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Old 07-01-2017, 05:45   #1
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Flexofold size vs fixed prop

We're considering switching from the 3 bladed fixed prop on our Beneteau 37 to a Flexofold 3 blade. I've reached out to our dealer and to Flexofold to find out what size they would recommend. The original fixed prop is 17" diameter x 12" pitch, 3 blades. Our dealer said they would outfit it with a 16x12 3 blade FOF. Flexofold themselves has recommended a 15x10. I'm curious why the Flexofold sizes, both from the dealer and especially from FOF are so much smaller than the OEM fixed size. Has anyone made this conversion and had similar size changes? If so, how has that worked out in terms of cruising speed under power?

Boat displacement is 14,400 lbs. Engine is Yanmar 3YM30. Currently we cruise at about 7.2 kts at 2775 RPMs. We know the sailing performance will be better with the FOF but want to motor a little faster too. Just wondering if there's something about the FOF geometry that gives it more bit inspite of the smaller size.
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Old 07-01-2017, 06:22   #2
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Re: Flexofold size vs fixed prop

Greater the clearance between the hull and the prop the quieter and smoother it will run.

I would go with the manufacturer recommendation over any other since they are the ones you will have to deal with if you have a problem and they are the ones who know their product better than anyone else.

Just make sure the manufacturer has all of the correct info regarding boat type, displacement, waterline length, engine type, gearbox, and rpms.
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Old 07-01-2017, 08:09   #3
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Re: Flexofold size vs fixed prop

I replaced the original 3-blade prop on my Beneteau 473 with a Flexofold 3-blade. I don't remember the exact sizes but it seems to me the Flexofold was a bit smaller in diameter. I provided Flexofold with the engine and transmission specs and then went with their recommendation.
I'm very happy with the Flexofold. Faster under sail and while motoring. Less prop walk in reverse too. When you're under sail and after shutting down the engine, remember to shift into reverse for a moment to cause the prop to fold, then back to neutral.
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Old 07-01-2017, 08:39   #4
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Re: Flexofold size vs fixed prop

I changed the fixed prop on my Oceanis 40 to a flex o fold last April. One of the nicest changes I have made to the boat. I went with the manufactures recommendation based on the engine and transmission information that I sent them. It was smaller and a different pitch than OEM. Boat sails faster and motors faster.
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Old 07-01-2017, 08:47   #5
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Re: Flexofold size vs fixed prop

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I changed the fixed prop on my Oceanis 40 to a flex o fold last April. One of the nicest changes I have made to the boat. I went with the manufactures recommendation based on the engine and transmission information that I sent them. It was smaller and a different pitch than OEM. Boat sails faster and motors faster.


Captainjay,

Thanks for the info. Do you remember if the FOF was smaller both in diameter and pitch, or smaller in diameter but larger pitch?
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Old 07-01-2017, 09:47   #6
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Re: Flexofold size vs fixed prop

My experience has been that folding props are usually larger do to the surface area design used to fold properly. Also they have poor performance in reverse .
I replaced a 2 blade fixed prop that was too small for the 30 foot boat, with a MAX feathering 2 blade prop and it was night and day. Also feathering props always keep the cutting edge of the blades towards the direction the thrust is applied because the edge turns 180 degrees when in reverse and therefore reducing prop walk. That may or may not be what you want, I find prop walk useful when docking. If the manufacture does help you solve your question there a few prop repair and engineering firms that might be be ble to help.
My two cents. All the best.
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Old 07-01-2017, 11:39   #7
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Re: Flexofold size vs fixed prop

I bought a two blade Flex-o-fold at the Düsseldorf boat show from the factory rep. All he asked was engine hp and transmission.

When the prop arrived, I had the immediate problem of the folding prop hitting the skeg when folding. Open the prop had clearance, closed it had clearance but in between it hit the skeg.

My choice was to cut a notch in the skeg, which on a Pearson 36 wouldn't weaken anything or go with a smaller prop.

I went with a smaller diameter and I think I lost maybe 1/2 a knot at cruising rpms (2500).

On the upside, there is much less prop walk and the company give great service, at least when dealing with the home office in Denmark.
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Old 07-01-2017, 15:58   #8
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Re: Flexofold size vs fixed prop

Put on my 51 beneteau a 20" Gori it's been great over the fixed 20".the boat can be driven in reverse almost as easily as in forward.
Ernie on the Mary Jane
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Old 07-01-2017, 16:58   #9
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Re: Flexofold size vs fixed prop

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Captainjay,

Thanks for the info. Do you remember if the FOF was smaller both in diameter and pitch, or smaller in diameter but larger pitch?

