Rollers……….

Much like grease is the most commonly overlooked maintenance item, Reverse Rollers tend to come up as really the only replacement part we send out with any regularity. Most of that activity is related to older props that still have the older smaller diameter bolts that were prone to bending and/or shearing off due to impact. After we upgraded to larger diameter bolts about 10 years ago the problems more or less went away but we have continued to improve the design for another reason.
A lack of grease in the hub for prolonged periods often results in ‘scoring’ of the blade roots where the roller contacts the blade in reverse and subsequently stays in that position due to the lack of lubrication. The blades can often be repaired, and no harm done to the rollers, but we did decide to change the profile of the rollers so as to increase the surface area of the contact, thereby reducing the point load that was causing this scoring.
The end result is the tri-lobe rollers that spread the load across a larger area and for good measure we added grease caps onto them and the grease helps keep any debris and precipitate off the bearing surfaces.
It’s important to note that the rollers don’t spin or anything, they merely rotate a 1/3 of a turn or so when reverse is engaged and hold the blade in the reverse position. Most people never grease the old ones, but it can’t hurt and if it keeps mineral deposits out of there so much the better.
Worth also noting that your annual inspection should include a quick look at the rollers to make sure the bolts are tight and that they are rotating freely. If you have any issues contact us as they are easily upgraded to the latest version.

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New Blade Design now Standard

After several years of testing and modifying Kiwiprops has finally standardized on a new and improved blade design. Visually you have to look very close to see the differences but if you compare it to the first blades over a decade ago, you can see a number of refinements over the years that have lead to these stiffer, stronger, more hydrodynamically refined blades. The trailing edge is where you will notice a minor change, where a slight ‘wedge’ shape has been incorporated to improve motoring efficiency. Of course all of this was done with an eye towards maintaining the naturally low drag approach of symmetrical blades.
These new blade shapes have been incorporated in all new props shipped, and, of course, they are backwards compatible with previous props. We’re not quite to the point where we would recommend switching to new blades as there really was/is nothing wrong with the older ones. Just nice to know future replacements due to damage should perform better than the originals. Fair Winds.

Service Calls in Georgetown

Enough with the technical posts.  Every once in awhile I’m reminded that even though it seems like we’re just selling propellers, our products do have an impact on people’s enjoyment of their cruising ambitions.  Recently I got a call from Mike Hassell, a Lagoon 440 owner.  Now Mike would tell you he’s a bit of a neophyte when it comes to boats, cruising and technical things, but he’s blessed with an ability to jump right into problems and figure them out.  I can’t even remember the full story, but Mike inherited his KiwiProps but we helped him get them setup correctly about 2 years ago with a new set of our larger 19.5 blades and a minor tuneup.

Anyways, Mike calls me and tells me he loves the props but that he’s been messing with the pitch so much- just because, that he’s now got a minor vibration issue that needs sorting out.  I walked him through the procedure over the phone, then asked him where he was dropping his hook since we last talked and he said they had just arrived in Georgetown in the Bahamas.  Well as it turns out I was flying down there in a few days to hang out with my good friend Bernard who also happens to do most of the shop work for me on KiwiProps and a lot of the beta testing and experimental design evaluation.  I told Mike to stick his head out of the cockpit and see if there was a 46′ cat nearby called Ti Matou, sure enough Bernard was a couple boats over.  I told him to throw the prop in the dinghy, OK maybe a bottle of rum might be a good idea too, and make his way over to Ti Matou and Bernard would get him sorted out.

By the time my wife and I arrived, Mike couldn’t believe his good fortune and had a Georgetown welcome pack waiting for me, that would be a case of Heineken and a bottle of rum, and of course, on board instruction on how to use both.  We enjoyed several nice evenings, going over he and his wife’s travels, and after several rums decided we needed to tweak the props some more, sea trials followed, etc. etc. and after a few days they sailed over the horizon spreading the good word about KiwiProps.  Thanks for the fond memories Mike, and to Bernard and Claude for the hospitality on Ti Matou.  Fair winds to any of our cruising customers out there doin it!  Reminds me of why I sit here in front of my computer helping out!

Jamie

Chasing Motoring Speed w Pitch

We have stated previously that Propeller design is very much an optimization process. There is lots of empirical theory on how best to increase speed, decrease drag, improve reverse, decrease cost, decrease complexity, etc. the real trick is balancing all of the factors so that it appeals to the largest segment of the sailing population.

We thought that a published example might be illustrative so that the informed buyer could realize how simple it is to ‘play’ with test results.

Voile Magazine performed one of the more comprehensive comparative tests using a Jeanneau Sun Odyssey test bed and a good cross section of the propellers available at the time (2009). There have not been a lot of epiphanies in propeller or design theory since, so it remains one of the best collections of real world data.

http://www.bomarine.net/index.php/download-document/65-test-voiles-magazine-autoprop-april-2009.html

It is normal to have your eyes drawn to the speed at 2200 rpm line of the chart as a good measure of what your real world experience might be with each prop. What will my vessel speed be at a reasonable cruising rpm? If you poke at the data a bit, however, you will realize that this line is almost meaningless.

One of the most important services that we provide as the sales agent for KiwiProps is matching our propeller range with your vessel and powertrain. The objective is to setup a propeller with a load curve that is matched to your engines power curve so that the engine can reach its maximum rpm and no further. This is critical to the long term life of your engine, and improper loading will actually void most manufacturers warranties.

