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  #1  
Old 11-14-2013
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Confused about prop pitch, variance between prop brands

I'm looking at buying the third prop for my boat. The boat is a Pearson 28-2, 24.5' waterline, 7000lbs dry, Yanmar 2GM20F engine with 1:2.62 gear ratio transmission.

I started with the stock 16x10 2-blade "Michican Sailor" prop that served the vessel fine for the last 27 years.

Before heading out for a lot of cruising last year I upgraded to a 14x8 3-blade "Campbell Sailer". This is the prop that I've used this most. At 2800rpm on flat water the boat goes about 6 to 6.2 knots with this prop. I've measured the engine RPM using a digital/optical tach on the engine flywheel, the engine's tach is not at all accurate.

I'm now looking for a folding or feathering prop for club racing and more recreational sailing. At the top of my list is the Flex-O-Fold. They are recommending a 15x12 prop for 2-blade for 15x11 prop for 3-blade. Since my engine, waterline length, and displacement are all very common I'm assuming that they are making a good recommendation. However compared to the other props that I've used this sounds like it would be overpropped.

8" pitch to 12" pitch is a pretty big variance! Why does it vary so much?

Maine Sail has also used both a Flex-O-Fold and Campbell Sailer as noted by his (not successful) experiment in this thread:
Folding Prop Report - SailboatOwners.com

From a little digging his Flex-O-Fold was 16x12 2-blade and his CS was 16x9 3-blade. It sounds like the Flex-O-Fold was underpropped compared to the CS:
"*Slower than 3 blade under power at same RPM"

I'm also considering a Max-Prop. Flex-O-Fold is a little higher on my list due to price (about 30% cheaper), not catching kelp when sailing, and simplicity.

thanks,
alex
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Re: Confused about prop pitch, variance between prop brands

Mosaic is a 1989 Dana 24 with a Yanmar 2GM20F, a 1:2.62 transmission. Prior to 2006, the original prop was a 15x8” bronze fixed 3-blade prop. After 2006, a 3-Blade Classic Max Prop 15" dia x 10.3" pitch (10.3" pitch = 20 degrees blade angle) was installed and Wide Open Throttle (WOT) = 2800 rpm and 6.1 kts hull speed. At haulout in 2011, we decreased prop pitch by 2-degrees to 18 degrees or 15x9.2" pitch and achieved WOT = 3200 rpm. Now, she cruises nicely at 5.5 kts at 2500 to 2600 rpm. Rule of Thumb: For every 2-degree decrease in blade angle, the engine rpm will increase by 13-15%. If moored year round and because of stray electric currents, be sure to dive and change the end cap zinc every six months. At the same time, suggest cleaning the blades and exercising them. Also added a MARTYR low clearance collar zinc CMC03 (West Marine Part #4850078), which lasted 18 months. There wasn't enough clearance to use the streamlined collar zinc to ensure water flow into the Cutlass bearing. John Van Lund, Mosaic #130, Friday Harbor, WA
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Old 11-14-2013
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Re: Confused about prop pitch, variance between prop brands

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Originally Posted by Alex W View Post

I'm also considering a Max-Prop.
As food for thought, know that a Max Prop's pitch can be easily changed while the boat sits comfortably in it's slip.

Last edited by Fstbttms; 11-14-2013 at 10:34 PM.
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Re: Confused about prop pitch, variance between prop brands

Alex.. I've mentioned this before elsewhere, but FWIW, on a previous boat we went from a Martec 18x16 folder to a Campbell Sailor 17x11 with improved performance overall. The design of the CS props seem to provide a kick of thrust that requires less pitch (?)

Anyhow the point being that CS props seem to be pitched less than the others as a matter of course.

btw.. we LOVE our Max... the few hundred dollars will be forgotten not far down the road...
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Re: Confused about prop pitch, variance between prop brands

We just replaced our fixed with the Auto-stream and couldn't be happier. After 15 years of using a Maxi prop, while it worked fine and was serviceable I would never recommend them. They cause the worst prop walk of any prop I have ever used.

I tend to stick with the manufacturers recommendations on these things unless you have a lot of experience dealing with them. It is in their best interest to make sure you get the best product available.
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Re: Confused about prop pitch, variance between prop brands

I started down the path of a Max-Prop, but a couple of things made me nervous:
* 2-blade is reported to have a lot of prop-walk
* 3-blade is very expensive ($2500)

I'm judging a lot of this on the Yachting Monthly test shown here:
http://www.flexofold.com/upload_dir/...onthly_low.pdf

The 3-blade Autostream is even more at $2800, note that is more than 10% of the value of my boat. I can afford it, but honestly I'd rather spend money on sails (a new 100% jib is also on my shopping list).

For comparison the 2-blade Flex-O-Fold is $1100 and is reported to have less prop walk. The 3-blade is $1900. It also looks cheaper and easier to maintain over time since the design is so much less complex. Lower reverse thrust is a little concerning, but doesn't seem to be major.

Prop-walk is a concern for me, but also seems to be hardest to predict. I seem to get more prop-walk with my CS then I did with the stock prop, even though most people report less. My boat has very limited rudder angles (something else that I'd like to try and fix...presumably Pearson had a reason for limiting it so greatly) and the prop-walk often works against me when docking.
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Re: Confused about prop pitch, variance between prop brands

I wanted to add that I have about a mile of room between the keel and prop, and half a mile between the prop and rudder. So I don't think a 3-blade is realistically any smoother than 2-blade:


I didn't notice a difference in engine smoothness when going from the stock 2-blade (shown there) to the Campbell Sailer 3-blade.
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Re: Confused about prop pitch, variance between prop brands

Quote:
Originally Posted by Alex W View Post
I wanted to add that I have about a mile of room between the keel and prop, and half a mile between the prop and rudder. So I don't think a 3-blade is realistically any smoother than 2-blade:


I didn't notice a difference in engine smoothness when going from the stock 2-blade (shown there) to the Campbell Sailer 3-blade.
Surprised to hear that... both times we've gone from 2 to 3 blades we felt the difference was very noticeable. The first was from a rather worn 2 blade folder, to the 3 blade CS... no surprise there.

Lastly from a 2 blade michigan to a 3 blade Max.. noticeably smoother overall. and less prop walk, esp if you 'ease' into reverse rather than gun it. The reverse thrust of the Max is impressive over any other prop that doesn't 'reverse' the blades.
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Re: Confused about prop pitch, variance between prop brands

What was the under-water configuration on each of those boats?

I can see why a 3-blade prop would be a lot smoother on a full keel boat, or a fin keel boat with the prop way forward like a Yankee 30 or Tartan 30:


(Note that the prop is way forward, right behind the keel).

I can also see how prop-walk varies so much boat to boat. The leverage of the prop's side wash is a lot higher on a configuration like my Pearson than on the Yankee.

I only pick on these two boats because they are the only inboard boats that I have experience docking with. It's a lot easier to turn my boat in place using prop-walk than it is to turn the Yankee in place using prop-walk. The Yankee has a Max-Prop (3 blade), so I do have some experience with those.
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Re: Confused about prop pitch, variance between prop brands

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Originally Posted by Alex W View Post
What was the under-water configuration on each of those boats?
Both early 80s typical IOR fin/spade.. first a 40, currently 35, Kaufman and Holland designs. Very similar in behaviour all around.
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