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Post by andreshs1 on Jun 20, 2018 5:02:17 GMT
Hi Sitara
Thanks for the info!
Regards Andres
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Post by snwl on Jun 20, 2018 7:14:09 GMT
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Post by andreshs1 on Jun 20, 2018 11:33:10 GMT
Hi snwl
Thanks for the link I was looking at the same but printed version 🙂
Cheers
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Post by bratwurzt1 on Jun 21, 2018 1:52:29 GMT
PYI that sells Max are incredibly helpful and do all the calculations for you. If they are not open they will always return a call, couldn’t be more happy with customer service.
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Post by andreshs1 on Jun 21, 2018 4:31:03 GMT
Hi brat
Based on the feedback I got so far there is a concern on my gearbox ratio, as apparently the standard is 2.63, yet mine is 2.15
Anyone with the same gearbox as mine?
Cheers
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Post by markclement on Jun 21, 2018 7:09:24 GMT
Hi brat Based on the feedback I got so far there is a concern on my gearbox ratio, as apparently the standard is 2.63, yet mine is 2.15 Anyone with the same gearbox as mine? Cheers Hi That still sounds weird as I think as said in the thread before that your forward ratio is 2.15. For eg I have a 4JH110CR Yanmar on a Jeanneau 51 - the Gearbox is a ZF30M - Mechanical wet maliple clutch - Ratio forward 2.15; Ratio reverse 2.65 So I conclude you have a very robust / capable gearbox if you have the same ZF30M with a 55HP. Also my shaft speed (and therefore propeller speed) at max power is 1,444rpm in forward and 1,176rpm in reverse as per the specs and yours should be the same. The only difference will be in the propeller (mine 3 blade folding Flexifold) due to the difference in motor power (mine 110HP) and hull speed (mine 9.2Kts) and usual hull weight loaded (mine about 16.5 tonne). Your 3 blade will be the only different aspect I believe with a different size and pitch. Cheers
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Post by andreshs1 on Jun 21, 2018 13:23:23 GMT
Hi Mark
Brilliant, thanks for the confirmation!!
both, Autoprop and Flexofold agents asked me to double check as the 'standard' is 2.63
But thanks, it makes me more comfortable knowing that the figures I provided are correct
Regards Andres
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Post by markclement on Jun 21, 2018 21:57:15 GMT
Hi Mark Brilliant, thanks for the confirmation!! both, Autoprop and Flexofold agents asked me to double check as the 'standard' is 2.63 But thanks, it makes me more comfortable knowing that the figures I provided are correct Regards Andres Hi Andrés Of course to be 100% sure the identification plate attached to the gearbox will give you the model, serial number and ratios - the higher ratio being reverse Cheers
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Post by wellmax01 on Oct 22, 2018 23:45:12 GMT
Hi NZL8970 just curious to see how you got on with your prop selection. I know your boat (we nearly bought it years ago) we now have the same model 42ds located at Gulf harbour marina , on the same finger!
We too have a Volvo folding prop which is garbage in reverse. I think this is a common problem with this prop. Anyway it’s started clattering and vibrating so needs replacement. Flexofd received positive reviews in a group test some years back and I think we will go that way. There is some debate about the 18 or 20” selection however i’m keen to hear from you if you’ve made the change?
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Post by hoppy on Oct 23, 2018 3:24:14 GMT
Hi NZL8970 just curious to see how you got on with your prop selection. I know your boat (we nearly bought it years ago) we now have the same model 42ds located at Gulf harbour marina , on the same finger! We too have a Volvo folding prop which is garbage in reverse. I think this is a common problem with this prop. Anyway it’s started clattering and vibrating so needs replacement. Flexofd received positive reviews in a group test some years back and I think we will go that way. There is some debate about the 18 or 20” selection however i’m keen to hear from you if you’ve made the change? Just email Flexofold with your boat/engine/gearbox details and go with what they recommend. No need to debate the prop size.
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Post by super g on Oct 24, 2018 6:15:07 GMT
Look at www.simplicity-marine.com/pdf/ZF/ZF_30_M.pdf. It appears that the ratios given are for the A position (forward - continuous running) and the B position is reverse. The forward ratio is the one the prop designer will want. I’d recommend a feathering over a folding. I had a max prop on the previous boat and it was brilliant and had the advantage of the pitch being adjustable and going into forward or reverse was a smooth operation. I’ve a folding flex of old on this boat and it’s ok but needs a lot of revs in astern and makes a nasty clunk when stopping at any speed. The other type is the bruntons auto prop which works by witchcraft, my mate has one and has fitted a shaft brake as even I gear it has a habit of spinning under sail and creating a lot of drag and making the steering really heavy- this may be due to the type of gearbox that relies on hydrolic pressure for the gearchange.
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Post by ales on Apr 6, 2019 17:17:42 GMT
Hi,
I am also considering buying a 3blade Flexofold for my SO 43DS.
