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Post by zaphod on Jun 25, 2019 16:31:40 GMT
So far we have been quite happy with the performance of our 39i, however, I still feel like there is quite a bit more performance to be had out of her, particularly in lighter wind, which is very common in our waters.
We are currently dragging around a 3 blade fixed prop, and I really think it is holding me back in a big way, so I am contemplating a low drag prop for our next upgrade.
I have read the comparison test done by Yachting Monthly, and there is a lot of interesting information, but the data is still limited to one specific boat model.
The problem is we are also very happy with the boat's performance under power, and I would hate to reduce that significantly. Currently we cruise at 7.5kts @2500rpm and 8.5kts @ 3000rpm. Of course reverse performance is phenomenal as one would expect out of a fixed prop.
I am leaning towards the Flexofold 3 blade based on cost, simplicity, and reputation. I realize that I will be sacrificing some stopping power in reverse, but if YM's test results hold true forward performance could actually improve.
I am wondering if anyone else made the transition from fixed to folding on the same boat, and what their observations were. I would like to hear about any low drag props, not just FoF.
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Post by Don Reaves on Jun 25, 2019 17:09:55 GMT
I put a KiwiProp on my SO35 more than 10 years ago. Half the cost of most folding and feathering props. Incredibly simple and easy to maintain, since it has no gears and doesn’t need antifouling (the blades are composite). The YM article rated its forward thrust lower than most, but I didn’t notice when I replaced my two-blade fixed prop. Reverse thrust is phenomenal, with just enough prop walk to be helpful when maneuvering into dock.
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Post by MalcolmP on Jun 25, 2019 17:31:50 GMT
Our 39i has had an Autoprop for past 11 seasons, not cheap, but performs amazingly under sail and power. Maintenance is simple and should never wear out, other than maybe changing out the bearings , that said have not changed them for maybe 7 seasons and first set think I hadn't greased correctly.
Lots and lots of opinions out there on merits of various feathering and folding, but all will improve sailing compared with fixed, typically by at least 0.5 knots. The downside of all models is that you are introducing moving parts so will need some maintenance and can lead to wear in the long term, that's one of the reasons I still love my Autoprop, no reason it will not outlast me...
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Post by Tafika II on Jun 25, 2019 18:25:32 GMT
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Post by zaphod on Jun 25, 2019 18:55:35 GMT
Thanks for the link! That's an interesting discussion. It looks like Flexofold has a huge variety of options. Given that they are the OEM prop supplier for Jeanneau, and the fact that there are so many boats like mine on the water I would think they have sizing pretty well figured out.
This is what they quoted for my boat:
With a Yanmar 3JH4E ( max. rated 39 hp / 3000 rpm, gear reduction ratio 1:2,33 ) we would recommend a 3-blade 17X13-3R propeller for your Jeanneau Sun Odyssey 39i.
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Post by johannes on Jun 26, 2019 9:01:27 GMT
We switched from the original 2-blade fixed to a 3-blade Flexofold this spring on our SO 37. The difference is very noticeable in a positive way. First of all, the vibrations we had previously are now gone in the entire RPM range. Extremely smooth. It also has better bite going forward. Reverse is a bit worse, meaning we need a bit more thrust. It is not a problem in practice.
The improvement in sailing performance is hard to quantify since we also have new sails + new backstay tensioner. But in general we are very satisfied with the Flexofold.
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Post by Caxton on Jun 26, 2019 16:25:49 GMT
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Post by zaphod on Jun 26, 2019 18:10:17 GMT
I switched from a 2 blade Martec to a 2 blade Gori on my last boat. It definitely had better reverse than the martec. It was a little under sized for my boat so forward speed was actually a bit slower. ( I bought the prop used). It was a very reliable prop, and never failed to open when reverse was needed. I think that is one of the things that concerns me about feathering props...the chance that the blades do not rotate properly for reverse is greater than the folders not opening. There is just more to go wrong with feathering props.
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Post by Don Reaves on Jun 26, 2019 20:30:00 GMT
I think that is one of the things that concerns me about feathering props...the chance that the blades do not rotate properly for reverse is greater than the folders not opening. There is just more to go wrong with feathering props. Curiously, I have the opposite opinion, at least for my KiwiProp. The blades switch due to water flow when going into reverse, rather than relying on the centrifugal effect. Dead simple and always works.
