Stainless Steel vs. Bronze Prop Shaft

Jul 12, 2011
1,165
Leopard 40 Jupiter, Florida
I am going to replace the three-blade fixed propeller on my Catalina 36 (1999) with a feathering three-blade Max-Prop this winter. The yard doing the work and the Max-Prop distributor, PYI, have been really helpful in sizing and advice. One suggestion confused me, and I want your feedback before dropping an additional $500. They both suggested I replace the original bronze propeller shaft with a stainless one ($400). Naturally, if I pull the shaft, I might as well do the cutlass bearing at the same time. Both of them gave me vague answers about stainless being stiffer than bronze, reducing vibrations as it will not flex as much, and is more wear and corrosion resistant (we're fresh water, but theoretically things rust here too). I cannot detect vibrations now, but perhaps with a feathering prop these will increase (?). I do not disagree with their comments (stiffer, resistant, etc.), it's just that I don't seem to have problems now, and do not seem to need any improvement.

Any advice is worthwhile. Will the forces on a feathering prop be different and stronger than the fixed-blade?
 
Oct 1, 2007
1,857
Boston Whaler Super Sport Pt. Judith
Couple of points:
1. Modulus of elasticity of SS is approximately double that of bronze typical in propeller shafting for recreational boats. So yes, SS is "stiffer" and a SS shaft for your boat will be "stiffer" per size.
2. Vibration depends on much more than the modulus of the shaft. No guarantee replacing bronze for SS will have any effect on vibration.
3. Bronze shafting may actually more resistant to the environment than SS. However, since you are in fresh water this is not an issue.
4. I have a 1-1/4 in SS shaft with an 18 inch MaxProp. Smooth as silk.

I have dealt with PYI for years with very good success.
Good luck
 
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Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
They should be quoting you on an AQ-22 or AQ-19 shaft (Aquamet or Aqualoy shafting). This shafting not typical SS and it far exceeds bronze shafting in all areas. The old bronze shafting (Tobin Bronze) was really closer to a brass anyway.

Western Branch Metals is the leader in prop shafting so be sure they are not quoting you a lesser product.
 
Jul 12, 2011
1,165
Leopard 40 Jupiter, Florida
Thanks Maine. I casually used "stainless" as shorthand. I've read your excellent posts on the Aquamet / Aqualoy products, and your illustrated article on propeller fitting and lapping (thanks!). Unfortunately, I do not feel mechanically experienced (nor have sufficient time) for this to be a do-it-yourself job, so must depend on the boatyard. The hard part will be "suggesting" that they do it right by asking the important questions about how they plan to do this job. First time doing major work through a boatyard, so I don't know how sensitive they will be.
 
Feb 14, 2014
7,400
Hunter 430 Waveland, MS
For short shafts (properly aligned), 3 bladed props, <3000 rpm, good engine mounts and a good strut/cutlass bearing you should have no vibration issues.;)
Matching shaft to propeller metals helps minimize you galvanic corrosion.
But with good shaft zinc maintenance in fresh water:snooze:.

Since I am in salt water, if I ever change, I would look for Alloy 20 SS (mainly for elimination of stress corrosion cracking)
Rick486 is on the engineering target!

Jim...

PS: 3 bladed (power prop) vs 2 blades has few vibrational issues either.
 

Gunni

.
Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
The hard part will be "suggesting" that they do it right by asking the important questions about how they plan to do this job. First time doing major work through a boatyard, so I don't know how sensitive they will be.
Parsons, the suggested install and related upgrades do sound like the proper approach. Get the shaft, cutlass and aligned coupling all right now. It is your boat, and your money, and their trade professionalism at stake here. As long as everyone keeps those ground-rules in mind it will be smooth. You are not an expert, but you are an informed, concerned owner. Ask a few questions, define what is important to you (done right, money second, final results, examples of previous similar work, etc.) and determine whether they understand your expectation. Done diplomatically a competent tradesman will appreciate the definition. There should be zero emotion in this. I would not do the work with out a written scope with part specifications and an estimate of costs. Taking shortcuts on that process is how you end up with misunderstanding and little recourse. Good luck captain, you are going to love that Max-Prop!
 
Jul 12, 2011
1,165
Leopard 40 Jupiter, Florida
Wow -- I've got all the heavy hitters giving me advice! Many thanks guys for your experience and willingness to help. I think that Gunni's summary is great. I feel much more confident now dropping the additional money for a quality job.
 
Jul 12, 2011
1,165
Leopard 40 Jupiter, Florida
To wrap this thread up, I had our local yard install the 3-blade MaxProp with a new Aquamet shaft and cutlass bearing replacement right before the boat splashed this spring. They had to remove and replace the rudder as they could not get the shaft past it, although some C36 owners reported that it was possible after pulling the cutlass to allow lateral movement. The cost to have it professionally done was about $5,000, but I'm confident of the work quality. The boat yard was very understanding that I wanted to watch this done, so I stayed for the entire adventure.
20170503_165436_resized.jpg
The final product is a great improvement over the old 3-blade fixed Michigan Wheel. The boat has less prop walk in reverse, and stops on a dime. In fact, I had to adjust my docking as I used to put it in slow reverse approaching my slip and slow down as I coasted forward. With the new prop, I'd stop halfway into the slip as the boat would no longer coast. I've not seen appreciable slower motoring and reach hull speed around 2,100 rpm. The low wind sailing has improved, but there is no change for higher winds as I reach hull speed before the drag of the prop affects things. In summary, I think it was a good investment for my boat.
20170503_171551_resized.jpg
 
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Gunni

.
Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
Nice job. You hit on the two best features of the MaxProp - great light wind performance and immense thrust in reverse. Shut it down in forward to feather, then move to neutral. Keep a shaft anode on it, the MaxProp anode is not enough.
 
Oct 22, 2014
20,996
CAL 35 Cruiser #21 moored EVERETT WA
Parson's thanks for the thread and insights shared by the crew here. good stuff. Hope you have a great summer running your feel like new boat.... :biggrin: