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Ahoy,
Patricia Bess is a 1983 424 ketch with the original Westerbeke 58 engine.
I have owned her since Oct 2014.
I have always thought she was a bit sluggish under power, but had no idea how
much until I buddy boated with a friend. When we motored side by side he was doing
5 kts at 1800 rpm (Catalina 36) and I was doing 2500 rpm to keep up.
After reading a number of forum postings on speed vs rpm as well as prop size,
it’s easy to see I have a problem.
From what i’ve read, the original prop on the 424 is a 12”x13”LH three blade.
The prop on the Patricia Bess is a 18”x11”LH three blade.
I can see from past surveys that the boat has had the smaller prop since at least Sept 2005.My questions are:
Did all 424s come delivered with 20”x13” props on 1.5 shafts?
What should I expect if I reprop to a 20”x13” prop? (rpm vs speed)
Why would the PO down size to the 18”x11” prop that’s now on the boat?
Can I repitch the prop I have to a 18”x13” to get more power?I do not want to spend $3000 plus for an adjustable prop.
Any input is greatly appreciated.
Ron Feigenbaum
S/V Patricia Bess
#218 -
Ahoy,
I recently repowered Discoverie, and when I started to research the power train I found The Propeller Book by Dave Gerr. I think used copies in paperback are available for about $15, shipping included.Gerr has written quite a collection of books and articles— you can a list of them here at his site http://gerrmarine.com. Hopefully others with W58s can give advice based on experience, but my W58was on its last legs so I don’t have good data for you. I stuck with the flexifold the PO had installed and used that as a constant when selecting an engine.
Understanding the optimum prop for your vessel will include knowing the power at the shaft. Gerr’s Book does a good job of explaining the details.
Here’s a link to one of his articles on blade area in Sail magazine. https://www.sailmagazine.com/diy/propeller-blade-area
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My 424 came with a 20×13 fixed prop, still on a shelf here in my family room.
I assume you’ve read my notes, http://www.richardcarter.net/repower/Propeller.html . This has a spreadsheet linked you can download to calculate propeller size.
The article linked above is interesting but might be a bit more than most folks can chew on. Many newer engines rev at a higher RPM than the old beasts Pearson used when the 424’s were built. As a result, you get a higher shaft speed at power settings with a new engine unless you do something to change the gear ratio. I was replacing the V-drive at the same time I repowered so I changed the gear reduction there, keeping the old 1:1 velvet drive. If you repower to something that runs 30% faster than the old engine, you’ll get a shaft speed 30% higher. I switched to a 2.5:1 gear in the V-drive to get the shaft speed back down closer to what Pearson designed. I would have gone a bit higher but that’s the most Walter had.
Rich
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