Flexofold prop performance - SailNet Community
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post #1 of 10 Old 4 Weeks Ago Thread Starter
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Flexofold prop performance

I just got the boat back in the water after being on the hard for gelcoat repairs, bottom paint, and a good polish and wax. While she was out I also installed my new Flexofold prop in place of the stock ZF fixed prop.

With the fixed prop our cruising speed at 2500rpm was 7.5kts. Full throttle gave us 8.7kts.

On my way back to the club today I checked boatspeed and found that I could hit 7.5kts at about 2200rpm, and 2500rpm had me going 8.4kts! I pushed it up to full throttle and we got up to 9.7kts! I read that the FOF was an efficient prop, but I didnt expect to gain a full knot on our cruising speed!

Backing out of the slip at the boatyard I found that propwalk was minimal. Certainly far less that the fixed prop produced.

Of course when I pulled in to my slip, the stopping power was definitely less that the fixed prop, which would stop on a dime, but that is a trade off I can live with. You just have to use higher rpms and hit reverse a bit sooner.

I can't wait to get out for a sail and see what kind of speed improvements I get!



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Re: Flexofold prop performance

What's going on with the strut???
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Re: Flexofold prop performance

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What's going on with the strut???
Nothing going on with the strut, I just hadn't cleaned off the old paint and barnacle feet yet.

It looks a bit crooked in the pic but that is just an optical illusion.

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Re: Flexofold prop performance

Your experience is similar to my first season with my new 3-blade 15x9 FOF prop. The FOF has a higher EAR than most "sailer" type props (the ones with narrower blades for less drag), making it more efficient when motoring. And, of course, it's much less drag when sailing, so you're getting the best of both worlds. [EDIT: After looking at your "before" picture, it appears that you didn't have a "sailer" type prop, but a more typical powerboat-like prop.]

I too noted less prop walk and a little less thrust in reverse. But I'm easily able to apply more throttle in reverse when I need it.

You should note that getting higher speed at a given RPM is not necessarily a good thing. Props don't create more power, they just transmit your motor's power to the water. The price you pay for getting higher speed at a given RPM is greater load on the motor, which if excessive could lug the motor, leading to carbon deposits and difficulty making way if you're motoring against strong winds. The key test is to make sure your motor gets to the manufacturer's rated maximum RPM at full throttle (with clean bottom and smooth water). If not, your motor isn't able to produce full power and will strain when you need to have that power.

I had been warned that many have to reduce their pitch by an inch or so when switching to a similar diameter FOF. My motor is rated at 3000 RPM maximum, and I was getting 3400 at full throttle with my old 9" pitch "sailer" prop, so I stuck with 9" pitch on the FOF and I now get 3200 RPM at full throttle. This is still a little above 3000 RPM, but Maine Sail advises that it's better for max RPMs to be a little too high than too low.

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Last edited by TakeFive; 4 Weeks Ago at 01:06 AM.
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Re: Flexofold prop performance

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Originally Posted by TakeFive View Post
Your experience is similar to my first season with my new 3-blade 15x9 FOF prop. The FOF has a higher EAR than most "sailer" type props (the ones with narrower blades for less drag), making it more efficient when motoring. And, of course, it's much less drag when sailing, so you're getting the best of both worlds. [EDIT: After looking at your "before" picture, it appears that you didn't have a "sailer" type prop, but a more typical powerboat-like prop.]

I too noted less prop walk and a little less thrust in reverse. But I'm easily able to apply more throttle in reverse when I need it.

You should note that getting higher speed at a given RPM is not necessarily a good thing. Props don't create more power, they just transmit your motor's power to the water. The price you pay for getting higher speed at a given RPM is greater load on the motor, which if excessive could lug the motor, leading to carbon deposits and difficulty making way if you're motoring against strong winds. The key test is to make sure your motor gets to the manufacturer's rated maximum RPM at full throttle (with clean bottom and smooth water). If not, your motor isn't able to produce full power and will strain when you need to have that power.

