Jump to content

Opinions on folding/feathering propeller


Recommended Posts

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.

Link to post
Share on other sites

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.

Link to post
Share on other sites

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/

Link to post
Share on other sites

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.

Link to post
Share on other sites

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 ;-)

Link to post
Share on other sites

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.

Link to post
Share on other sites

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.

Link to post
Share on other sites

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. 

Link to post
Share on other sites

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.

Link to post
Share on other sites

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.

Link to post
Share on other sites

I believe kiwi props are now saying not to use on less than 30hp because of the reverse issue,can stall small motors,16hp yanmar when going in to reverse had to put in reverse then give power quickly otherwise it stalled,but once in reverse could idle backwards.

Link to post
Share on other sites

Autostream is adjustable in forward and reverse so this issue should never happen.  TBH I'm a little confused as to why the Kiwiprop would stall out any engine when going into reverse - surely the pitch is different in reverse to allow for the different gear ratio in reverse?  Or is it something to do with bangin' it into reverse at 6 knots?

Link to post
Share on other sites

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) not as great as I remembered.

Shadowfax in the air.jpg

It looks like a feathering two blade on the picture...  maybe a reason for it. 

Conclusion: due the engine size and the nature of Kiwiprop that is out, let see the available space and go from there. The preference is geared folding type (two or three blade)... but who knows

Thanks for the comments anyway

 

  • Upvote 1
Link to post
Share on other sites

I’m doing this this week

Currently have 4 blade Volvo on 52ft 18t Yacht 110hp shaft

It now done over 4K hours and blades rattle and shaft rotates at anything over 7kts under sail

So we have had our value out of it

 

I’ve been told multiple times to stay away from Gori

Considered Max but am going Brunton Varifold 3 blade

 

 

As for the OP I’d be going Briski two blade geared folder

Link to post
Share on other sites

We have a max prop 3 blade feathering on a 15 ton 50fter with a 110hp motor. No issues at all in 15,000nm so far and performance seems to be very good under sail and motor-never been passed on either.

I do make a point of servicing it whenever we come out of the water.

  • Like 1
Link to post
Share on other sites

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/gear/folding-and-feathering-propeller-test-29807

http://www.flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf

 

One is a web based version, the other a pdf version. Both essentially the same, same photos etc, just some slight formating.

The pdf version states the propeller size and pitch for each prop trialed. The sizes are not the same. It appears the target is 16 x 11, but the diameter ranges from 15 to 17, and the pitch ranges from 11 to 13. That would be fine, accept the test reports various measures of power, speed and efficiency. Its the first rule of propellers that the bigger diameter the more efficient, and the greater pitch the faster the boat should be able to go for any given rpm. The test ranks the propellers on all these various measures of power and efficiency, but it all needs to be taken with a grain of salt when the sizes are varying.

 

The other big propeller assessment was done by the French magazine Voile. Kiwiprop refer to this (as this assessment makes the kiwiprop look like a better performer):

http://www.kiwiprops.co.nz/cms/index.php/k3-resources/voile-analysis

The guts of this assessment is boat speed at various engine rpm. This test notes that there are a number of 'faster' props than the kiwi for set rpm, BUT that all but one of those faster ones can't reach maximum rpm, i.e. the engine is overloaded and any engine warrantees would be voided.

 

Neither of these two magazine prop tests mention how much time was spent matching the prop to the boat, gearbox and engine, which is a major task, On the Yachting Monthly one, it appears Gori had a dummy spit, cause at the end of the pdf article is a box stating Gori reckoned they sized their prop wrong and want another go at a different size, thus making it appear better performing... In the Voile analysis gori also used two sizes, this makes it appear Gori simply can't predict the size for any given installation. Go drop $5,000 to see if Gori's size guess actually suits your boat.

 

Anyway, there is such a bewildering array of metrics in these tests to express how good each prop is. In reality, they all make the boat go forward. What no one mentions is how long they will last, how complicated the maintenance is, how expensive the maintenance is, and how hard they are to match to your gearbox / engine set up.

 

Whether feathering or folding, any moving parts in the marine environment, especially metal on metal, are going to suffer wear. Some comments hear from people who actually use props are about them flogging out, getting their money's worth of the hours, complexity of actually using the prop (going in reverse, shagging gearboxes, grease requirements etc).

 

I've seen some work of art shiny metal props at boat shows. I've seen some flogged out hubs and warn mesh teeth on the hard stand. I've heard of summer holidays to the Barrier get disrupted by pins dropping out and blades going for a swim.

 

I'm thinking the media (magazines) are focussing too much on the finer points of performance, where, due to the difference in installations, prop sizes etc, you can't honestly assess different props to such a degree of stated accuracy for power and efficiency. The real issues are cost, complexity and expected trouble free operating life. 

  • Upvote 2
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...