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Old 21-11-2012, 03:38   #1
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Shaft out of balance? - saildrive

Hi !

I would greatly appreciate some help from the experts here.... Ive rung around a few boat yards but cant get any straight answers to my problem.....

I fouled my prop with some heavy rope recently, causing the prop to stop, and shear off the end of the sail drive shaft! (Bukh DV8 SME w/ sail drive)

I lost the prop, but got a old spare put back on what was left of the old shaft as a temporary fix. It has been working well, however there is a noticable vibration when underway, that I am guessing is the shaft being out of balance (or even bent slightly). The vibration seems to come though the hull/fittings, is not major but is noticable to me and people who know the boat. It does not appear to effect the engine on its mounts.

Im not 100% its the shaft, and im not 100% certain that there isnt other internal damage due to the fouling.

As I see if, I have 4 options....

1) Replace the shaft. (new shaft is $1600 !!!! plus how many hrs labour ?)

2) Replace the whole sail drive with a reco unit (reco unit is $2000 plus how many hrs labour ??)

3) Do nothing and see what happens !

I would really appreciate your thoughts.... particularly on how big a job options 1 & 2 are.

Thanks !!
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Old 21-11-2012, 03:51   #2
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Re: Shaft out of balance? - saildrive

Before you replace the shaft, take it to a shop that specializes in balancing shafts (there's one here in Southern California (Wilmington) that our shipyard uses. They'll figure out if it's unbalanced or not straight and what you can do about it. Hope your yard can steer you to one.

Hope this gives you an idea and you have a similar place near you:

http://www.wilmingtonironworks.com/propellershafts.html
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Old 21-11-2012, 12:04   #3
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Re: Shaft out of balance? - saildrive

Find a good tech who has training and experience with your specific sail drive. SD's are complicated and proprietary so there is no substitute for experience.
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Old 21-11-2012, 13:48   #4
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Re: Shaft out of balance? - saildrive

I would suspect the old prop being out of balance before anything else. If the short shaft in the saildrive was bent, you would have had a hell of a time getting it to fit.
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Old 21-11-2012, 13:56   #5
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Re: Shaft out of balance? - saildrive

I vote for the sail drive to be inspected as well. The fouling of the prop may have "coined" a bearing race in the lower. That could account for the minor vibration. I would think that would be a remote possibility, but could turn into a major repair in the future.

The prop balance could be a problem as well. The only way to find that, would be to swap props. The problem being here is the money spent on another prop, and that being a waste due to it not fixing the problem.

A bent shaft could also cause the vibration, but could be hard to determine without a dial indicator. Easy enough if you can find someone with a dial indicator and your on the hard. A bent shaft is also a long term problem if that is the situation.

Any other causes at this point would be wild speculation. Best to contact a reliable person to look at the sail drive. Could save money over time.

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Old 21-11-2012, 13:57   #6
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Re: Shaft out of balance? - saildrive

Chances are the shaft is bent from the rope fouling. Clamp a dial indicater on the leg and measure the runout. If it is .005 or less it should be ok.
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Old 21-11-2012, 17:03   #7
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Re: Shaft out of balance? - saildrive

Thanks so much for the great replies....

Unfortunately I haven't been able to find anyone locally who knows anything specific about Bukh saildrives. There is one local Bukh rep, but for various reasons I cant (wont!) deal with him. So im left with my reliable diesel mechanic and the collective wisdom of this forum !. To be honest, Ive found the information Ive received previously on this forum much better than any of the "professionals" locally.

My other issue is access to slipping/hard stand. Slipping costs here are painful, and a three days on the hard to pull pulling bits out fiddle about will cost $1000 straight up. Then once I find out whats wrong, there is the lead time to order parts etc (which usually have to come from overseas), which will require an additional haul out.

Even just to swap props (which I hadnt really considered - thankyou!) will be a $500-700 job.

Ideally, Id like to take an educated guess at what is wrong, over engineer the solution (just in case!) and have it all ready to go so I can have it slipped and fixed in one or two days.

Can anyone take a stab at how much labour is required to replace the entine SD unit ? Does the engine need to come out ? Or can the SD be dropped out the bottom through the hull ?

Thanks !
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Old 02-12-2012, 23:18   #8
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Re: Shaft out of balance? - saildrive

Just to bump this back to the top......

Ive had two totally conflicting opinions from local mechanics on this one....

Does anyone know if the Bukh sail drive unit can be replaced simply by 'dropping' it through the hull with the engine in situ (on the hard) ?

One guy told me "easy job - few hours" and another told me "engine needs to come off mounts, big job, 20+ hours labour"

Any thoughts ?!?

Thankyou !!
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Old 03-12-2012, 05:01   #9
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Re: Shaft out of balance? - saildrive

I don't know anything about the Bukh, but on the Volvo and Yanmar saildrives, the prop shaft is only ~6" long, is ~1" diameter and supported on both ends by heavy bearings. If the Bukh is similar, it is doubtful that you bent that shaft.

On the Yanmar and Volvo drives, removing/replacing is very easy. The engine mounts will probably need to be unbolted from the stringers and the engine moved forward a couple of inches to get clearance from the driveshaft. This takes ~5 minutes to do and another 5 minutes back on when done.

I agree with the first guy. If I was doing this job, it would be a few hours. You won't be dropping it through the hull - but rather pulling it up into the boat. Still easy to do unless you have no room in the engine room to work in.

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Old 03-12-2012, 05:17   #10
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Re: Shaft out of balance? - saildrive

Thanks colemj,

I should clarify... after inspecting the shaft when I last got the boat out of the water, the shaft has sheared where the prop was attached (rather than bent).

I amagine the vibrations are as a result of the shaft spinning around with mot of its 'weight' at the tip all over on one side.
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Old 03-12-2012, 06:58   #11
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Re: Shaft out of balance? - saildrive

If the shaft was sheared, then you need a new shaft regardless of it being bent or not. If the shaft really cost almost the same as a drive, then get the new drive. Good luck.

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Old 03-12-2012, 08:52   #12
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Re: Shaft out of balance? - saildrive

Id get a new sail drive, it goes in from the top, but the engine may need moving

why not email Bukh UK . Ive always found them good, they ship parts worldwide too,

or go directly to Bukh in Denmark, bukh@bukh.dk and ask them

Dave
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