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Post by rene460 on Jun 27, 2019 1:24:39 GMT
I have the Autostream feathering prop, bought six or seven years ago. Every time I start the motor, I test the operation on forward and reverse before I drop the ropes. It is my commissioning engineer history. The only time it has not worked properly, it was fouled with weed, a normal hazard at that particular location.
Each annual haul out, I check the operation, and put in a few shots of the recommended grease until the grease appears at the expected spots, in addition to the normal clean and prop speed application.
Any prop with moving parts will require more maintenance than a fixed prop. My shipwright has had several gori props come in with barnacles in the gears, which are not enclosed like the Autostream. I suspect that these problems are more about lack of use than a fundamental problem of the design, as others have used them for years without reported issues.
I moor in a pen, and as my twin rudders give no steering at slow speed, I have to approach with speed for steering, especially in a cross wind. It takes courage and confidence that the prop will operate to give good stopping power. It has not let me down.
A propellor is an appendage which will always create some drag, regardless of the hull it is attached to. You can rely on those YW tests results as a relative indication of how much drag different propellors cause, though the drag will vary with prop size. As they were all tested on the same boat, presumably they were all about the same size, allowing for some comparison between designs. However it is easy to see in that report that the big difference in drag is between fixed propellors and the rest. Folding are slightly better than feathering ones with respect to drag if you are into racing and want least drag no matter what, feathering ones may be a better compromise if reverse thrust is also important to you.
Remember also that this drag varies with speed through the water, so the effect on boat speed also varies with boat speed. Don’t expect a half knot improvement if you are in light winds and only going one knot with your fixed prop. As the boat drag also varies with boat speed, I am not sure if the propellor drag is the same proportion of the total speed at low speed or not. But probably a reasonable assumption for the purpose. However at higher speed, as you try and force the boat above that natural hull speed, the boat drag increases much more rapidly, while the propellor drag is closer to just proportional to speed squared (roughly), so becomes less important compared with hull drag. And of course most of us have no idea of the magnitude of the hull drag anyway.
There are many reports for each of the propellors where owners have found better or worse performance than the fixed prop they replaced. I suspect this is more about how well the replacement propellor matches the hull and engine requirement than about the design itself. Though it must be remembered that after diameter and pitch, blade area is probably the next most important factor in propellor thrust development. You cannot expect the same performance from a two bladed prop, folding or otherwise, that you will get with a three bladed fixed prop with blades that fill most of the circle, but it will have less drag. And a propellor that relies on centrifugal force to open the blades will not work so well in reverse when the thrust is opposing that opening action. Modern designs seem to be overcoming some or most of this limitation, so may only need a few extra rpm which is not really an issue in reverse.
With a fixed pitch propellor, you are reliant on the manufacturer to give you the proper selection but it is worth perusing old forum posts to see what others have used, as a check on what you are being offered. With my feathering propellor, there are separate adjustable stops on forward and reverse, so you can play with these to tweak the performance if you feel it necessary. If you are a confident diver, it may be possible to do this in the water, but for me, it is a case of one opportunity per year to make a small adjustment and then see if it seems better or worse. As my propellor properly loads the engine at full open throttle, and stops me reliably when I enter the pen, I have never felt the need to fiddle with the manufacturers settings. If I had started when I first bought the prop, it would surely be perfect by now!
It is well worthwhile to spend some time reading old forum posts on the topic, as there have been many. They are timeless and each sheds light on a slightly different aspect. Together they are a mine of valuable information.
rene460
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Post by dslittle on Jul 1, 2019 9:03:58 GMT
I have a Gori 3 blade and I am very happy with it. I am surprised at the results of the YM test as I believe it works well (especially in ‘overdrive’ mode where I get 5kn at 1500rpm). It definitely gives me at least 0.5kn extra when sailing. All in all it was a very good change five years ago.
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Post by zaphod on Oct 11, 2019 23:21:00 GMT
Well, after participating in a couple of fun races in light wind, and tearing my hair out wishing for more boat speed, I finally pulled the trigger on a new prop. I ended up buying a Flexofold 3 blade. After researching and reading articles it seemed like a good choice. I am looking forward to getting the prop installed and testing it. I ordered it from Flexofold in Denmark on Tuesday, and it arrived on my doorstep Friday!