Two thing that concerns me: 1.) reverse. My neighbour said that he has to give more RPM when going in reverse (Beneteau 42CC, 3blade FF). And "more" is like 3000rpm.. That is a lot! 2.) what is the benefit in light winds (up to 13kts) with full sails up?
I know especially the last one is tough but if someone remembers the difference between old (fixed) and new (folding)? Sailors are speaking of 0,5 to 0,8 kts advantage...
Thanks...
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Post by rene460 on Apr 7, 2019 12:07:04 GMT
Hi Ales, You have added to a long running thread and I assume you have read all the replies above. If you browse other threads you will find more in a similar vein.
That YW magazine report is the best I have seen still, even though it was from 2009. It gives you all the information you really need about the difference between different propellors and is well worth reading and spending some time studying the results graphs. Use the link given earlier in this thread, or I see it is available as a link on the Flexofold and other manufacturers sites.
While your question is often asked, it is not really answerable, as there is no direct relationship between propellor characteristics and boat speed. Basically a propellor produces thrust, the hull experiences drag when it moves through the water, and the speed achieved is the speed where the propellor thrust equals the hull drag. The propellor thrust developed also varies with the speed it is moving through the water.
When sailing, the propellor adds drag to the hull so you go slower. But the drag of the propellor varies roughly with with speed squared. The hull resistance in the displacement range also varies with hull speed squared. If you use that YW drag data to plot two additional curves, one the hull drag plus the fixed propellor drag, and the second, the hull drag plus a folding or feathering propellor of your choice, you will see from careful reading of these curves that the speed difference due to different propellors varies with hull speed.
While those curves are for a different boat, the form is very similar for all boats in the displacement range. If you change the scales to percentages so that say 7 knots is 100% speed, and 130 kg is 100% drag, (you can see on the graphs where I got those figures from), the same percentages will be a good estimate for your boat. You actually don’t need to know what 100% drag would be in kg for your boat, but you probably do know roughly the 100% speed figure. Also, I suggest you ignore the stopping distances, the important figure is that bollard pull in reverse.
It it is possible that your friends Beneteau has an early folding prop which suffers from reluctance to open in reverse as the water force on the blades is tending to hold it closed, or could have barnacles or weed inhibiting it’s opening in reverse. Worth doing Vasko’s experiment and putting a GoPro on a stick to see if the blades are opening properly. Most manufacturers now seem to have overcome this problem, as you can see from the YW results.
As an example, I have an Autostream feathering prop on a hull with twin rudders. Minimal prop walk. Stops us easily in half a boat length at the speed we have to enter the pen to retain steerage without excessive revs in reverse. We have never had the need to slam it into reverse at 6 knots, but the test report had to have some parameters for comparing the different propellors. The actual stopping distance just depends on the prop thrust, hullspeed when you select reverse and the hull mass, and you will normally only want to stop from relatively slow speeds. That is why I say the bollard pull is the main one to study for performance in reverse.
rene460
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Post by ales on Apr 7, 2019 12:37:35 GMT
Thank you rene460 for your comprehensive answer.
I've read (probably) all the post regarding folding props and also that YM test.
I am aware that it is a tough question what will a folding prop bring you and only I can answer that - but first I have to buy one.
There is one thing: I always let my shaft spin when I am sailing so I guess I wont's see that much difference under sails (maybe in light winds).
What I can summarise is that folding props give you more power when going ahead, slightly less when going astern and some extra zero point smth knots when sailing. And when sailing - you are not picking up every net, rope or a plastic bag swimming in the sea...
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Post by Don Reaves on Apr 7, 2019 13:07:38 GMT
I’m not sure why it took me so long to get around to reading this article. It’s very informative. It also confirms my experience with the Kiwiprop on my SO35. Slightly less forward speed but better backing power than my previous 2-blade prop. However, I find it very interesting that they failed to understand how the Kiwiprop works. I have to use two hands to demonstrate the action, one to hold the shaft, and the other to turn the hub. The blades then rotate backwards so the same leading edge is used in reverse.
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Post by rene460 on Apr 7, 2019 22:50:44 GMT
Hi Ales,
I am not sure that I quite understand your summary.
With a folding prop, the shaft normally does not spin when you are sailing, whether or not it is in neutral. The difference in sailing performance between the fixed propellor is due to the difference in drag when the boat is towing it through the water. The fixed prop, like towing a bucket, but the folding one changes to a nice streamlined shape when you are sailing.
Forward and reverse performance is about motoring. When motoring, the boat speed depends on the thrust from the propellor at the rpm it is turning, and also to the speed the hull moves through the water in response to that thrust. I suggest the differences in performance motoring is more about how well the actual pitch and diameter convert engine power into thrust, while the differences between brands is also affected by details of blade area, blade shape and so on.
Feathering propellors often have the facility to adjust the pitch after installation. (Easier to do out of the water than by diving). If you are really keen to extract that last bit of motoring performance, you can adjust the pitch a little for more thrust of for lower engine load, so higher rpm, even if only one opportunity for adjustment per year. Some of the variations in that YW report suggest that there might be more in just how closely the supplied propellors match the actual test boat and motor. The Gorilla being an obvious example where they may have tested the wron propellor selection.
