New prop question / Maybe nuking things out

[AnnOMalleys]

I recently sent my 2 bladed 63mm Max-prop in to get refurbished. PYI recommended buy a new (refurb) from them, because refurbing mine would be about $200 more than the cost of the purchased refurb... Either way , it's several hundred dollars more than I'd like to spend. Cost projection was $300-400, not a boat unit +.
This is where it gets to the nuking part. The Westerbeke manual ( I have a 44b in my boat) gives recommendations based on reduction ratio and ERPM. I have a newage PRM 120 pushing a Walter V-drive which spins the shaft. Both units have a 2:1 R/R. Shouldn't the overall R/R of the system be 4:1? Multistage reduction systems you multiply the ratios of each stage...
And I obviously need to determine cost / value ration for buying a refurb vs a new more affordable prop

[David M]

Are you asking which size you need?

[AnnOMalleys]

Actually a two part question -
1) What's the reduction ratio I use to select a prop?
2) Just about every discussion I've read has said Maxi-Props are darned good props. I'm not racing, I'm coastal, maybe some water sailing">blue water sailing in a year or two. Is it worth a 400-700 dollar difference? Go with a good 2 or three bladed fixed instead, and save a bunch of dough...

[UNCIVILIZED]

You'll likely both drive yourself mad, trying to figure out exactly what size, & pitch prop to get, based on the info which you're currently working with.
Yes, there's a science to picking a prop, or rather, getting close anyway. But much of it's based on data compiled over time. Factoring in; hull shapes, engine & transmission gearing, boat weight, underbody profiles, windage, engine torque curves, etc. etc.

If you get a Max-Prop, the pitch is adjustable with it on the boat, with the boat in the water.
Plus they give a superb amount of thrust in both forward AND reverse. Not to mention next to no drag when sailing. Oh, and they ain't half bad when it comes to fuel consumption either (sic).

Unless you're budget's super tight, snag one, or one of their competitors. There are a couple of other brands which also offer great efficiency in terms of power transmission, both in forward & reverse, that you'll run across on here if you do a bit of digging (or someone's kind enough to chime in about).

The bottom line (for me anyway) about them, is how much thrust which they can generate in only a couple of seconds, when shifting them from forward into reverse (and vice versa).
That confidence removes a lot of the sense of hairiness out of close quarters maneuvering.

[westwinds]

Your two reductions of 2:1 will result in a 4:1 reduction. Your propeller RPM is going to be lower than most boats. Is this a custom installation? If so go buy Propeller Handbook by Dave Gerr if you want to go with a cheaper fixed blade. You say this is a 63mm propeller which is probably really a 63cm so that is a diameter of about 25 inches. What happened with the old propeller? Is the material all eroded from cavitation because a high pitch was needed to get the engine RPM down to a reasonable value? I am thinking your propeller diameter is too small for such a slow turning propeller. However, a slow turning propeller is less likely to have a cavitation problem. Talk to you propeller manufacturer and tell them what your horsepower is going to the propeller and what the maximum engine RPM is with the 4:1 reduction. Also tell them how much clearance there is between the propeller tips and the bottom of the boat. Do not measure straight down from hull to propeller tip. Instead, move the ruler back and forth from tip to hull to find the least distance possible. I am thinking you will need a bigger propeller, either a larger diameter, or more blades.

[Capt Gary]

Seems like you are getting a pretty high estimate for refurbishing your 2 bladed prop. I had my 18x14 repitched to 18x16 and refurbished/rebalanced at Hale propeller in Old Saybrook, CT for about $200. They did an awesome job!

[AnnOMalleys]

Capt Gary - PYI quoted me - caveated of course because they hadn't seen the prop- an average prop refurb from them is in the $400 range. Thats what I was sort of figuring on. But, my prop has been sitting in saltwater for over two years with no cathodic protection at all, and I don't know when it was serviced before that. It could be original for all I know

[Captain Bill 3]

You guys are all missing it, contact PYI again and ask them for recommendations. Stay with the max prop, go to a 3or4blade for superior smoothness and max thrust. If you don't get it right the first time, you can always change it at haul out for no charge. Water proof grease will last a season, don't forget to use the grease fitting that comes with the prop, regular fittings don't work well.
The props work great, used to sell them, have one on my boat.