Flexofold Prop Size ? Y4JH4E Hunter 41

[TFlight]

I'm considering a Flexofold Prop for my 07 Hunter 41DS.
Current configuration:
Engine: Yanmar 4JH4E 40.5kw (54.3hp) @ 3000rpm 36.8kw (49.3) @ 2907rpm
Gearbox: Touff Torq by Kanzaki model KM35A2 with ratio 2.33 forward & 3.06 reverse.
Fixed 3 Blade prop 18" X 12" I'm not sure if my tachometer is off or I'm under proped but I have seen 3200rpm with this fixed propelled.

Here's the question, does anyone have a Flexofold prop with this configuration and if so what size?
Can I over stress my engine with too large a prop? I'm a little concerned with the recomomdation and procedure of Flexofold 20x13-3R prop. Would it be safe to operate as recommended by Flexofold without negatively affecting my engine of fuel performance?

Flexofold has a suggested a 3-blade 18x14-3R but seems to prefer the 20x13-3.
This is there reply:
A 4JH4E, has max. 54HP/3000RPM ( gear reduction ratio 1:2,33/1:3,06 ) we would recommend a 3-blade 18x14-3R propeller for your Hunter 41DS – though if you would like to perform better in reverse we would recommend a 3-blade 20x13-3R this will though cost you approximately 200RPM in forward.
With the bigger prop 20x13-3R it will improve your maneuvering in reverse, but you will not be able to go above the RPM of approximately 2800RPM in forward. With a 20x13-3R you will reach a higher speed at a lower RPM. You will not strain the engine as long as you don’t try to push it above the app. 2800 RPMs in forward.
With a 18x14-3R you will be able to reach the max. 3000 RPMs.

Thanks,
TFlight

 

[Mikem]

I had an 18 x 17 3 blade fixed and they recommended a 22 x 14. A friend of mine had the same boat, engine, and tranny with a 20 x 14 three blade flexofold. It achieved hull speed plus a couple of tenths, maneuvering was fine and reversing was no problem all at rated RPM. I opted for the smaller diameter of 20 rather than chancing it with the 22 diameter recommendation.

 

[Don Lucas]

I'm considering a Flexofold Prop for my 07 Hunter 41DS.
Current configuration:
Engine: Yanmar 4JH4E 40.5kw (54.3hp) @ 3000rpm 36.8kw (49.3) @ 2907rpm

A 4JH4E, has max. 54HP/3000RPM ( gear reduction ratio 1:2,33/1:3,06 ) we would recommend a 3-blade 18x14-3R propeller for your Hunter 41DS –

My 410 has the same engine and I've had the 3 blade 18x14 on it for 5 years.

 

[TFlight]

My 410 has the same engine and I've had the 3 blade 18x14 on it for 5 years.

I take it you are satisfied with your 18x14 Flexofold and receive equal or better performance in cruise, stopping, reverse?

 

[Don Lucas]

I take it you are satisfied with your 18x14 Flexofold and receive equal or better performance in cruise, stopping, reverse, and maneuverability?

I'm satisfied with it's performance. But have no idea what you mean by cruise/stopping/reverse/maneuverablity! I didn't get a FlexOFold to do any of those things, I got it to increase sailing performance. It cruises fine and with clean hull and calm seas I've done 9 knots, and it stops and backs fine far as I'm concerned.

 

[Mikem]

I agree with Don on the stopping maneuvering bit. I saw no appreciable stopping or maneuvering performance difference from my 3 blade fixed prop but I did get better sailing and the shaft didn't spin when the blades folded. Hence no wear on the tranny and no noise either. I have always wondered about the emphasis on stopping or reversing. Maybe that is just marketing hype.

 

[TFlight]

I thank you Mikem & Don Lucas for your feedback.

Of course I'm looking at switching from a fixed prop to the Flexofold prop to alleviate the bucket of drag I'm towing around under sail and if it minimizes prop walk (prop wash) that may be an added benefit too. As all feathering or folding props are not made equal and come with their own set of pros & cons I'm trying to make the best choice as not to sacrifice the primary job of any fixed propeller and that being to propel the boat efficiently under power, stop quickly, minimize strain on the engine while most importantly being predictable and reliable.