So go back to the chart and look at the line above the 2200 rpm speeds and take a look at the max rpm ratings. THESE SHOULD ALL BE 3600 RPM. Not one is over 3600, and 4 of them highlighted in red are significantly under. Every manufacturer knows this should be 3600 and they supplied the preconfigured propeller SO WHAT IS GOING ON HERE? Since propellers out of the box are a ‘best guess’ your fixed propeller remains a best guess for the rest of its life, but virtually all feathering and folding propellers offer the option of fine tuning the pitch to match up the max rpm. SO WHY WAS THAT NOT DONE?

The simple answer is that several of the manufacturers realized this was primarily a speed test so they supplied overpitched props to produce higher speeds at lower rpm. The fact that this would ultimately overload your engine for its entire cruising life was not factored in nor highlighted. I graphed the data Vessel speed vs inverse max rpm and this approach is clearly visible in the KiwiProps commentary on the website:

http://www.kiwiprops.co.nz/cms/index.php/k3-resources/voile-magazine-2009

Scroll about halfway down to the Cruise Speed vs Max RPM graph and you will see that far from measuring motoring efficiency differences between props we are actually measuring differences between pitch/dia or load settings.  We have superimposed a best fit line onto the XY plot.  To put this in perspective, it is entirely possible that we could provide 10 different KiwiProps and produce the same range of results.

To be fair, there is definitely something to be learned with regards to overall efficiency, fuel consumption, vessel speed @ rpm and KiwiProps, as mentioned in a previous post, is actively working on modifications to our blade designs to chase some of these efficiencies. Really interesting stuff, but unfortunately the Voile article doesn’t go into enough depth. Contact us if you’d like to know more!!!

Free Spare Blade at the Boat Shows

About 10 years ago when we did our first boat show, we decided we needed to come up with something as a ‘Boat Show Special’.  We came up with the idea of a free spare blade which is worth Approx $110.  The problem with the idea was we have now managed to create the impression that you ‘need’ a spare blade 😉  Of course a couple of our competitors may have furthered that thought process in their sales pitches.

Reality is we sell very few replacement blades, except in situations where the customer has hit something and totally destroyed one or more often all of them.  The zytel blades are actually stiffer and more durable than a bronze blade and will take quite a beating.  The point was supposed to be that IF you damage one, they are easy to replace yourself vs throwing your bronze propeller away or trying to get it rebuilt.  The other selling point was the low mass of the blades being able to tolerate minor damage and still function because the propeller is not thrown out of balance.

So, after much discussion, we decided we have to come up with something else before the next boat show!  If you filled out a form at Annapolis, take advantage of the free blade now as it likely won’t get repeated!

Low Maintenance vs Maintenance Free

I could have called this post Grease, Grease and more Grease!

There really is only one critical maintenance task on your KiwiProp, and that is keeping it greased.  More specifically, keeping the hub greased.  The darn thing is in a hostile environment, and while the moving parts don’t actually move that much, they do need to move once in awhile, and annual greasing is hopefully not too much to add to your boat maintenance routine.

I always say the best prop is the one you put on and forget about because it just works, well if you totally forget to grease your kiwiprop for a few seasons it will stop working, or will at least stop working properly.

If you do a quick google search on KiwiProp Reversing Issues, you will find a number of old comments (I couldn’t find any recent ones maybe because our message is getting out there) regarding reverse issues.  When I go through them well over 95% of the problems are related to a simple lack of grease over an extended period of time and then guess what, other issues start to manifest themselves that don’t seem related to the customer, but they are.  Since we sell direct, we don’t have a network of dealers out there making sure the lubrication message is reinforced.  It is a simple one though  GREASE YOUR KIWIPROP ANNUALLY, it only takes 5-10 minutes and can be done underwater.

OK, what about the other 5%?  Well it can be challenging to decipher a customers interpretation in a post, but the only other commonality is impact or fouling damage to reverse rollers on older units that have either sheared them off or bent them and caused them to work their way loose.  With thousands of props out on the water for over 15 years, its important to keep these issues in perspective.  If I was guessing I would say that 5-10% of our customers have a lubrication issue at some point, 90% of those fix it by greasing, the remaining 1-2% ignore it until other problems are created.  Predicting how many people will hit something or foul a lobster pot and then remember that when they lose a reverse roller sometime later is almost impossible, but we beefed up the reverse rollers about 6 or 7 years ago to virtually eliminate the issue, and on older props we send out free replacements If you need them.  For further perspective compare an envelope with a free new roller with that you Loctite and thread in with the cost to rebuild a Max Prop after a few years of normal use, or complete replacement because you hit something.

If you’ve listened to me at a boat show, you will have heard my lubrication message.  I try to walk every customer through what’s going to happen in 2-3 years after they ignore their KiwiProp…… I’m trying to imprint a memory on them so that they know the first time they see black smoke in reverse they need to get some grease in their KiwiProp hub, not ignore it because it is an intermittent thing at first.

I’ve also noticed a few customers with issues on line suggesting ‘I grease it every year’.  I will share a story with you.  I am responsible for greasing about 6-12 KiwiProps each spring in our boatyard depending on who’s off cruising each year.  At least the KiwiProp guy has to show he’s diligent about greasing his props and while I’ve got my grease gun out why not do them all?  It takes me about a half hour to do all of them.  So after 8 or 9 seasons on my now 14 year old KiwiProps, I start having problems with my starboard engine in reverse…. how can this be?  I’m the KiwiProp guy and the grease monkey to boot?  Well as it turns out just squirting grease in until old grease comes out is not enough.  You need to rotate the hub 15-20 times at least to ensure it is moving freely, returning to its fwd feathering position, AND spreading the grease evenly around the entire hub.  Then put some more grease in!  There is no such thing as too much grease in the hub.

The blades I take off every spring, clean the shafts and pack them with new grease, a bit more work than the hub timewise, but good peace of mind.