Reply
 
Thread Tools Display Modes
 
Old 06-27-2016, 01:16 PM   #1
Senior Member
 
City: southern California
Country: USA
Join Date: Jul 2015
Posts: 141
New prop and shaft.

Our surveyor noted some small corrosion spots on the shaft, and wanted to pull it for a dye penetrant test. Since the boat is a single, and I plan to be outside of tow range (insurance wise anyway) I thought I'd err on the side of caution and replace it during my haul out. Good thing.

Here's what it looks like where we couldn't see it...
Click image for larger version

Name:	ImageUploadedByTrawler Forum1467047449.538200.jpg
Views:	93
Size:	26.8 KB
ID:	53555Click image for larger version

Name:	ImageUploadedByTrawler Forum1467047464.985037.jpg
Views:	83
Size:	27.0 KB
ID:	53556
That big pit on the photo is well over an eighth of an inch deep.

Of course, I have to get a new prop as well, since the shaft was a crazy custom taper. I've been researching the three vs. four blades idea. The boat previously topped out at about 8 knots, but I felt it was under propped with the existing 4 blade. Most of the Google and search hits are for boats much faster than mine. Any trawler owners have experience in changing props on slower boats?
__________________
Advertisement

questionmark is offline   Reply With Quote
Old 06-27-2016, 02:59 PM   #2
Guru
 
djmarchand's Avatar
 
City: East Greenwich, RI
Country: USA
Vessel Name: Bella
Vessel Model: Mainship Pilot 34
Join Date: Aug 2012
Posts: 2,875
Here we go, another over propping thread!!!

But seriously, an eighth of an inch is bad, so you are right to replace it. Take accurate phototached rpm measurements at wot and work with a good prop shop. As Ski said recently, prop selection is part science and part art with a bit of luck thrown into the mix.

David
__________________

djmarchand is online now   Reply With Quote
Old 06-28-2016, 07:12 AM   #3
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,515
The best hope of changing/improving a prop is done by using a good tach and a GPS to create a graph of RPM / boat speed.

Every 200 RPM should make a smooth graph.

IF you do change the shaft and prop, be sure to specify a std taper so you can change props in the future, and carry a spare..
FF is offline   Reply With Quote
Old 06-28-2016, 08:44 AM   #4
Guru
 
O C Diver's Avatar
 
City: Fort Myers, FL... Summers in Crisfield, MD
Country: USA
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 4,806
Quote:
Originally Posted by questionmark View Post
The boat previously topped out at about 8 knots, but I felt it was under propped with the existing 4 blade. Most of the Google and search hits are for boats much faster than mine. Any trawler owners have experience in changing props on slower boats?
Are you referring to other boats of the same make and model with the same engine? Hull shape and engine HP have a great deal to do with speed. As an example: my boat cruises at 7 knots. To reach 9 knots would require more than 4 times the HP at 7 knots.

Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
O C Diver is online now   Reply With Quote
Old 06-28-2016, 12:14 PM   #5
Guru
 
jleonard's Avatar
 
Join Date: Jun 2008
Posts: 2,735
Quote:
The boat previously topped out at about 8 knots, but I felt it was under propped with the existing 4 blade. Most of the Google and search hits are for boats much faster than mine. Any trawler owners have experience in changing props on slower boats?
I always thought mine was "underpropped" but I get full rpm at WOT with a calibrated tachometer, and when I compare to other boats of the same make and model I am about the same speed and fuel consumption as them.
Even though I only top out at about 8.3 knots.
__________________
Jay Leonard
Attitude Adjustment
40 Albin
Mystic,Ct
jleonard is offline   Reply With Quote
Reply

Thread Tools
Display Modes

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





All times are GMT -5. The time now is 07:17 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012