Cruisers Forum

Join CruisersForum Today

Thread Tools Rate Thread Display Modes
Old 18-09-2012, 09:28   #1
Registered User

Join Date: Jul 2012
Posts: 148
Repower Vibration Concern

Recently had a Nanni 37hp replace an old 24hp on a Tartan 41. Yard has checked alignment and says it is fine, but there's still a bit more vibration than before the repower. The drive is smooth at idle up to ~1800RPM, but then begins to vibrate as RPM exceeds 2000. The shaft, stuffing box, cutlass and prop were all replaced with the new engine, However, the same diameter shaft was used.

Does anyone have rule-of-thumb info for appropriate shaft diameter & unsupported lengths for a given power out put? Maybe I worry too much. But has anyone else run into shaft size issues when repowering with higher power?
zstine is offline   Reply With Quote
Old 18-09-2012, 09:33   #2
Registered User
Dulcesuenos's Avatar

Join Date: Dec 2010
Location: Florida Keys, Bahamas Bound
Boat: 38' French Cat
Posts: 2,653
Images: 4
Does it vibrate in neutral at that rpm?
Dulcesuenos is online now   Reply With Quote
Old 18-09-2012, 09:47   #3
Senior Cruiser
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Somewhere along the US West Coast
Boat: Modified Choate 40
Posts: 10,469
Images: 122
Re: Repower Vibration Concern

Run it full bore in reverse. If no vibration, then it's the shaft diameter. In reverse it's pulling the shaft, not pushing it.

I re-powered mine a couple years ago and even went to a Pythondrive, and still ended up going to a larger shaft. A 1'' shaft, 5' long isn't really enough to push a 40' boat at hull speed. It starts to whip under the stress.
My old system had less torque but with higher RPM's. I went to a 1-1/8" shaft and it runs dead smooth now.
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful!
A nation of sheep breeds a government of wolves!

Take nothing but pictures, leave nothing but footprints!
delmarrey is offline   Reply With Quote


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 00:08.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.