Flex-O-Fold Propellers vs Kiwi

[Sail Warehouse]

Agree with what Bash said. I have 2 Flex o Folds (twin Volvos). Good performance and very high quality but proprietary zincs are a bit of a pain. FoF is good about shipping Zincs quickly so it has not been a problem though.

[Moby Dick]

2 x Kiwi props fitte on twin Volvos, one full year of use, no problems.

Real grip in reverse, took some getting used to - more than fixed two blade - but very useful. Speed gain under sail, or when motor sailing using one engine. A lot more extra grip in forward compared to 2 blade fixed.

MD

[jbinbi]

Going on 3d season with kiwi prop. So far, so good. Have re pitched last year by just turning set screw, will do it again this year to get a bit more top speed. Put on very little anti fouling year one, and had barnicle growth when hauled in Oct, last year put on more anti fouling, had less barnicle growth, but some. Did not have boat scrubbed or cleaned at all last year, so this was very impressive. Easy to maintain, just add some grease. No need for zincs, as blade and root are plastic, but will hang a fish this year. I lusted after some of the other feathing props that are costing $3500, but my wallet won out in the end and at $1100, I have been really happy so far vs. keeping my fixed 3 blade.

[Jim Cate]

Originally Posted by Sail Warehouse

Agree with what Bash said. I have 2 Flex o Folds (twin Volvos). Good performance and very high quality but proprietary zincs are a bit of a pain. FoF is good about shipping Zincs quickly so it has not been a problem though.

G'Day, SW,

FWIW, I've had a f-o-f 3 bladed prop on I-2 for 5 years now, and had the same gripe about the proprietary and expensive and apparently water soluble sincs. So, a few years ago, I started making my own! Used a "button" zinc such as are often used on rudders for material. Requires using the cover plate that goes over the gears as a template and then drilling three spots out for clearance on the socket-head screws that secure the cover. No great precision needed, and it's easy even with a hand held drill motor. Saves a heap of money, too!

And for the original poster, it seems odd to be comparing the Kiwi prop and the flex-o-fold, since they are quite different beasts: one is feathering, the other folding, and their performance characteristics are inherently very different. We've been very happy with our f-o-f for 5+ years now. No problems whatsoever in some 1500 hours of use.

I believe that you will find that the folders are more efficient than feathering props, due to the non-twisted blades that are a part of the feathering design. The lack of twist in the blade's shape results in less efficient coupling of the engine's power to the water, and this in turn is reflected in reduced fuel economy if nothing else.
The enhanced thrust in reverse from the feathering prop may or may not be important to you... depends on your application and driving style!

The ability to fine tune the pitch is a nice feature, and one that is incorporated in most feathering prop designs today. Most allow adjustment of both forward and reverse pitches. You might look at the Australian Auto-Stream design before you decide on the Kiwi prop if you really want a feathering prop.

Enough ranting! Good luck with your choice

Cheers,
Jim and Ann s/v Insatiable II

[Sail Warehouse]

Jim, that's a good idea. I think I'll try making a template and do my own zincs. Thanks for the idea.

Jim (also)

[markpj23]

Hey guys you don't have to roll your own any longer. Although it may still be cheaper to do so...

Flex-O-Fold prop zincs are now available on BoatZincs.com Flex-O-Fold Propeller Zinc Anodes. (I have no affiliation with them at all, just a customer.)

[Sail Warehouse]

Another good tip. Thanks Mark. They are a little less $ than buying from FOF too.

Jim

[lampe]

Hi to all,
we just bought a Flex-o-fold propeller because we are confident of the quality.
We know many that have a Flex-o-fold in this area and all of them are very
satisfied.
Keep you updated as soon as boat is in the water.

[Bash]

I just ordered 6 six zincs to get the free shipping, and ended up paying as much for them as I normally pay for two plus shipping.

This ought to keep me set for a few years.

[witzgall]

We currently have a fixed two blade prop. What performance under sail and power do you think we would find if we went to the Kiwi?

Chris

[Esprit Marine]

The only advantage of a feathering propeller over a folding propeller is the bollard pull astern, which allows better maneuverability when reversing.

Otherwise the bollard pull forward is lower than with a folding twisted propeller, and the efficiency at cruising speed is also lower so more fuel consumed for the same speed. The Kiwi prop profile is particularly thick, so efficiency should be poor.

From this test report, the FOF has the best efficiency after the Autoprop. Pity though that three propeller manufacturers had selected an incorrect pitch, and the test has not been redone with the pitch corrected.

[Marinheiro]

Interesting report from Espirit, but not sure how you concluded FOF was the most efficient following Autoprop - have a look at the numbers for Varifold (makes me happy this was the one I bought).
Also interesting that the reputation for greater astern thrust for the feathering props (esp Max) does not appear to be demonstrated, the Varifold was better than Max and only just behind the Variprofile.
What I would like to see is a test for 50-70 hp motors where 3 blade props would be compared.

[Esprit Marine]

Marinheiro,

Putting aside the four propellers with incorrect pitch, on the simulated Bavaria 34 with Volvo D1-20, the Autoprop has an oustanding propeller exponent of 3.2, FOF and Gori 2.5, fixed two blades and Varifold 2.3, and Maxprop 2.1.

Considering the pitch is correcty selected for a max load at 7.6 knots and 3200 rpm, at the cruising speed of 6.4 knots, the yacht with Autoprop will consume 2.7 l/h, FOF and Gori 3.1 l/h, fixed and Varifold 3.2 l/h, and Maxprop 3.3 l/h.

The static thrust for the four tested folding 2-blade propellers is in average 45% higher than for the three feathering propellers forward, and 15% lower astern.

[feelsgood]

I sailed a 34 sadler that had a maxi prop that was coated with coppercoat antifouling . It sailed so much better than with the fixed 3 blader and never got weed on it. It worked well in ahead and astern. As has been said if you are looking for sailing erformance then I recommend the maxi prop

[Marinheiro]

Esprit, you are obviously making some additional calculations, but as usual in most propellor tests the baseline data is not truly comparable because most of the propellors are not sized correctly for the engine.
Auto prop gave great performance, but as has been seen in tests before will not let the engine reach maximum revs. It is apparent that both the FOF and Gori with 12" pitch (c.f Varifold with 9") are too coarse for the installation - of course these will give slightly better figures at lower revs but I am not sure about your fuel consumption calcs - there will be a greater loading on the props so consumption would expect to be higher for a given engine speed.
When a set of test data is produced where each prop being compared allows the engine to attain max revs and at the same time achieves max rated fuel consumption then some real conclusions can be drawn. I think this would take a lot of experimentation.
The Hallberg Rassy web site has some interesting motoring performance data for their yachts, particularly highlighting how expensive the last knot in speed is fuel wise
Disappointing the Kiwi prop was not included in the test -would have been interesting to see how it performed.
The Kiwi prop was originally developed to replace the old style non-geared folding propellor at a similar price range. I do not think it was considered to compete with the much more expensive all metallic feathering props and geared folders. Of course its thick flat blades will not be as efficient but it has been a leap ahead compared to what it was replacing and has a very good reputation in NZ