Hi Don, I tend to agree that there are areas in the report that could be improved, but it is still the best effort I have seen. They did a huge amount in only two days, a pity that they could not have spent just a little more time to do it better. Then, as usual, the editor has had his/her way with it, and left out information that would have been interesting to readers. They thanked the supplier of underwater camera equipment that they used to check operation of the props in the water, but there was no mention of what they saw in the write up. Always the same when the accountants design the test programme.
rene460
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Post by hoppy on Apr 8, 2019 1:53:22 GMT
I've never understood the fascination of reverse performance of props. For cruisers 99.99999% of your motoring is done forwards so it seems totally logical to chose a folding/feathering propeller that improves your forward speed and gives you better fuel economy. If there are two props with a similar forward performance, sure then think about which is better in reverse.
Having to give it a few extra revs in reverse and learn that you need to start the reversing a little sooner to stop really is no big deal. Maybe stopping power is a little more useful for charter boats with ham fisted crew on board.
As for the prop walk, I love it and would hate to lose it...
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Post by zaphod on Apr 8, 2019 6:32:10 GMT
Thank you rene460 for your comprehensive answer. I've read (probably) all the post regarding folding props and also that YM test. I am aware that it is a tough question what will a folding prop bring you and only I can answer that - but first I have to buy one. There is one thing: I always let my shaft spin when I am sailing so I guess I wont's see that much difference under sails (maybe in light winds). What I can summarise is that folding props give you more power when going ahead, slightly less when going astern and some extra zero point smth knots when sailing. And when sailing - you are not picking up every net, rope or a plastic bag swimming in the sea... Even if you let your fixed prop spin it is still creating significant drag, and many transmissions don't like it. Not only that, the spinning prop is also creating quite a bit of turbulence which does affect the efficiency of your rudder. You will likely see a noticeable performance difference with a low drag prop even if you let your fixed prop freewheel.
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Post by rene460 on Apr 8, 2019 10:48:07 GMT
Hi Hoppy, I am with you on that. I use reverse to stop in the pen, and to stop within my wife’s reach of a post to drop the centre line over when arriving at a jetty. In both circumstances, I need to be able to rely on reverse, but would never select reverse while still going 6 knots, but it would be difficult to accurately repeat tests of stopping distance from minimum steerage speed to make an interesting test. And if reverse is your only criterion, a good fixed prop will always be satisfactory. I would use reverse for no more than half a boat length each time I pull up. It’s nice to not need excessive rpm, and be able to stop with minimal fuss.
Likewise, going forward, while the maximum speed reached is an indication of the maximum thrust produced, but realistically this is rarely required. Not to say that you would not be glad of it if circumstances meant you needed it. But for normal cruising, it is obvious from many threads that none of us like to go far at maximum rpm, and if you are doing 80% rated rpm, there is only a few rpm between different propellors to achieve a similar speed.
There may be a difference in the tendency to pick up floating ropes etc between a spinning fixed prop and a feathered one, and I would expect the folder to be good in this respect, but I have no knowledge or experience in that area. The next biggest concern is reliability, and it is hard to beat a fixed prop there. Prop walk is certainly something you either love or hate. Useful when you learn to harness it, and you get used to it’s absence if you don’t have it. But any change in propwalk when you change propellors would be disconcerting.
So the main reason for changing to a folding or feathering prop is reduced drag when sailing. Even round the globe races are often won or lost by a very small margin, and cruisers also have plenty of reason to reduce drag and sail a bit faster. To reduce drag without sacrificing reverse thrust for stopping in the pen was certainly my reason for changing.
rene460
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Post by hoppy on Apr 8, 2019 11:14:01 GMT
cruisers also have plenty of reason to reduce drag and sail a bit faster. If you get an average gain of an extra 0.5 knot speed from a folding/feathering prop, that's an extra 12 nm per day. On a daylight passage, that's a 1 hour earlier arrival and on an Atlantic crossing of 20 days, that puts you 240 nm ahead or a 1.5 day faster crossing.
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Post by ales on Apr 8, 2019 17:31:16 GMT
Thank you all for your opinions.. hoppyActually I do most of my motoring in reverse. There is nothing more beautiful than to lay down in the cockpit facing stern, drinking a glass of wine and having a nice view cruising 6 kts ... in reverse. Just amazing...
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Post by MalcolmP on Apr 8, 2019 21:05:16 GMT
Thank you all for your opinions.. hoppyActually I do most of my motoring in reverse. There is nothing more beautiful than to lay down in the cockpit facing stern, drinking a glass of wine and having a nice view cruising 6 kts ... in reverse. Just amazing... 😂😎😂😎👍
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Post by hoppy on Apr 9, 2019 12:34:57 GMT
Hahahaha
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Post by ales on Apr 9, 2019 12:55:29 GMT
had to do it hope you don't mind:) (guess not)
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