I had been warned that many have to reduce their pitch by an inch or so when switching to a similar diameter FOF. My motor is rated at 3000 RPM maximum, and I was getting 3400 at full throttle with my old 9" pitch "sailer" prop, so I stuck with 9" pitch on the FOF and I now get 3200 RPM at full throttle. This is still a little above 3000 RPM, but Maine Sail advises that it's better for max RPMs to be a little too high than too low.
Full throttle is 3200rpm with the FoF which is the same max rpm I got with the fixed prop. The big difference was 1 knot higher boatspeed. I can only assume the better boatspeed is due to a superior blade design. It certainly wasn't overloading the engine or it wouldn't have been reaching the same max rpm.

I am curious, what kind of performance increase did you notice when you switched to the FoF?

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Last edited by SchockT; 4 Weeks Ago at 03:47 AM.
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Re: Flexofold prop performance

Just to be clear, the standard is that you reach max rated rpm at wide open throttle, while underway. Not just that it matches the old prop, which could have theoretically been wrong. Sounds like you're likely in good shape though.

I'm afraid I have to call something amiss with a 39ft boat (estimate 35 LWL) making 9.7kts over the water. Hull speed would be approx 8 kts. You'd have to be incredibly over powered, not just an efficient prop. Was that speed over ground, assisted by current, perhaps?
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Re: Flexofold prop performance

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Originally Posted by Minnewaska View Post
Just to be clear, the standard is that you reach max rated rpm at wide open throttle, while underway. Not just that it matches the old prop, which could have theoretically been wrong. Sounds like you're likely in good shape though.



I'm afraid I have to call something amiss with a 39ft boat (estimate 35 LWL) making 9.7kts over the water. Hull speed would be approx 8 kts. You'd have to be incredibly over powered, not just an efficient prop. Was that speed over ground, assisted by current, perhaps?
I am going to do further testing to verify, but unless something changed in the calibration of my knot meter in the 2 weeks the boat was out of the water, it has always been accurate. Unfortunately I was fighting an ebb tide my whole trip so wasn't able to verify with the GPS. Speed over ground was over 1-2kts slower, until I got out of the current in the Cove where the boat lives. Once I got out of the current the knot meter and gps agreed with in .2kts, but at that point I had to slow down to 5kts.

The max rated engine speed for my engine is 3300rpm, and on my boat wide open throttle is just over 3200 with both props.

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Re: Flexofold prop performance

Hull speed and speed motoring forward arenít the same thing. My boat with a FOF can exceed hull speed when motoring if not going into current/waves/wind.

For what itís worth Iíve had both a MaxProp feathering prop and A FOF. The FOF is sooooo much better in things important unless all you care about is going crash reverse all the time.

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Re: Flexofold prop performance

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Hull speed and speed motoring forward arenít the same thing. My boat with a FOF can exceed hull speed when motoring if not going into current/waves/wind.



For what itís worth Iíve had both a MaxProp feathering prop and A FOF. The FOF is sooooo much better in things important unless all you care about is going crash reverse all the time.
It makes sense that the FoF would be superior to the feathering props. Feathering props have symmetrical foils for blades which does not allow for efficient operation. The ability to "twist" the blades on the folding prop allows them to make the most of the entire blade surface.

The FoF seems particularly well engineered.

"Crash stops" are not something that is important to me. There are very few scenarios I can think of where you would need such a thing. Once you get used to how quickly the boat stops with the folding prop you can easily compensate for the reduced stopping power when docking.

A friend of mine once said " never approach the dock faster than you are prepared to hit it!" Sage advice to live by!

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Re: Flexofold prop performance

here's ours...half way between Hi and the mainland in ~20k' of water

every bit as fast in fwd as the old autoprop, a little less reverse and a little less prop walk. but no maintenance and the peace of mind of it folding.

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