Prop Shaft Replacement

[Ron Hill]

Steve : I've done some thinking and believe that I figured out the shaft length problem.  
The older C34's have a M25/M25XP engine which has 3 cylinders.  The later boats have an M35 engine with 4 cylinders and is one cylinder longer than the M25 engine.  So the M25 engine needs a longer 58/59" shaft as opposed to the 55" shaft for the M35 engine.

I just talked to Gerry Douglas and appraised him of the problem.  He said that Catalina makes their own shafts so it shouldn't make any difference.  I told him the info that his parts dept was putting out and asked if he would look into the shaft length problem.  He said he would.  
I also mentioned that beside the 1000+ C34 that need the longer shaft that 1000+ C36's were probably in the same predicament.

[Stephen Butler]

Ron: Appreciate the technical followup!  I have gone back to Kent at Catalina for specs for the prop shaft on our boat and the OD of the cutlass bearing.  If I can get these from Catalina, I can have a new shaft and bearing waiting for us at the boat when we arrive on the 20th of December.  About the reason for the different prop shaft lengths...you are exactly correct...checked the difference between the block lengths of our M25XP and the M30 series and the missing inches are there!  Another interesting comment from our potential supplier in Ft. Lauderdale (F & J Prop Shop); they still quote a lot of bronze, and stock it, but have not sold one for almost 20 years....not much cost difference from the ss and the ss has much better corrosion resistence.

So, now waiting to hear from Kent for the prop and bearing specs.  Would certainly have preferred to purchase from Catalina, but think we are now out of time.  Oh well, another time.  Thanks again.

[Mike Vaccaro]

"Common wisdom" dictates that stainless steel is a better shaft material than silicone bronze.  From a stress and capabilities point, it is, but that is largely irrelevant for the small, low-load application such as the prop shaft in the Catalina 34.  From a corrosion-resistant standpoint, silicone bronze is the better material.  While it will wear faster than stainless, it is a more robust material under the water.  While there is sufficient oxygen in water to form a protective layer of oxidation on 300-series stainless, there is also sufficient chloride to attack it.  Also, the more dissimilar metals mixed under the water, the better the battery--especially true in salt water.  In a "perfect" installation, the shaft, prop, bearings and strut are all made from the same material and electrically isolated from the gear box.  From a corrosion standpoint, bronze is a better choice, if it structurally adequate.

Realistically, it doesn't make much difference, but in all cases it's critical that the zincs be properly installed and maintained below the waterline.  The degradation of the zinc will be accelerated if dissimilar metals are present (e.g., a stainless shaft attached to a bronze prop), or there is a problem with electrolysis (usually caused by a fault with AC dock power if the boat is not equipped with a galvanic isolator [good] or isolation transformer [best]).  If a stainless shaft is used, it needs regular inspection to check for corrosion.

Cheers,

Mike