The benefits of a lower mass Propeller

The KiwiProp is often 1/2 the mass of the competition.  It’s easy to see why with all of the elabourate bronze or Stainless pieces that make up most feathering propellers.  Our simple Stainless Steel Hub with composite Zytel blades comes in at less than 3.4kg.

Intuitively it must be easier for your engine to get 3.4 kg spinning than say double that for most of our competitors, but that advantage is shortlived.  When you start talking balance and vibration throughout a drive train, many boat owners have dealt with vibration issues at certain rpms, no real explanation other than you’ve got a slender mostly unsupported shaft trying to spin a large diameter propeller.

The potential for vibration is directly proportional to the amount of mass you are spinning AND it’s distance from the centerline of the shaft.  Whether or not there are any wear issues over time or impact related variations, the potential is there simply because the mass is there (or maybe not there in the case of a broken blade).  A quick look at the KiwiProp and you will notice that likely 90% or more of the mass is concentrated in the Stainless Steel hub close to the shaft.  This hub is so strong that we have never seen one damaged or bent, even in cases where the blades have been totally destroyed (that’s a story for a boat show if you ever cross paths with us!).  In sharp contrast every bronze and full stainless steel propeller on the market relies on a significant amount of mass in the blades in order to initiate their feathering or reverse engagement.

Visualize the momentum of a heavy tip weighted bronze blade slamming into position repeatedly versus our lightweight Zytel blade simply flipping over onto its pitch stop thousands of times throughout the life of your propeller and its easy to accept that there is likely a benefit to spinning 3.4kg around rather than 7-9kg of elabourate finely machined bronze.  There will never be any data to demonstrate how this might make your drive train happier in the long run, but anecdotally we can tell you that we almost never have any vibration issues, and the other guys almost always do- eventually.

I can’t count how many times a customer has hauled their boat and found a piece of a blade missing, remembered hitting something earlier in the season but thought everything was fine because there was no vibration or performance change.  Everything was fine, small chip, fix it with epoxy and filler, big structural chunk missing you might want to order a new blade for $110 that you can replace yourself in under 5 minutes.

Fair Winds

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KiwiProp Pricing

This Blog was not intended to sell KiwiProps per say, but if you just wandered onto the site and don’t know much about our props, the K3 three bladed prop that has been around for over 15 years is $1500US including express post to your door. It will cover most boats with a 10-60hp engine. The K4 covers the range from 55-100_ hp for $2850. Transmission ratios, boat size and shaft dia dictate the cutoff point for both. We know we are much lower priced than any other feathering 3 or 4 blade props on the market. That is a direct result of our KISS design principals, and also employing common components across the range and taking advantage of new materials for construction.
You may have heard the rumors that we’ve been dabbling with a 2 blade folding all composite propeller, and the KiwiProp SD specifically for saildrives. Both rumors are true, and prototypes of both are out there being tested.

KiwiProps- What Wears Out?

Nothing lasts forever right?

KiwiProps have proven to be extremely durable, and more importantly reliable. We can honestly say that if you keep a new Kiwiprop properly lubricated there are no components that regularly wear out or require replacement.

We have learned a few things over the years, however, that have led to design and material improvements often because something has ‘worn’. There are two items that led to material changes about 5 -7 years ago.

The White plastic nose cones on the aft end of the KiwiProp for some reason started developing cracks after 5-7 years in the water. To date likely less than 5% have been susceptible, but we’re no closer to understanding why. Likely some combination of fatique, impact and loads due to lack of lubrication, but no matter, the fix was to go to a slightly softer black material and we have had no issues since.

We supply the replacements n/c if your white one has a crack appear, but worth noting that even if it cracks it does not indicate imminent failure. As a matter of fact we have only had one case where the nose cone actually became partially detached and it was related to an impact situation. We often tell customers that we’re happy to send a new nose cone, but if it’s just a small crack just keep an eye on it, it may very well never get any worse or impact the performance of the prop.

The other item seems to be blade mounting pins. Again not a big issue but in the real world of marinas and boat clubs, it became apparent that when there was stray current, the pins, mostly hidden within the blade, were the most susceptible part of the prop to corrosion, resulting in the loss of a handful of $100 blades over the years.

They also seemed to show some wear when a KiwiProp was run without proper lubrication for a long period of time, again hidden for the most part.

The solution, about 5-6 years ago was to go to titanium pins and again we have provided them n/c as replacements for lost or worn pins. I still have a hard time visualizing how the SS pins were wearing, but its hard to understand all the forces acting on a propeller when powering ahead and in reverse, and also when feathering.
Many customers (and competitors) have questioned whether or not the Zytel blades wear out. The short answer is no. The real world answer is that they are a low cost sacrificial replaceable part though so in the event of collision, lobster pot wraps, dinghy painters, etc. they can be easily repaired with epoxy and filler in the case of minor dings, or replaced entirely for $110/blade.
A number of blades have been scored at the base due to a lack of lubrication or over pitching of the pitch screws but it might be unfair to call this wearing out as both conditions are self inflicted by the owner. The blades are normally OK if there is minor scoring, the eventual symptom will be to overpitch in reverse which since we are already at maximum pitch you might not even notice.
It has initiated a redesign of the reverse rollers to increase the surface contact area and spread any load that might want to ‘score’ the blade, we ship out replacement rollers n/c for anyone that is concerned about the scoring and will advise on whether the amount of scoring looks like it might warrant further repair (epoxy and filler or worst case new blade).
Well there you have it, a long winded overview based on selling and using the props for 13 years! Fair Winds.
BTW- my 13 year old KiwiProps still have their original nose cones and pins so go figure!