I have pretty much decided on the Flexofold Prop partly based on the March 24, 2015 Yachting Monthly magazine article http://www.yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807 as well as other research.
The final decision I need to make, (not counting explaining how much $$ I spent to the Admiral

) is which of the two factory recommended sizes should I chose to replace my fixed 18x12 prop with, the 18x14 or the 20x13. At this point I am leaning towards the smaller & less expensive 18x14.

Again thank you for your information and input.

 

[Don Lucas]

BTW - on my last boat I had a 3-blade feathering MaxProp. These are suppose to be better in reverse and have less prop walk than the folders. Far as I'm concerned the Flex-O-Fold folding unit is at least as good in reverse as the MaxProp was, has less maintenance and is simpler, and was around $1000 less expensive.

 

[Sailgunner]

Flex-o-fold sized and sold me a prop that was too big. I could not get full RPMs out of my engine. Yanmar told me I was hurting my engine because the prop was putting too much torque on the engine. I was getting good cruising speed but only max rpms of 3000 vs 3600 rated rpms.
So I went back to flex-o-fold and they refused to replace my blades. I bit the bullet and bought the new blades and I can now get back to the max 3600 rpms. I usually cruise around 3000 to 3200.
I have a 50HP 4Jh2E with a Kanzan KM4A transmission. The correct prop for my boat is a 17x12-3R. The first one Keld sold me was 18 x 13 RH 3-blade .
I like the prop for many reasons but still not happy the replacement blade cost of $1100 when Flex-o-fold screwed up, not me.
So my caution is this. After you get your new prop go out and run it and make sure you can get up to your rated max RPMs. If you cannot send the prop back and have them resize the prop.

 

[TFlight]

Flex-o-fold sized and sold me a prop that was too big.

Good info Sailgunner. That's exactly what I'm afraid of so I think I will go with the smaller 18x14 3blade prop.

 

[dakno]

I recently installed a 18' Max prop feathering. Several skippers in my marina advised against folding props. The performance is impressive vs the original fixed 18 x 12, especially in reverse. A very good thing about these props is the pitch can be easily changed if you want to experiment. Having done several prop/pitch changes over the years in various boats it seems to me that if you are under proped you will over rev., conversely, if you are over proped you will under rev..

 

[Don Lucas]

My 410 has the same engine and I've had the 3 blade 18x14 on it for 5 years.

I was cleaning my prop today and was wrong. I have a 3-blade 18X13 prop.

 

[TFlight]

I seem to be slightly under proped now, base on the rpm's of my fixed 18x12 3 blade prop. I didn't want to over do it so I went with the smaller of the two recommended Flexofold props, the 18x14-3 as opposed to the 22x13-3. I just place the order the other day. I hope I'm pleased with it in all phases of sail & power. I should know in a few weeks when I'm back in the water.

 

[seadaddler]

I was told back in 2008 by Flex O Fold I could return the blades if they were wrong size as long as I did not damage or paint them.
What I did was check with other same boat owners in this forum and see what prop size they had because my stock prop was all wrong.
My flex o fold prop is great and does everything it is suppose to do and does it very well sailing,motoring,backing up and very much improved my boats performance greatly.
With my old prop I could hardly reach 6 knots and now I do 6 1/2 to 7 knots no problem.
Nick

 

[discovery]

They did the same to me, I have a passage 456 with the 4 jh3te 75 hp yanmar, a yr after I put the prop they reccomend eg on I noticed some blue smoke, my diesel mech asked my top rpm, I told him 3300 he said I was over propped, Flexofold said my engine was underperforming, I had a compression ck recently and that was fine, looked into having the pitch changed but no one will touch it, flexfold says to bad, I dident know about the new blade option?

 

[Sailgunner]

They did the same to me, I have a passage 456 with the 4 jh3te 75 hp yanmar, a yr after I put the prop they reccomend eg on I noticed some blue smoke, my diesel mech asked my top rpm, I told him 3300 he said I was over propped, Flexofold said my engine was underperforming, I had a compression ck recently and that was fine, looked into having the pitch changed but no one will touch it, flexfold says to bad, I dident know about the new blade option?

They kept denying they made a mistake. Finally I ask if I was to go down one size what would it be. Keld then told me and how much it would cost - $1100. I bit the bullet and as I stated I now have the correct size prop. I still have my old blades if anyone needs them. I love the prop but would never do business with this company again.

