Flexofold size for a 2007 B49 with Yanmar 75hp and ZF30M?

[boom23]

Hi all,

I am in the process of purchasing a 2007 B49 with the 75hp Yanmar engine (3000-3200 max rpm) and ZF30M (2.15F, 2.64R) and the stock (I assume) fixed propeller. The markings on the propeller are not visible.

During the sea trial, the boat reached 9kn at 3500rpm (assuming the Yanmar gauge is correct). The alternator is stock. She weighs 30,000lbs.

What is your experience on this?

Also, I would like to replace the stock fixed prop with a flexofold. Beneteau offered a 19x11 Flexofold (up to hull #87) or 18x13 (starting hull #88).

Flexofold person recommended 20x13 to reach 3000rpm or 20x12 to reach 3200rpm.

What do you think about flexofold propeller size? What do people use and what are the speed/rpm numbers?
What prop size should I get?

Thank you for any info.

 

[Bob846]

Re: Flexofold size for a 2007 B49 with Yanmar 75hp and ZF30M

Sounds like the tach is incorrect or the boat is very under-propped. Max HP is obtained at 3200rpm so you probably want to be running that engine around 2800-2900 RPM for the best efficiency.

I currently have flexofold on my B423 and also installed one on a 36CC. The hub is fairly universal for the given shaft size and you can mount most blade sizes on it. If you go with flexofold's recommendation and it does not work out, then flexofold should be on the hook for the haulout and blade replacement. If you go with the dealer's recommendation, then the same should apply to the dealer. I find flexofold is typically a little aggressive in pitch department. In my 10+ years of flexofold ownership, I'm very happy with the design's performance. I do notice more prop-walk in reverse, but I use this to my advantage most times.

 

[Ron20324]

Re: Flexofold size for a 2007 B49 with Yanmar 75hp and ZF30M

18,19,20 inches... you'll have to keep the prop a certain distance from the hull. I hope someone will chime in with the suggested clearance, or the dealer should know.

EDIT: I just found a book that suggest prop to hull clearance of 15%. So, for a 20 prop, you'd want 3 inches between it and the hull.

 

[boom23]

I think I got to the bottom of it... The following is from cruisersforum.com:

I have the oceanis 50 with a yanmar 4JH4-TE with a SD-50. Flex-o-fold recommended the 3-Blade 20x13L.
I installed it last spring and am very happy with it. I get 9.5 kts at 3200 rpm. but am generally cruising at 6.5-7 at 2000 rpm.

----------

The SD50 has 2.32 reduction ratio forward and reverse. Since the ZF30M has 2.15 reduction forward, the 20x13-3L will not allow the engine to reach 3200rpm.

I used a prop calculation program to figure out the difference in prop size/pitch between 2.32 (SD50) and 2.15 (ZF30M) reductions.

The difference is only 1" in pitch.

So, it seems that the Flexofold people recommendation for a 20x12-3R will be just right to achieve 3200rpm with the 2.15 reduction ZF30M!

In addition, hull-propeller clearance should, hopefully, be OK since the factory has the 20x14 flexofold as an option for the B49 with the 110hp engine.

This is what I have so far...

 

[boom23]

Sounds like the tach is incorrect or the boat is very under-propped. Max HP is obtained at 3200rpm so you probably want to be running that engine around 2800-2900 RPM for the best efficiency.

I have not verified the tach, but I believe that it is correct since the alternator/engine/instrument is stock. I am hoping that another B49 owner will have some info on the B49 stock fixed propeller with the 76hp engine.

 

[Grouperhound]

I bought a Flexofold last spring for my 45. They recommended a 13 pitch, and my calculations came up with 13.5. In fact I now run about 100 to 150 rpm over the recommended WOT max, which I don't use of course, suggesting that a little more pitch as my calculations indicated would have brought it to spec. My point is that they were very close. I might have actually gone for a 12 pitch but I'm comfortable with the 13. It's the exact option that Beneteau offers from the factory, and I'm still under warranty. ;-) Yanmar prefers the RPM to be slightly higher as opposed to lower.

The calculation I got for you was exactly 12 inches of pitch.

10,750 inches/min(boat speed of 8.9kn) / 1490rpm(prop speed) / 60% = 12.0

 

[boom23]

I bought a Flexofold last spring for my 45. They recommended a 13 pitch, and my calculations came up with 13.5. In fact I now run about 100 to 150 rpm over the recommended WOT max, which I don't use of course, suggesting that a little more pitch as my calculations indicated would have brought it to spec. My point is that they were very close. I might have actually gone for a 12 pitch but I'm comfortable with the 13. It's the exact option that Beneteau offers from the factory, and I'm still under warranty. ;-) Yanmar prefers the RPM to be slightly higher as opposed to lower.

The calculation I got for you was exactly 12 inches of pitch.

10,750 inches/min(boat speed of 8.9kn) / 1490rpm(prop speed) / 60% = 12.0

Grouperhound,

Thank you for the info. What about the diameter? Is 20" the correct diameter?

I just want to make sure because the factory sells 19x11 and 18x13, which are way undersized.

 

[Grouperhound]

My saildrive came with an 18 and thats what I replaced it with. I assume yours came with at a 19.?? I was in the same boat as you, I really didn't know what I had. If Flexofold is recommending the 20 then I assume that is the correct size. I don't think a 20 is unreasonable. Their sizes are 12,13,14,15,16,17,18,20. It doesn't look like they have a 19, so it's likely they are taking it up to the next size, rather than down. I read in another thread that Flexofold recommends the same prop for the 473.

 

[boom23]

Re: Flexofold size for a 2007 B49 with Yanmar 75hp and ZF30M

Thank you again. From what I have heard, Flexofold is pretty accurate in selecting a prop size. I will order the 20x12 prop, as they suggested.