boat pulling to port when using motor!! Distress!

[kerk fisher]

This year, for the first time, our boat pulls to port pretty drastically when the motor is on. When moving slowly we don't feel it but as we pick up speed we need to need to struggle to keep it going straight.  Does not happen while under sail.  There was no trauma to the rudder, and we have a new stainless shaft. Propeller good.  Visual inspection down below indicated no problem apparently with steering mechanism, gears, all tight, running freely. Yard put boat to bed very well.  Last year no problem at all. But this year..... What happened and is happening?

[mregan]

Mine does that all the time.  I think it has to do with the water flowing by the rudder.  I think it's pretty typical

[Clay Greene]

Prop walk in forward should cause the boat to turn to port slightly but it should be more noticeable at low speeds rather than high speeds.  Once you get water flowing over the rudder, your rudder control should make the prop walk disappear.  That is inconsistent with what you are reporting, more pull to port as boat speed increases.  And the amount of prop walk wouldn't change from year to year unless something changed with the prop, which is my suspicion.  What type of prop do you have? 

[Jim Hardesty]

I think you are talking about "prop-walk".  Shamrock has a noticeable pull to port in reverse, less noticeable to starbord in forward.  When enough water starts flowing over the rudder ie a bit of speed, the prop-walk is much less.  If the boat is taken out of gear, the prop-walk stops.  So can backup about straight by taking the boat in then out of gear as soon as getting a little way on.  The only things that I can think of that would change how much prop-walk a boat gets are.  Changing the prop or repitching the prop, more pitch more walk.  Engine idle speed, higher more, lower less.
Does that sound like what you have?  If so it's normal.  If the wheel always needs to be turned to keep the boat straight when motoring and not sailing it's something else.  And to be noticeable think that it would more than a little.  When the boat gets lifted check rudder play, the cutless bearing and the cutless bearing support.
Hope it's nothing or something minor. And this helped.
Jim

[kerk fisher]

Thanks for your responses. We have the usual prop walk in reverse.  But this problem is in forward.  The prop is three blade; the shaft and cutless bearing were replaced a couple of years ago.  I'll be at the boat in a couple of weeks and can check the prop, etc more carefully but I know that the boat was motoring fine at the end of last season and this started right at the beginning of this season.  What could have happened?  And this is MORE than a little.  The autohelm will not hold because of this, so I"ve used a rope to keep the wheel straight!!

[prh77]

Could the rudder shaft have been bent during haul/launch? Sounds like a trim problem as we say in aviation.

[Jim Hardesty]

To the bent rudder shaft, I would suggest that may be the shaft strut got damaged or bent at lift/out or lift/in.

If this happened just after the shaft and cutless bearing were replaced thats where I'd start looking first. If so my guess is the shaft is out of alignment, a lot.  A few of things that I can think of are,  a bent or broken shaft strut,  broken or loose engine mounts,  and bad engine alignment.   All should have been checked when the shaft and cutless bearing were replaced.

You didn't mention any vibration.  Do you have any?
   
With having to use a rope to keep the boat straight.  This is not something that I would live with and continue to use the boat till I found the cause.

Jim

[Clay Greene]

Don't think it could be the rudder or the steering system if it is not happening under sail.  It would have to be the propeller shaft, the strut or the propeller.  Interesting in that you say you haven't noticed an increase in the prop walk in reverse - I would think that whatever is causing the port pull of the bow in forward would increase the port pull of the stern in reverse. 

I'll be interested to hear the answer when you figure it out - it's a puzzler. 

[scotty]

It seems significant that this happens when the speed is increased.  Something is tweeking out of line.  It sounds like you should get on this ASAP (it could get worse).  I agree with Jim that this is not something you should have to live with.

[Ron Hill]

Kerk : Not too sure as what to advise??  If your shaft were out of alignment the vibration would be VERY evident.  Take a look at the play between the rudder and the locked wheel.  

Bothers me that the Autohelm will not hold it and it's something that just happened this year!?!

Check that rudder play and let us know.  

[Jim Hardesty]

Kerk,
Pardon me for treating your real and potentially serious problem as a bit of a "brain teaser".   After some thought my idea about shaft alignment and/or strut problems doesn't' hold up for two reasons.  First, the vibration would be bad.   Second, many if not most boats are built with the shaft at an angle, helps with prop-walk and shaft removal.  The steering has little or no pull.
So,  another thought is rudder delamination.  With the propwash the delamination opens up and changes the rudder shape and it pulls.  More RPM more pull.  At sailing speed with no prop wash the delamination isn't opening, at least not as much, and isn't noticeable.  Does that sound like what's going on?
Just my thoughts, the problem may be evident  and a fix started when the boat is lifted for winter storage.  Please let us know.
Jim

[Roc]

What you're seeing is "prop walk" in forward, which is typical.  In reverse, prop spins counterclockwise.  The blades bite into the water and will pull the stern to port.  Typical for a 3-blade prop. In forward, prop spins clockwise.  Again blades bite in, but this time it pushes the stern to starboard (pointing the bow to port).  My boat does the same thing. 

[patrice]

Hi,

Just to let you know that I have the same issue, but mine is a very easy fix.
It happen because I pull my dinghy attaching the line to the port cleat.
If I run the line thru the walk thru then to the cleat, it is a lot less pull, since line is more centered to the boat line.

I know sound funny, but I checked it by changing side, attach to starboard cleat, boat pull the other side.

[lazybone]

I would never think it was impossible that lazy yard workers could have bent your rudder to one side or the other in order to remove and replace your new prop shaft.  Or they could have loosened the cutless strut and shifted that in order for the shaft replacement to clear the rudder.
They might have thought either of those was preferable to removing the rudder.

Good yard help is hard to find.

[Roc]

Based on what Kerk describes, it sounds like it's more than the usual prop walk.  Aldo made some good points about the yard being sloppy in their work.  If the boat is out of the water (or when it does come out), I would check to see if everything looks to be aligned (strut, shaft, etc.).  Also check the rudder, and put the wheel at the center mark and see if the rudder is also centered when you do that.  Maybe you think when the wheel is centered, your rudder is also, but maybe something has changed (cables?), so they don't line up anymore.