees I've got all the rudder response I need. Re the rudder degree question I'd not go over 35 degrees w John Baker's boat and 55 degrees may be fine and very effective on a sailboat.

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