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alignment specs and vibration

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bobct

Advanced Contributor
I have a vibration over 2,000 RPM's. Alignment was done last year and felt great until the end of the season. I had my props tuned but nothing else done.

I have a mechanic coming to help me check the alignment tomorrow night but I unbolted the coupling to get a jump on things. I know we did it in the water to .003 about mid season last year. I'm getting .006 on the bottom. Is that a mile in alignment terms? I know it's twice the spec so maybe I answered my own question.

Are you guys doing alignments every year? I guess my bigger question is what caused it to change, assuming he validates my findings.

I dove under on Sat and didn't seen anything on the prop. I'm pretty sure I installed the prop correctly but that'll be my next check if the alignment doesn't fix things.

This happens to be the same engine I just installed the new thermostat so I'm also keeping a cyl misfire in the back of my mind. It sure feels like a vibration but I guess a misfire might feel the same.

Bob
 
Bob,

I think that is a good question that someone will have a definitive answer for. I can say this....while we have had two conditions on the boat over the years with alignment...NOTHING solved our vibration issues like propscan. Our props were so far out it was as if they were installed AFTER they were kicked across the warehouse floor several times. Even though our alignment was off and our cutless bearings were worn, the biggest improvement was in balancing the props. Since the last propscan, we had gotten three seasons out of that scan
 
Al, that's what I meant by "tuned", I did have them propscanned over the winter. That's in the back of my mind, maybe they did one wrong?

Last week was the first I was able to run it over 2,000 and felt it. I guess we'll rule in/out the alignment tonight and go from there. (Cutless bearing is new along with the shaft and all tested last year).

Bob
 
No more than .003 IMO. Check all engine/tranny mounts to ensure they are tightened down properly. When alignment was done last year, was the boat in the water for a while?
 
My mechanic came by and helped me check the alignment on the port engine. He thought there was some runout on either the trans or shaft flange but he rotated 180 degrees and it seemed ok. He thought it was odd but he did it a couple of times, was at .003. We didn't do any engine adjustment, bolted it up and took it for a spin.

It was better, or maybe I was talking myself into it when he asked me if anything had changed with the rudders. That's when the light when off. I aligned my rudders a few months ago after I found the diagram and spec in my manual. He's 80% sure it's my problem.

Right now, they're very slightly towed "out". I can see the top of my rudders because I have a gap between the edge of my swim platform and the transom. Would you increase the tow out or pull them in? It might be trial and error but this is an easy fix if it works.

Bob
 
Just wondering! Am I correct in assuming that the toe of the rudders would be the leading edge (our toes are in the front of our feet) which is just about equal to the rudder shaft? So a toe-out condition would mean that distance from toe-to-toe is greater than the distance of the trailing edges of the rudders which are pulled in some?

Thanks,
Erich
 
Bob:

what is the spec you found and in which manual?

we set the rudders to be toed IN as well....about 1/16th if I remember correctly.

As far as the alignment, you answered you own Q - 0.006" is twice as far out as what is deemed acceptable. depending upon the hull and the running gear installation, you may be able to tolerate more. Setting the coupler to within 0.003" will eliminate any tolerance issue. As far as alignment shifting, if you haven't hit anything, I'd suspect the motor mounts are worn out. I dismantled one of my old ones and it was broke internally. since changing them, no alignment issue have recurred.
 
Mark,

Here's what I found in my boat manual:


"With the rudders in the dead ahead position, the trailing edge of the rudder blade must toe out 1.5 degrees and the tie bar between the two rudders should be set so that the forward end of the arm is toed in at 10 degrees"

The part I don't understand is the 10 degree measurement. The tiller arms are keyed onto the rudder shafts so there's no adjustment possible. I have a tie rod/lock nut on each end of the tie bar so I can move the rudder blades in/out.

I can just see the tops of each rudder through my swim platform so I might have to do some trial and error until I get it right. I'm hoping the vibration gets better or worse so I know I'm onto something. We wound up not making any changes to the engine alignment after all so I think they're ok. I might start replacing them on each engine when I have a reason to do an alignment again.

Bob
 
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Bob,

Good luck...I have noticed that unless the changes I had made were REALLY off the wall RADICAL, the was little noticable "feel" to the adjustment, but that's me.
 
The mechanic didn't go as far as he should have. If he rotated the coupler "180 degrees" and the gap changed, that's an indication that the coupler, tranny flange or shaft is warped. That's why when checking final alignment, you rotate in 90 degree increments and check numbers each time. The numbers should remain the same.
 
bobct said:
Mark,

Here's what I found in my boat manual:


"With the rudders in the dead ahead position, the trailing edge of the rudder blade must toe out 1.5 degrees and the tie bar between the two rudders should be set so that the forward end of the arm is toed in at 10 degrees"

The part I don't understand is the 10 degree measurement. The tiller arms are keyed onto the rudder shafts so there's no adjustment possible. I have a tie rod/lock nut on each end of the tie bar so I can move the rudder blades in/out.

I can just see the tops of each rudder through my swim platform so I might have to do some trial and error until I get it right. I'm hoping the vibration gets better or worse so I know I'm onto something. We wound up not making any changes to the engine alignment after all so I think they're ok. I might start replacing them on each engine when I have a reason to do an alignment again.

Bob
Click to expand...

Bob,

Just following up on this old thread. Did you ever fix your vibration issue and, if so, what was the fix.

Also I don't understand how the trailing edge of the rudder blade can be toed out only 1.5 degrees (meaning a greater distance apart than the leading edge) if the tiller arms are at 10 degrees. If the tiller arms are set perpendicular to the tie bar, would the trailing edge of the rudders then be toed in, meaning that the arms are not lined up with the rudders below them? And how the heck would you figure a 1.5 degree angle? What is the difference in the distance between the leading edge and trailing edge?

Thanks,
Erich
 
My boat is single screw so the rudder issue is niether her nor there for me but reading this leads me to ask Why do they toe them out?
 
Erich,

Yes, I did and was definitely rudder related. I did a couple of things:

1) replaced the bushings where the rudder post goes through the transom to reduce the play.

2) re-aligned the rudders which made a huge difference in both feel and speed. I'm well aware of the placebo effect but that wasn't the case here :) I was basically dragging through the water since I bought the boat. I picked up 200 RPM's on the top end and it was the same smpooth feeling after you get new tires.

How do you measure 1.5 degrees across a 10' span? Not easily. I finally settled on 1/8" so it's pretty precise. Missnancy, rudder (s) need to be toed in or out a little bit so that the the prop wash doesn't cause the rudder to vibrate.

Bob
 
Bob,

I bet most of the vibration was corrected by the rudder bushings. Since the rudders as keyed, there must be a port rudder and a starboard rudder in order for the tiller arms to be set to a different angle (10*) than the rudders below them n(1.5*), a difference of 8.5 degrees according the specs you quoted. If the rudders were reversed, I imagine things would be really messed up.

Erich
 
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