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Post by sitara on Oct 12, 2019 21:35:35 GMT
Zaphod, you will be delighted with the difference, better boat speed and better pointing ability. I fitted a feathering prop (Autostream) to my SO36i and got far better sailing performance but lost a bit of motoring speed compared to the old fixed and over pitched original prop.
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Post by zaphod on Oct 12, 2019 22:19:55 GMT
Zaphod, you will be delighted with the difference, better boat speed and better pointing ability. I fitted a feathering prop (Autostream) to my SO36i and got far better sailing performance but lost a bit of motoring speed compared to the old fixed and over pitched original prop. I sure hope so! The testing and anecdotes I have heard actually show an improvement under power with the Flex-o-fold vs a fixed prop. Hopefully that holds true as well!
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Post by vasko on Oct 13, 2019 4:02:52 GMT
Folding prop is a great addition I enjoy my one greatly - although I went with the cheaper Elice-Radice 2B 17x13 RH 25mm for my 9.98 (Sun Liberty)
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Post by zaphod on Oct 31, 2019 3:37:48 GMT
Well I installed the new 3 blade Flexofold prop today. It was quite simple to install, and I am really impressed with the design. The gears are protected from getting fouled by barnacles and mussels, (unlike the Gori on my last boat), and all but one of the screws is also protected from getting clogged with growth. That is something you appreciate years down the road when you have to take the prop off and you don't have to dig out each setscrew! It also appears that it is virtually impossible for the blades to come off accidentally even if the pin retaining screws come loose because it is impossible for them to back all the way out. I also noticed that the prop automatically closes itself by gravity alone, so no matter how light the wind you can be confident it will be fully closed. I am looking forward to testing it out when the boat goes back in the water next week!
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Post by andreshs1 on Oct 31, 2019 7:11:29 GMT
Hi Zaphod
I totally agree
I got mine fitted last week and I could immediately tell the difference on performance and reduction of propeller walk
so far I am loving it
cheers
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Post by alenka on Nov 2, 2019 8:11:48 GMT
I would be interested to learn if you find increased vibration levels at high power settings?
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Post by andreshs1 on Nov 2, 2019 10:46:31 GMT
Hi Alenka
Today we motored for 1 hour at 2800rpm no issue and normal vibrations
Cheers
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Post by zaphod on Nov 16, 2019 1:09:23 GMT
Well, I just splashed the boat today and motored her back to the yacht club with the new prop....first impressions? WOW! What a huge improvement in performance! The ZF fixed prop gave me 7.5kts @2500rpm and 8.7kts at full throttle. The new Flexofold gave me 8.4kts@2500 and 9.7kts at full throttle! That is quite an improvement! I am looking forward to getting out sailing to see what speed improvement I get then. I have no doubt it will be very noticeable.
Money well spent!
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Post by Tafika II on Nov 16, 2019 1:55:23 GMT
When sailing we put the gear in reverse to prevent the prop from opening and the shaft from turning.
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Post by so36idavid on Nov 16, 2019 6:28:50 GMT
Tafika, I have the flex-o-fold on my 36i. I put it into reverse when I start sailing which stops the prop. Then I put it back into neutral so I don't start the engine in gear. Once it's stopped it won't unwind itself and start rotating again. Don't ask me how I learned to do that . David
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Post by MartyB on Nov 16, 2019 18:07:54 GMT
Did you do a bottom paint too?!?!? not saying the prop was the speed gain, but I find new bottom paint nets me .5-1 knot depending upon the how dirty the bottom was before the haul out.
Those are good gains none the less.
Marty
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Post by zaphod on Nov 17, 2019 17:49:07 GMT
Did you do a bottom paint too?!?!? not saying the prop was the speed gain, but I find new bottom paint nets me .5-1 knot depending upon the how dirty the bottom was before the haul out. Those are good gains none the less. Marty I did put a fresh coat of bottom paint on, but only because the boat was on the hard anyway. The bottom was not at all fouled when it came out of the water.
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Post by NZL50505 on Nov 21, 2019 3:33:45 GMT
That’s an impressive speed increase (assuming like-for-like comparison). I’m still musing moving to a 3B Flexofold as well but have kind of got used to my crappy folding Volvo which has taken the initial urgency away.
The 9.7kts fig sounds like a bit of over-reading given your hull speed is about 8kts. It’s quite common to get slightly over hull speed under power with a modern engine and clean hull & prop... but probably not by quite that much 😊
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