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Opinions on folding/feathering propeller


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I had a great reading about autopilots after I asked for opinions and that was a great help to make my decision, so here is another theoretical question, well not so theoretical as I'm looking to replace my existing three blade fixed propeller and it seems a good idea to go for something more sophisticated (complicated). Earlier I researched about these propellers and I realised all manufacturer makes better product than the opposition.

Anyway I kept Kiwiprop and Gori on my shortlist, and honestly I tending to go for the Gori, just because it looks more robust for me.

I really would like to hear opinions, experiences with these, or even about other brands.

Just to be precise with details, the boat is 33', 2GM20 engine with a 2:1 gearbox and about 5t displacement when ready to go.

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There is some real devil in the detail with propellers. Referring to the yachting monthly test that Farrari referred to, I see there are two versions on the internet: https://www.yachtingmonthly.com

Kiwiprops reverse pitch is not adjustable. There is too much reverse pitch, and therefore torque required to rotate, for some small engines to overcome at idle...

Lots of great info, I learned again. Actually I have to check the clearance between the shaft end and the rudder. In memory I have plenty of space, but looking this picture (one of the 15 Chargers) no

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We've got a kiwiprop and are very happy with it. The big advantage of the kiwiprop (and anything else that you can do this with) is to be able to simply change the pitch of the blades. Means you don't have to spend lots of $$$$ and stress about guessing you've got the prop size just right at purchase.

 

Kiwiprops do need periodical service, i.e. every five odd years some parts may need replacing. It is very easy to change the blades. They promote this as a feature - if you hit something in the water the blade will break first, rather than bend or ding an expensive bronze one, or stuff your shaft, P bracket etc. You can even change them in the water if you are good at holding your breath $110 ea +GST. If you are going offshore take a spare set with you sort of thing. I understand there is a notable cost difference between a gori and a kiwi.

 

Handling characteristics - kiwi are solid in reverse - no problem there, as for forward thrust, you can adjust the pitch till the cows come home, i.e. perfectly match speed for max revs, increase cruise speed at the expense of max revs etc.

 

One thing you will find, with any feathering / folding prop, your sailing will improve substantially. Not just speed on all points of sail, but your ability to point will go up substantially, possibly as much as 10 degrees higher. You will wonder why you towed a dinner plate around for all those years after going to a feathering / folding.

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I went through this years ago for my 44' cruising boat.  Ended up with an Autostream stainless steel 3 blade feathering.  I'm very happy with it.  Pitch is adjustable in the water.  Stops the boat in reverse like a dream.  It was half the price of a Maxprop and cheaper than a Gori.  My engine is too big for a Kiwiprop.  One thing I have heard regarding the Gori "Overdrive" facility is that it shags your gearbox, which don't like going forward/reverse/forward at cruising revs.  Haven't witnessed it myself but it was from a reliable source.  Autostream is made in Melbourne.

 

http://www.seahawk.com.au/

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Yeah I have heard nothing but good on autostream, Bought the right one for engine and revs but it clashed with my rudder when featherd so had to sell and get a Kiwi.

Someone told me, I forget who, that Kiwi's go out of feather mode when you go fast? Like >10knts.

That would be a piss off. 

OK, i hear the murmur.... i don't often go >10, but it does happen surfing from time to time.

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Someone told me, I forget who, that Kiwi's go out of feather mode when you go fast? Like >10knts.

That would be a piss off. 

OK, i hear the murmur.... i don't often go >10, but it does happen surfing from time to time.

They're designed like that, they are foils y'know, if they didn't go out of feather above 10 knts, the back of your boat would start lifting out of the water like TNZ, but since you don't have a kiwiprop forward of the keel you'll just go bow down and do a handstand.

 

PS, I've gone 17 knts down a hill with ours, no problems from the kiwiprop, keeping the boat under the rig when we hit the bottom of the hill was demanding more of my attention at the time ;-)

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I replaced my Kiwiprop with a 2 blade Flexofold.  I like the Flexofold as it has slightly less drag and isn't so hard on the gearbox in reverse; I also get a little more speed in forward gear although I may have also been able to achieve the same with the Kiwiprop if I had adjusted it.  The yachtingmonthly article was a useful reference for me.

 

https://flexofold.com/folding-propellers/7-saildrive-propellers/

 

https://www.yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807

 

I still have my old Kiwiprop if anyone is interested in it.  It will need new blades however.

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I was dead keen to get a Gori when I repropped my Volvo D18 on a 5t yacht, they are a work engineering beauty to lust over.

Problem was I didn't want to change the 1" shaft and they were super heavy compared to the Bri-ski geared folding prop. Gave me concerns about the load on the shaft bearings/balancing so ended up with the Briski and the sideways walk that goes with it , but I'm a yacht and prefer the sails anyway.

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My 2 cents worth; Kiwiprops are quite popular with cruisers because they very cheap compared to the opposition and offer some benefits re pitch etc mentioned above and awesome reverse. However they have a few problems, the first is that they need a lot more regular maintenance than a bronze or stainless folder/feathering prop and the second which is common to all feathering props is that they are not that efficient hydrodynamically. If you have a look an efficient prop it will have a foil designed to create maximum lift for the expected operating conditions, usually it will have a thin section and twist in the blade to account for the higher tip speed. The kiwi has no twist and has  an inefficient foil due to the way the blade is mounted to the hub on very fat stubs.  The first issue is a matter of diligence, the second you cannot get around but is not really a major concern unless you are short on power. Independent prop tests bear this out, you will burn more diesel getting from A to B. For racing they are not also that good despite the insistence of people that they have the same drag as a folder. Before and after testing bears this out.

 

Unless you really want a feathering prop, I would go for a two bladed geared folder on a small to medium yacht, and if doing a lot of motoring or have excess grunt on tap then perhaps a three bladed geared work of art like the Gori or a feathering three blade. 

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Autostream is very good - ours is on 60hp with 3 blades - feathering stainless.

Has done about 2000 hours over 12 years and no maintenance apart from zinc change and occasional shot of grease and coating with propspeed. Easily adjusted for pitch and excellent performance forward and reverse. Cruise 7 knots max 8 knots on 40 footer. 30mm shaft.

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Well, Island Time is about 8 ton loaded for offshore, 12m long. 43 hp Volvo. I’ve had a kiwi prop for most of the last 30000 nm. I’ve also got (in the shed), one of those fancy curved blade Volvo folders.

I like the kiwi prop. It’s cheap, easy to remove to change the saildrive anode (120s saildrive, circular anode, not split like the newer ones), as it comes off in one piece.

I’ve not had many issues with the kiwiprop, once I sorted that you must grease all the grease points, and make sure the reversing rollers are free, every time the boat is slipped for any reason.

If the kiwi prop is perfectly pitched, it will out perform the Volvo prop, but that is probably because the Volvo prop seems to be out a bit - perfect for IT is probably between two standard pitches.

Reverse being full pitch can be an issue for small engines with a kiwi prop, as they can stall on gear selection. Anything over say 30 hp should be fine.

I’d have another kiwi prop any time.

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