Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 15-01-2012, 10:48   #1
Marine Service Provider
 
jaffadog's Avatar

Join Date: Dec 2011
Location: Deltaville, VA, USA
Boat: Sam L. Morse Bristol Channel Cutter 28 ft
Posts: 13
Does cutless bearing life vary depending on initial rubber thickness?

I am redoing my sterntube and shaft and juggling various size options. I am wondering whether the service life of the cutless bearing is at all related to how thick the rubber portion of the bearing is to begin with.

Compare these choices:

1. 1-1/2" ID sterntube; 1-1/4" shaft; effective wall thickness of the cutless bearing (brass and rubber) is 1/8"; so maybe the rubber portion of that is 1/16"

-or-

2. 1-1/2" ID sterntube; 1" shaft; effective wall thickness of the cutless bearing (brass and rubber) is 1/4"; so maybe the rubber portion of that is 1/8" or more

I'm wondering if option 1 will "wear out" more quickly than option 2. I'm inclined to think it would, because the channels for water to get into the bearing are so small, so water lubrication is less effective. And the rubber is so thin, that you don't have to lose much before you're through to brass.

Has anyone found this to be true? Or would the service lives of the bearings above be practically the same?

Thanks!
Jeremy
__________________

__________________
jaffadog is offline   Reply With Quote
Old 15-01-2012, 10:53   #2
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
Re: Does cutless bearing life vary depending on initial rubber thickness?

Cutlass bearing life is more determined by the engine/transmission alignment to the shaft and how true (correctly pitched and balanced) the propeller is.
__________________

__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 15-01-2012, 11:03   #3
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
Re: Does cutless bearing life vary depending on initial rubber thickness?

Quote:
Originally Posted by jaffadog View Post
I am redoing my sterntube and shaft and juggling various size options. I am wondering whether the service life of the cutless bearing is at all related to how thick the rubber portion of the bearing is to begin with.

Compare these choices:

1. 1-1/2" ID sterntube; 1-1/4" shaft; effective wall thickness of the cutless bearing (brass and rubber) is 1/8"; so maybe the rubber portion of that is 1/16"

-or-

2. 1-1/2" ID sterntube; 1" shaft; effective wall thickness of the cutless bearing (brass and rubber) is 1/4"; so maybe the rubber portion of that is 1/8" or more

I'm wondering if option 1 will "wear out" more quickly than option 2. I'm inclined to think it would, because the channels for water to get into the bearing are so small, so water lubrication is less effective. And the rubber is so thin, that you don't have to lose much before you're through to brass.

Has anyone found this to be true? Or would the service lives of the bearings above be practically the same?

Thanks!
Jeremy
IMHO if the water is getting in there, all should be fine. If there were a thickness problem the manufacturers probably would not make them.
Wear is due to vibration and RPM. Being submerged in a forward/aft motion keeps them cool.

If it gets loose enough to hit brass, it should have been changed out long before. The bearing should be tight enough that it can't rattle.

Age is another factor. I had an old one once that the rubber started rolling up between the shaft and the rest of the rubber.

Never run one dry! When my boat's on the hard (90% of the time for now) I spray silicone in the bearing and cover it from the sun.
__________________
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful! ........
A nation of sheep breeds a government of wolves!

Unprepared boaters, end up as floatsum!.......
delmarrey is offline   Reply With Quote
Old 15-01-2012, 13:13   #4
Registered User

Join Date: Oct 2009
Location: CLOD in OH
Posts: 257
Re: Does cutless bearing life vary depending on initial rubber thickness?

13 years and 37,000 nm cutlass bearing still tight. It is an alignment and balanced prop issue primarly and of a very minor secondary concern is the abrasives in the water you are running in. When doing an alignment it is more important to hold the shaft so it lines up with the cutlass bearing. The shaft log packing will run in and adjust to any small misalignment.
__________________
Paydirt
Mark Zarley is offline   Reply With Quote
Old 15-01-2012, 13:21   #5
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Does cutless bearing life vary depending on initial rubber thickness?

A cutlass bearing is considered worn when there is too much space between the rubber bearing surface and the shaft. This has nothing to do with how thick the original rubber bearing is.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 15-01-2012, 14:49   #6
Senior Cruiser
 
maxingout's Avatar

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Fort Pierce, Phoenix
Boat: Privilege 39 Catamaran, Exit Only
Posts: 2,606
Re: Does cutless bearing life vary depending on initial rubber thickness?

I have had Exit Only since 1993, and I sailed her around the world. We are a catamaran with two engines. I have only changed the cutlass bearings twice. Once in New Zealand, and once in Turkey. We have had good luck with our cutlass bearings.
__________________
Dave -Sailing Vessel Exit Only

http://SailingUNI.com
http://maxingout.com
http://PositiveThinkingSailor.com
maxingout is offline   Reply With Quote
Old 15-01-2012, 14:59   #7
Registered User

Join Date: Oct 2006
Location: Nanaimo, BC
Boat: C&C 41
Posts: 346
Re: Does cutless bearing life vary depending on initial rubber thickness?