 

[TFlight]

I seem to be slightly under proped now, base on the rpm's of my fixed 18x12 3 blade prop. I didn't want to over do it so I went with the smaller of the two recommended Flexofold props, the 18x14-3 as opposed to the 22x13-3. I just place the order the other day. I hope I'm pleased with it in all phases of sail & power. I should know in a few weeks when I'm back in the water.

Just a follow up on my Flexofold prop.
I did install the 18x14-3 blade prop on my 07 Hunter 41DS and I am very happy with that choice.
The new prop did bring my WOT RPM's back from 3100 rpm to 3000 rpm where it should be for the Yanmar 4JH4-E.
Boat speed through water under power has also increased slightly.
A few of the RPM's and "Boat Speed's" I've noted are:
2.6 kts = Idle forward
5.0 kts = 1300 rpm
6.0 kts = 1600 rpm
6.5 kts = 1800 rpm
7.0 kts = 1950 rpm
7.5 kts = 2200 rpm
8.0 kts = 2400 rpm
Sorry I don't have data for higher RPM's up to WOT of 3000 RPM's but next time I have smooth seas I will try and remember to note those too.

My sailing boat speeds (speed through water) has increased, my guess is anywhere from 0.25 to 2.0 kts.
We now can sail in lighter winds and the boat accelerates better as well.

I might need to dive and clean the prop or change the way I transition from power to sailing because occasionally the prop shaft will be spinning very slow. This has only happened a few time that I've noticed. I put the transmission in reverse for a few seconds and back to neutral and the rotation stops.

A not of caution, when approaching the dock or mooring area under power remember to go to neutral early as your boat will not decelerate like it did with the fixed prop.

So far very happy with the switch from fixed to Flexofold.

 

[Rick486]

Interesting. Just about identical to my boat, 44DS, same engine maybe a bit longer waterline. I have an 18 inch maxprop. I have done some calibration lately which shows the Yanmar tach reads about 50-75 RPM high in comparison to measured RPM with an optical device. In calm seas we run about 2350-2400 good for 7.8-8.2 knots depending on wind, etc.
Update: just noticed in your OP that your gearbox is different from mine. I believe mine is a 1.6 ratio.

 

[TFlight]

Just a follow up on my Flexofold prop.
I did install the 18x14-3 blade prop on my 07 Hunter 41DS and I am very happy with that choice.
The new prop did bring my WOT RPM's back from 3100 rpm to 3000 rpm where it should be for the Yanmar 4JH4-E.
Boat speed through water under power has also increased slightly.
A few of the RPM's and "Boat Speed's" I've noted are:
2.6 kts = Idle forward
5.0 kts = 1300 rpm
6.0 kts = 1600 rpm
6.5 kts = 1800 rpm
7.0 kts = 1950 rpm
7.5 kts = 2200 rpm
8.0 kts = 2400 rpm
Sorry I don't have data for higher RPM's up to WOT of 3000 RPM's but next time I have smooth seas I will try and remember to note those too.

My sailing boat speeds (speed through water) has increased, my guess is anywhere from 0.25 to 2.0 kts.
We now can sail in lighter winds and the boat accelerates better as well.

I might need to dive and clean the prop or change the way I transition from power to sailing because occasionally the prop shaft will be spinning very slow. This has only happened a few time that I've noticed. I put the transmission in reverse for a few seconds and back to neutral and the rotation stops.

A not of caution, when approaching the dock or mooring area under power remember to go to neutral early as your boat will not decelerate like it did with the fixed prop.

So far very happy with the switch from fixed to Flexofold.

I had a chance to get some boat speed results at wide open throttle this past weekend. The water was relatively calm. At wide open throttle I'm achieving 2950 RPM as indicated by the factory installed tachometer. Earlier in the season with a clean haul I was able to achieve 3000 RPM but the boat speed meter wasn't working then.
8.8 to 8.9 kts = 2,950 rpm wot

I am concerned that after 3 minutes the over heat alarm came on. I immediately reduce the RPM's and the temperature came down. This year I replaced the impeller (the old one still look good) just inspected the pickup screen and it is clean. Maybe the seawater pickup is dirty although I don't see much growth on the sides of the boat. I guess I will have to dive down and check it out. I hope that's all it is. The engine only has 640 hrs in it. I do believe Yanmar recommend running the engine at wide open throttle 1% of the time. Has anyone else had this problem?

 

[Mikem]

Have not had the problem but if you habitually ran the engine at a reduced RPM you may have some build up. A Rydlyme flush would clean it out.