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Old 11-30-2017, 09:31 PM   #1
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Question Mainship Pilot 34 Vibration Problem

I am interested in purchasing a 2001 Mainship Pilot 34 with a single Yanmar 6LYA-STE 350HP turbo diesel engine. Today, while doing the sea trial I noticed an in and out vibration that began around 2200 RPM's and worsened when the RPM's were increased. The engine maxed out WOT at 3550 RPM's. The owner (the 2nd owner and has had the boat for 3 years) said he had the prop checked 3 months ago, when it was gauged, balanced and repainted. The shaft is true and there was no wear on the cutlass bearing. And yes, I have heard rumors this is a known problem with the Pilot 34!
When the boat was short hauled for survey, the prop (clean w/o any damage) was ID'd as a 25x28 w/4 blades. The clearance from the prop tips to the tunnel was slightly over 2" and there was some paint wearing in the tunnel over the props. My thought is the prop is over sized, but I would welcome any feedback from anyone who may have knowledge of this issue . . . Better yet, a solution would be MOST WELCOME!

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Old 12-01-2017, 06:17 AM   #2
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Welcome to the forum. There are others more familiar with the specific history of this problem, as it was more or less pronounced from year to year, so I will answer in general

The concept of reduced tip clearance is to increase thrust and speed, sometimes at the cost of added vibration. The standard "rule of thumb" for tip clearance is minimum 15% of prop diameter.

What you describe with the missing paint is called "tunnel burn," and is typically considered evidence of insufficient tip clearance.

On some Mainship models there was a factory warranty fix to correct this issue. I believe it was a propeller change to 5 blade with less diameter.

This is about the Pilot 30, but the same issue is well known in some 34 models:

BoatUS - Boat Reviews - Mainship Pilotâ„¢ 30

This is a thread about same in a P30

vibration at high rpm

I expect some P34 Peeps to chime in, but this is a start.

If the P34 fits your Bill for what you are looking for in a boat, if it was my decision I would not let this be a deal breaker as its "fixable." The Pilot 34 is a great value and IMHO for what its designed to do a great boat.

Originally Posted by Keuka View Post
And yes, I have heard rumors this is a known problem with the Pilot 34!
The clearance from the prop tips to the tunnel was slightly over 2" and there was some paint wearing in the tunnel over the props. My thought is the prop is over sized,

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Old 12-01-2017, 06:21 AM   #3
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My 2003 Pilot 34 has a little of this problem. It is unnoticeable if the bottom is clean but worsens with a dirty bottom.

I would check the normal prop vibration issues:

1. Prop trueness- your surveyor should have held a straight edge in place and rotated the prop to see any lack of true.
2. Prop shaft straight- rotate with a dial indicator at several points along the shaft
3. Prop seated properly on taper- would have to pull prop to do
4. Coupling square to shaft- check as part of 5. Open the coupling and rotate tanny and prop shaft with a dial indicator on the faces.
5. Engine alignment

One or more of these could be causing your vibration. If all are good then this boat may be more prone to the hydraulic/dynamic vibration problem. Some report success with fairing deadwood. It didn't make any difference on mine.

Good luck.

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Old 12-01-2017, 07:58 AM   #4
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Might worn engine mounts also be an issue?
Buffalo Bluff Light 28
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Old 12-01-2017, 07:36 PM   #5
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I have dealt with mystery vibration problems that proved to be bent coupling faces, especially on the transmission side after Having work done off the vessel.
The coupling half is often the lowest point on a drop output transmission, so consequently hits the ground first when mishandled.
I would inspect the entire power train very carefully before investing in a new prop.
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Old 11-18-2018, 03:59 PM   #6
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How do I access the fuel tank in the Mainship 34 in order to polish the fuel?

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