[C320-list] Prop Shaft

[Rick Sulewski]

Tim, 
You could have your yard mechanic show you why your cutlass bearing needs to be replaced against another boat that does not, just so you can understand what is involved in the repair. While moving to a SS shaft has several advantages such as less flex and hence less vibration in addition to less wear and tear on the stuffing box packing, a worn cutlass may be the result of many factors, including engine misalignment, worn engine rubber mounts, a prop that is out of balance and even a prop strut that may have suffered some stress if it  hit an object, etc. If your cutlass bearing is replaced and you move to a SS shaft, your mechanic will be checking/adjusting the engine and shaft alignment after the repair is completed and the boat was allowed to rest (unflex) for a while in the slip. No doubt he will also check the condition of your motor mounts.

Based on my experience with my 95' 320, my cutlass bearing was replaced when I moved to a SS shaft in year 3 at 400 hours after wrapping a line while underway.  It was replaced again in year 18 at 1200 hours  with the latest and greatest harder cutlass bearing material. I  regretted not replacing the shaft log hose at that time when I replaced the cutlass bearing using the association tools. I had the prop rebalanced each time the cutlass bearing was replaced. At 1300 hours I replaced the shaft log hose and had to buy a coupler puller, but fortunately I could reuse my coupler on my freshwater  boat.

 If your boat is approaching 20 years and 800 hours,  based on my experiences you may well need a cutlass bearing replacement, especially if the engine alignment or motor mounts have not received attention during that same time span. Consider having the prop balance checked if your prop has fixed blades before the prop is reinstalled during the cutlass/shaft replacement. You may want to consider the condition of the shaft log hose which is rubber if your boat has a standard flax ring stuffing box. If you are removing the cutlass bearing and shaft,  that is the best time on a 20 year old hull to replace the OEM shaft log hose with a more robust one.  
Rick Sulewski 
My-Ria 95' 320 hull 277

FYI - One of the many things I learned from my daughter who is a polymer engineer while she was completing her dissertation on the various elasticity and strengths of different rubber and synthetic compound mixtures is that carbon based  materials will deteriorate over time or begin to wear excessively as the component ages under various conditions. If you look closely at the different cutlass bearings in your boat yard while  boats are on the hard it is apparent that cutlass bearings do wear and age differently. There are often  visible signs in addition to the shake test. Newer harder bearing materials  will wear better,  but will still wear out.  Older bearings seemed to be softer and may even  appear to be visibly cracking/fracturing due to age. Newer synthetic cutlass bearing materials may still compress while the boat is on the hard due to the hull flex  induced misalignment of the shaft that is visible when sighting the shaft in the cutlass bearing with one end of the bearing material edge pushed down in the strut and the opposite end pushed up because of  hull flex aft of the engine grid. Consider that the hull is being unnaturally supported especially in a cradle more so than on jack stands. That unnatural hull flex position may actually exaggerate the ability to move (shake) the shaft up and down while movement side to side may be a better indicator of a worn cutlass bearing while on the hard.   That induced flex due to storage  is not the same cutlass bearing condition if the hull was in the water for about a week or more and allowed to relax back to its normal (un-flexed)  disposition.

-----Original Message-----
From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Tim
Sent: Tuesday, April 24, 2018 12:20 PM
To: c320-list at lists.catalina320.com; c320-list-request at lists.catalina320.com; c320-list at catalina320.com
Subject: [C320-list] Prop Shaft

Hi All - 
I had some play in my cutlass bearing after about 4 yrs of light motoring (<100hrs per year) and the yard mechanic is suggesting to replace the prop shaft. He is stating that  bronze is too soft and wears too quickly. My boat is a 99 with less that 800 hours in total.
Does this sound reasonable or do I need to find another mechanic?
Thanks
TimCalypso#603