Rudder Alignment Question

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Rudder Alignment Question

Postby carl » Tue Mar 28, 2017 3:51 pm

Rudder Alignment Question:

I have a question regarding rudder alignment. The rudders on my 1990 32’ Fly Bridge Salon are inboard of the propellers. The two shafts penetrate the hull inboard closer to the keel line. They are not in line with the propeller shaft center lines. I read somewhere on this forum this is by design so that the shafts could be pulled out and removed without having to disturb the rudders and this makes sense, perhaps it’s even common for twin screw boats for the rudders to be a little inboard. I have ever only owned single screw inboard boats and my rudders were always in line with the propeller shaft center line.
When I set about measuring my rudder linkage prior to removing it for refurbishment I found that the rudders/tiller arms were out of alignment. They were both angled inward opposing one another. This adjustment is made through the rudder linkage and its turnbuckle function. I’m certain a previous owner had visited this linkage and didn’t get the alignment correct at reassembly.
With the two rudders being offset from the propellers centerline they are already in the inboard side of the wash or thrust of the propellers. My two rudders seemed to have been aligned forcing that wash or thrust toward the center (the keel line), but the one thing that jumped out at me is that one rudders angle inboard was even more that the other which in itself tells me a previous owner misaligned both rudders at reassembly.
Do any of you know how the two rudders should be aligned? I believe that I should be adjusting and aligning both rudders so that they are perfectly straight in the wash or thrust of the propellers when going straight forward and that there should be no angle in the rudders at all. Any angle in the rudders when going straight just doesn’t make any sense to me; actually it seems to me that any angles in the rudders would create undue stresses on the rudders.
1990 Marinette 32' Sedan Fly Bridge
Twin Crusader 350's
Chickamauga Lake, Tennessee

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Re: Rudder Alignment Question

Postby Busia » Tue Mar 28, 2017 6:15 pm

I wondered when you were going to get to this. Got all your parts cleaned up and now lets put them all together. If like mine your helm or wheel controls ( or is linked to ) one rudder, and you have a tie rod to the other rudder, this is what you do. First only worry about the rudder that is controlled by the helm. Center the wheel. ( How many turns from stop to stop? ) Center is half of that. ( do this so you can turn left or right the same amount. You don't want to be able to turn really hard one way and barely turn the other. ) Unless it is for Nascar. Put the wheel in the center of it's travel. Now don't touch it. Now the wheel thinks you are going straight. Make the rudder straight, fore and aft, or parallel to the keel. You might have a line or mark on top of the rudder shaft, or measure the rudder blade for parallel. Adjust this by adjusting the length of the steering cable. The linkage or control arm, or bellcrank on top of the rudder should be keyed to the shaft so no adjustment there. When that rudder has you going straight, adjust the tie rod length so the other rudder is parallel to the first one, so it will make you go straight too. ( just measure the distance between the rudders, at the front and the back of the blades ) If the distance is the same and nothing is bent or crooked, they are parallel. You can put a very slight amount of toe-in between the rudders like the steering on a car, but at least have them parallel. Or I'm at 907-247-2874 if you have questions---Ed
located in Ketchikan, Alaska. Gods country
32 foot Marinette express. (no fly bridge)
twin 350 Crusader (Chev 350) engines
1:1 Borg Warner velvet drive transmissions
Closed cooling (antifreeze in the engine)
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Re: Rudder Alignment Question

Postby EWRice » Tue Mar 28, 2017 8:57 pm

If your rudders are straight, it is possible that your tillers will be pointed slightly inward. Its actually a good thing. Google "Ackerman Angle". Although this is geared towards wheeled vehicles, it still pertains to twin engine boats. I see it more in high performance boats.
Muskegon Lake
1972 32' Express flybridge
Twin 318s
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1963 Thompson Super Sea Lancer
Graymarine 327
1961 Alumacraft 12'
'55 10hp Johnson

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Re: Rudder Alignment Question

Postby Fastjeff » Wed Mar 29, 2017 5:53 am

I've been told that you need about an 1/8 inch toe IN. Set mine up that way and the boat worked fine.

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