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Old 01-11-2012, 10:23   #1
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Mystery!

On next Tuesday I will know the answer but I'm wondering what you think.

I bought a Grampian Classic 31 about two months ago - older glass boat. Was surveyed recently and everything checked out. I sailed it 6 or 8 times in September and powered her on and off moorings and into and out of the slip. Its a full keel with the rudder hung off keel and prop in an aperture. It handled as I would expect. Now, the last two times I've moved it under power, it has an uncontrolable tentancy to go to starboard as soon as I put it in forward - doesn't matter if engine is just ticking over of if I give it a shot. Engine is almost new Volvo. I haven't seen the boat out of the water yet but I'm eager to see the hull next week.

Any thoughts on what the problem might be?

Phil
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Old 01-11-2012, 10:36   #2
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Re: Mystery!

I believe it's 'prop walk'. W/o going into a lot of detail, go here Prop Walk
It's a common event for 3 blade fixed props.
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Old 01-11-2012, 10:37   #3
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Re: Mystery!

First thought is....rudder.
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Old 01-11-2012, 10:42   #4
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Re: Mystery!

Quote:
Originally Posted by Atlantic Salt View Post
On next Tuesday I will know the answer but I'm wondering what you think.

I bought a Grampian Classic 31 about two months ago - older glass boat. Was surveyed recently and everything checked out. I sailed it 6 or 8 times in September and powered her on and off moorings and into and out of the slip. Its a full keel with the rudder hung off keel and prop in an aperture. It handled as I would expect. Now, the last two times I've moved it under power, it has an uncontrolable tentancy to go to starboard as soon as I put it in forward - doesn't matter if engine is just ticking over of if I give it a shot. Engine is almost new Volvo. I haven't seen the boat out of the water yet but I'm eager to see the hull next week.

Any thoughts on what the problem might be?

Phil
Phil,

Unfortunately the possibility list is quite long.

First the growth on your prop would be where I would start. There could be a bent rudder, bent keel, loose rudder. All of these are possible, but probably unlikely.

I would think growth on the prop being the possible culprit, but it's only an idea right now. The more growth (hard growth) on the prop, the more likely the craft to have prop walk.

Does the stern tend to come around, or does the boat steer in that direction? There is a difference, and is usually quite noticeable.

How does she act when in reverse?

Unfortunately until she is hauled out, none of our opinions make much difference.

I know that doesn't help, but the list can be quite random.

James L
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Old 01-11-2012, 13:09   #5
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Re: Mystery!

Uncontrollable tendency meaning you can't steer?

I know these are basic but is there a tidal current running at the time? Is there a lot of wind on the bow? Are you certain your rudder is straight when you go forward? If you have wheel steering then the indicater might be a bit off.

Prop walk usually is more pronounced when backing but as was said with a large 3 blade you'll get it going forward too. Prop fouling will make it more pronounced.

Good luck in finding the culprit and please let us know what you determine it to be.

kind regards,
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Old 01-11-2012, 14:39   #6
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Re: Mystery!

These are all good ideas and most are things that I had considered. What really puzzles me is that for a month I did not have this issue - now I do. I think that, as has been said, I'll have to wait until I get it out of the water to see just what the problem is.

I will be sure to post the "answer" next week so be sure to come back to this!

Phil
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Old 01-11-2012, 14:56   #7
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Re: Mystery!

The suddeness is what made me think "rudder". How was she moored before you noticed the difference? Could something have hit it?
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Old 01-11-2012, 14:59   #8
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Re: Mystery!

My guess would be a problem with one of the rudder pintles, maybe your recent use knocked a lump of rust off that is only a factor when the prop wash hits the rudder, not simply when underway (under sail).

Yeah, let us know the answer!
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Old 01-11-2012, 15:20   #9
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Re: Mystery!

I don't "think" it could have been hit. Remember the rudder is hung off the keel - not a split keel/rudder arrangement. I know that it wasn't hit when I was using it.

I like the pintle idea. I was thinking that perhaps the rudder was loose on the stock so that when there was a lot of prop wash it rendered the rudder useless.

We'll see next week - but a good mystery!

Phil
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Old 01-11-2012, 15:41   #10
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Re: Mystery!

It tends to be especially bad on boats with the prop in a rudder aperture. The more tip clearance the better. If someone has put a prop that is too close to the aperture edges then it will be worse.
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Old 07-11-2012, 10:54   #11
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Well I hauled the boat yesterday and what did I find..... Good news is that nothing that requires repair - only cleaning up.

First the prop itself was 3 blade and that would make more wall than 2 blade as was said. Then the prop was very encrusted and much distorted by barnicles , etc. there was also a large clump attached to the lock nut - about size of grapefruit so it was further distorted. Them there was a big patched growth on starboard side just I n front of prop and the right side of rudder was more encrusted than port side.

I think all these things conspired to create the severe turn to starboard whenin gear. I think it started to be really bad after the boat sat in marina slip for several weeks with starboard side facing sun - thus more growth.

I have cleaned off a the hull and most of prop but complete cleaning may require me to remove prop. Unfortunately. Will have to wait for spring to confirm that issue is resolved (I'm in Canada) but I am confident.

Thanks to all for the suggestions - it was fun.

Phil
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Old 07-11-2012, 12:18   #12
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Re: Mystery!

Cheers for the follow up - fingers crossed that is the case.
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Old 07-11-2012, 12:21   #13
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Re: Mystery!

Glad there were no major problems.

Sounds like you may have some major chiseling or scrubbing to get the problem resolved, but no major expense.

Thanks for the follow up,

James L
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Old 07-11-2012, 12:34   #14
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Re: Mystery!

I'm a bit puzzled as to why you wouldn't just get a diver to check and clean the bottom, for a fraction of the cost of a haulout. That's what divers are for!

Best plan now is to get the bottom looked at again in a few months, and if you have major growth again you will know that your bottom paint is no longer effective.
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Old 07-11-2012, 16:19   #15
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Re: Mystery!

Just a note on the diver and check again issue. I'm in Atlantic Canada and the boat is out of the water for winter - won't be in again until May. There is NO cost for the haulout as it is included in the club dues. It also includes 2 other haulouts during the season so I will be sure to do that just to keep an eye on it.

Thanks

Phil
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