FlexoFold Prop Size Identification/Confirmation

[Mike McDonald]

I am trying to confirm the size of a FlexoFold prop that came with my boat.  I currently have a fixed 3-blade prop on the boat, but this prop was part of the package when I purchased the boat.  I'm not sure if it was ever on the boat, and if so, why it was removed.  I have copied a photo of the blade identifiers for reference and identification.  I received an email with a photo from FlexoFold showing how to identify the size, but it doesn't exactly match what I have.  I believe that it is a 10x15 prop, but want to confirm.  After reading many of the posts on this forum regarding FlexoFold props, it sounds like 10x15 would be a good size for a MK I with a M25-XP.  If any of you recognize the markings, I would appreciate your feedback. 
I am hoping that it will provide improved overall performance and minimize prop walk in reverse.  It seems that this has been the experience of those on this forum who have installed this prop.  I am also trying to find the owner info for this prop, Parts diagram / installation instructions, etc.  I hope the picture comes through.   Thanks.
Mike.....

[Clay Greene]

Yes, that looks like a 15 inch diameter by 10 inch pitch prop.  We had a 15 x 9 on our 1989 C34 with the M25XP engine based on the recommendation from Flexofold.  The 15 x 9 worked well for us - definitely improved performance under power compared to the fixed prop and much less prop walk.  We were able to get the engine up to full RPMs without temperature or exhaust issues so it seemed to be the right combination to us. 

I can't say whether the additional inch of pitch will make it over-propped - others may have first-hand experience.  The fact that PO had the Flexofold and went back to the fixed prop suggests that there was something wrong with it.  I don't know why anyone would go back to a fixed-prop if the Flexofold worked as intended.  If it is a problem, you can get replacement blades from Flexofold and they may take your current blades in trade.  Unfortunately, their customer service is in Denmark now and they are not as easy to deal with as when they had a U.S. salesperson. 

[Mick Laver]

Agreed. It's a 15x10 right-hand prop. From what I've read here it should work great with an M25. It looks like an older model, since the newer ones (installed ours Feb 13) are stamped something like 1510-3R. I'll try to attach a picture. I did find the installation instructions at http://www.flexofold.com/upload_dir/docs/3-blade-US-shaft-2_0_2013.pdf.

I also agree that it's very strange it's not installed. It's one of the best upgrades you can make IMO. Better performance forward, more control and less propwalk astern, and oh there's that sailing thing ....  We put a 2-blade Flexofold on our C30 and a 3-bladed 15x9 on our C34 (M35B). The ONLY reasons I can think it wasn't on your boat are 1) it had never been installed and the PO had bought the prop used or 2) the PO was doing some long-term cruising and wanted one less moving thing with moving parts that could break. The latter is very speculative since I've never heard of one failing.

The one knock I have on the Flexofold (and perhaps this applies to folders in general) is that it doesn't seem to stop - or engage as quickly - as my 3-blade fixed. We have a downwind slip in a fairly windy area (they do exist in San Diego) so I'm invariably going in the slip in reverse. It seems I have to get the revs pretty high before the centrifugal force to open the blades overcomes the forward motion that's trying to close the blades. This is pretty subjective. I've borrowed a friend's Go-Pro camera, and I hope to stick it in the water facing the prop so I can verify what I think is happening is what's happening.

[Mike McDonald]

Clay and Mick,
Thanks for the feedback and photo.  The boat just went in the water, with the fixed prop, so I won't be able to put the FlexoFold on until haul out.  That will give me more time to learn about other C-34 owners experience with a 15x10 prop.  At least now I know what I have.  Thanks again.
Mike......

[Noah]

FYI- Changing props in the water is no big deal. I used to do it regularly when delivering race boats back "up wind". Don't let that factor too greatly in your decision-making.

[Noah]

To clarify my "no big deal" statement: this assumes you have SCUBA gear and a prop puller (which I have). Otherwise you will need to hire a diver, but this should be an easy, inexpensive job for them.  Also, I recently got a quote from Flexifold. They recommended a 15 x 11 for my boat (Universal 25XP). The cost was $1,100! I have not yet taken the plunge (to purchase)

[Stu Jackson]

As you may imagine, this prop has been discussed on this forum for many years.  I suggest you search on read previous posts about pitch and diameter before you make a purchase or set one up.  Many of our skippers have "been there, done that" so you can avoid reinventing the wheel.  Good luck.

[Noah]

Just passing on what the factory was recommending. Right or wrong. I haven't made a decision to purchase and plan to do due diligence on Forum and elsewhere prior to. My point was changing (most) props in water is not that tough--and that these props are expensive!

[Stu Jackson]

Noah, FYI, as you can also imagine, there are discussions about these types of props over on the C36 Forum, too.  In many cases, the "factory", and I'm assuming here that you mean the prop factory, not Catalina, has suggested what experienced skippers have already learned is the wrong prop...   I agree with you, do your due diligence.

[Noah]

One last post on this, just to clarify. The 15x11 recommendation from Flex-O-Fold Denmark, was for their 2-bladed folding prop.

[Clay Greene]

I wouldn't use a two-blade Flexofold on a M35 engine as a benchmark for the right pitch on a three-blade Flexofold on a boat with a M25XP engine. Here is what the sales representative told me in response to my question on this topic:

Those two engines are 23 HP and 30 HP respectively.  The reduction ratios are also different, resulting in a bit of difference in shaft/prop RPM. On the M35 I would recommend a 15 x 11 2-blade or a 15 x 10 3-blade. Flexofold sizing is generally +1" in pitch compared to a fixed prop, as our blade shape is more sophisticated and manufacturing tolerances are tighter. It's standard practice for us to subtract 1" of pitch moving from 2-blades to 3, in order to compensate for the increase in blade surface area and resulting change in efficiency.

[Noah]

I am little confused by your response. I have an 25XP engine for which Flex-O-Fold recommended at 15x11 two-blade folding prop. Do you not agrees with their recommendation?

[Stu Jackson]

I am little confused by your response. I have an 25XP engine for which Flex-O-Fold recommended at 15x11 two-blade folding prop. Do you not agrees with their recommendation?

That was my point earlier.  Regardless of what FoF recommends, research what other C34 owners with your engine have found that works.

[sail4dale]

I have a Flexofold 15 x 10 on my boat for over 11 years but even with my 35 HP engine I cannot get full RPM. 
This is not all bad as I get up to 2900 RPM before it smokes.  My cruising speed can be 7.3 with a clean bottom
but I usually run at 2500 and get good performance at 6.8 -7 knots.  .6 GPH

I love the prop .... backs down well and I have not seen any delay in it unfolding.  I replace the zinc
about 3 times a year. 

My question is:  with a 25 HP engine would not a 9 pitch be more appropriate?  It would get you up to
max RPM easier.

[Mike McDonald]

I really appreciate everyone's input on the FlexoFold prop.  I'm still a little uncertain if the 3-blade 15x10 is the right prop for an M25XP engine. 

If there are C-34 owners on the forum with this combination, I would love to hear about your personal experience with this prop.  Very interesting discussion.  Thanks.
Mike.....