The original prop was 18 x 14 the flexofold is 17 x13
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Old 07-01-2017, 17:20   #10
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Re: Flexofold size vs fixed prop

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The original prop was 18 x 14 the flexofold is 17 x13


Perfect. Thanks for the info. I have an email in to FOF for clarification, but I'm glad to hear it's not unprecedented to go down in both dimensions and still motor faster.
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Old 07-01-2017, 18:22   #11
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Re: Flexofold size vs fixed prop

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Originally Posted by Davidasailor View Post
We're considering switching from the 3 bladed fixed prop on our Beneteau 37 to a Flexofold 3 blade. I've reached out to our dealer and to Flexofold to find out what size they would recommend. The original fixed prop is 17" diameter x 12" pitch, 3 blades. Our dealer said they would outfit it with a 16x12 3 blade FOF. Flexofold themselves has recommended a 15x10. I'm curious why the Flexofold sizes, both from the dealer and especially from FOF are so much smaller than the OEM fixed size. Has anyone made this conversion and had similar size changes? If so, how has that worked out in terms of cruising speed under power?

Boat displacement is 14,400 lbs. Engine is Yanmar 3YM30. Currently we cruise at about 7.2 kts at 2775 RPMs. We know the sailing performance will be better with the FOF but want to motor a little faster too. Just wondering if there's something about the FOF geometry that gives it more bit inspite of the smaller size.
To add to the praise for Flexofold, we have one (three blade) on our Oceanis 50. Folds perfectly under sail, and under power, you would not know you have a folding prop. The thought of dragging a fixed three blade through the water while sailing convinced us to go the extra from the start, so I cannot give you any before and after as there was never a 'before', but I think the other comments here are convincing enough in that regard
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Old 09-01-2017, 04:42   #12
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Re: Flexofold size vs fixed prop

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Originally Posted by Davidasailor View Post
Perfect. Thanks for the info. I have an email in to FOF for clarification, but I'm glad to hear it's not unprecedented to go down in both dimensions and still motor faster.
It is a much more efficient prop shape.
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Old 09-01-2017, 10:44   #13
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Re: Flexofold size vs fixed prop

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Originally Posted by Davidasailor View Post
Perfect. Thanks for the info. I have an email in to FOF for clarification, but I'm glad to hear it's not unprecedented to go down in both dimensions and still motor faster.
It also isn't uncommon for older boats to end up with the wrong prop. Old calculators weren't as good as modern ones, some builders would just grab something off the shelf, and frankly a lot of PO's do weird things from time to time like install oversized props. FOF has a good service reputation, and if they make the recommendation I would assume they will swap it out if they are wrong.
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Old 11-01-2017, 07:32   #14
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Re: Flexofold size vs fixed prop

Quote:
Originally Posted by Davidasailor View Post

Boat displacement is 14,400 lbs. Engine is Yanmar 3YM30. Currently we cruise at about 7.2 kts at 2775 RPMs. We know the sailing performance will be better with the FOF but want to motor a little faster too. Just wondering if there's something about the FOF geometry that gives it more bit inspite of the smaller size.

Hi David

It sounds like your current prop size is just about ideal. I believe the 3YM30 has a max RPM rating of around 3600 RPM, so your cruising RPM should fall within 75%-80% of that value, which equates to around 2600 RPM. The theoretical hull speed for your boat is 7.8 kts and if you are currently getting 7.2kts @ 2775 RPM, you are just about spot on, so I wouldn't expect any miracles from a "properly sized" FOF when it comes to motoring.

The key being "properly sized". If you get your new FOF and suddenly find that you can motor at 7.6 kts down at 2200 RPM, then you may likely be oversized. Keep a look out for signs of black smoke coming out of the exhaust on your sea trials. A good sign of engine overloading.

The nice thing is that based on the numbers, it seems your current prop is an excellent reference point. The FOF dimension should be close to your current prop and if it is one size smaller, then it sounds like the right direction, as it shouldn't overload the engine. If it was much bigger, I would be skeptical.

If you can, please let us know your results. I am considering a FOF for my 3YM30 powered Jeanneau 36i.

Cheers.
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Old 11-01-2017, 08:39   #15
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Re: Flexofold size vs fixed prop

Hi David

I just heard back from AB Marine. I had inquired about sizing for a 3 blade Gori on my Jeanneau 36i which has the same engine and similar displacement to your Bene 37. They came back with a 16.5 X 12 three blade. This is very close to what your dealer was recommending in the FOF.

This makes me think that perhaps FOF is erring on the side of under prop in their 15" diameter size recommendation.
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