A major factor in the life of a cutlass bearing, along with alignment, is the water you are in. Here, if you keep it in the Fraser river with its massive silt load, they wear out fast. In clear water they can last a very long time.
__________________
Rex Delay is offline   Reply With Quote
Old 15-01-2012, 15:11   #8
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
Re: Does cutless bearing life vary depending on initial rubber thickness?

Quote:
Originally Posted by Rex Delay View Post
A major factor in the life of a cutlass bearing, along with alignment, is the water you are in. Here, if you keep it in the Fraser river with its massive silt load, they wear out fast. In clear water they can last a very long time.
That's no joke! you can see the difference passing by.

.
Attached Thumbnails
Click image for larger version

Name:	DSCN1896.JPG
Views:	109
Size:	74.6 KB
ID:	36026  
__________________
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful! ........
A nation of sheep breeds a government of wolves!

Unprepared boaters, end up as floatsum!.......
delmarrey is offline   Reply With Quote
Old 15-01-2012, 15:42   #9
Registered User

Join Date: Nov 2011
Location: Montegut LA.
Boat: Now we need to get her to Louisiana !! she's ours
Posts: 3,421
Re: Does cutless bearing life vary depending on initial rubber thickness?

You guy's got that right! the Fraser, Columbia, Klamath, running in there runoff is enought to wear out anyones cutlass bearings LOL found that out the hard way in the Columbia cruising from the mouth to Portland, 3 weeks on a new one, still on center to! worn out when we got back to Coos Bay. Bob and Connie course it was spring
__________________
bobconnie is offline   Reply With Quote
Old 15-01-2012, 17:09   #10
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: Does cutless bearing life vary depending on initial rubber thickness?

Go for proper alignment first. Make sure the prop is well balanced. The thickness of the rubber will positively influence life only provided the two compared rubbers are of the same type, otherwise it is a wild guess as the finer rubber may be e.g. more resistant to wear (or not!).

b.
__________________
barnakiel is offline   Reply With Quote
Old 15-01-2012, 17:59   #11
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Does cutless bearing life vary depending on initial rubber thickness?

The thickness of the rubber has nothing to do with cutlass bearing life. Nothing at all. The cutlass bearing is bad when there is too much gap between the rubber bearing surface and the shaft. This has nothing at all to do with the initial thickness. Nothing at all. A 1/8" gap with the prop shaft is the same on a 1/4" bearing thickness as it is on 3" bearing thickness.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 15-01-2012, 18:19   #12
Marine Service Provider
 
jaffadog's Avatar

Join Date: Dec 2011
Location: Deltaville, VA, USA
Boat: Sam L. Morse Bristol Channel Cutter 28 ft
Posts: 13
Re: Does cutless bearing life vary depending on initial rubber thickness?

I agree with the notion that the bearing needs to be replaced when there is too much play - regardless of how much rubber is left. Nigel Calder suggests that anything more than minimal movement, defined as 1/16 per 1" of shaft diameter, warrants replacement of the bearing. Thing is, with option 1, there potentially is only 1/16 of rubber, after which I'd be getting metal on metal. Am I buying myself a headache if I go this route?
__________________
jaffadog is offline   Reply With Quote
Old 15-01-2012, 18:30   #13
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
Re: Does cutless bearing life vary depending on initial rubber thickness?

Quote:
Originally Posted by jaffadog View Post
I agree with the notion that the bearing needs to be replaced when there is too much play - regardless of how much rubber is left. Nigel Calder suggests that anything more than minimal movement, defined as 1/16 per 1" of shaft diameter, warrants replacement of the bearing. Thing is, with option 1, there potentially is only 1/16 of rubber, after which I'd be getting metal on metal. Am I buying myself a headache if I go this route?
I assume you mean 1/16 inch. That would be WAY too much for any recreational vessel.
.005" -.008" would be max for me. From the factory it's usually no more them .002", and sometimes with a little squeeze (zero tolerance) depends on the shaft tolerances. Once it starts spinning it's like a crankshaft bearing but lubed with water.
__________________
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful! ........
A nation of sheep breeds a government of wolves!

Unprepared boaters, end up as floatsum!.......
delmarrey is offline   Reply With Quote
Old 26-01-2012, 07:12   #14
Marine Service Provider

Join Date: Feb 2007
Posts: 81
Images: 1
Re: Does cutless bearing life vary depending on initial rubber thickness?

If your looking for longer service life then you may want to look alternatives to rubber as a bearing material, some composites have shown wear rates at around a third of that of rubber.
The clearances for when they need replacement are documented as are running clearances new as these are Lloyds approved for larger vessels.

Wear in a water lubricated bearing as others have said is mainly caused by alignment/vibration and also abrasive particles in the water. It is also effected by how often the shaft is run up or run down as most wear occurs at start up. Composites such as Maritex and Orkot have dry lubricants that prevent wear at these times.

The other major factor in warmer waters is marine growth on the shaft and on the bearing surface.
__________________

__________________
4HMainer is offline   Reply With Quote
Reply

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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 19:03.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.