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Opinions on folding/feathering propeller


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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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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?

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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

 

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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

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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/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. 

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