Kiwi prop fail

[S/V_Surya]

In 2005 I bought a kiwi prop, Feathering type. I have since traveled 2000 miles from Maryland to the tip of Florida with 500 hours on my engine. Boat was stored on the hard in Florida for one year. I recently launched and went about a half a mile when prop fell off. Made it back to the boat yard hauled out. I have talked to the manufacturer and he sent a list of items that would cause this. Manufacturer thinks keyway failure is the root cause. I did service the prop with grease before launching.
If it was a keyway failure I would think I would see scoring on the shaft. I see no scoring. When installed, the prop is held in place with lock nuts with red Loctite to hold in place. On the back there is a boss that is screwed into place and lightly tightened.
I am not buying their explanation, I think sitting in the Florida Heat changed the tightening characteristics. I think the boss came loose from angular momentum.
Searching archives I only see one other report of this from Anjou. Former Cruise Forum member. Her report was suspiciously similar to mine.
My prop repair person says he never heard of a keyway failure.
Thanks.

[Captsteve53]

Originally Posted by S/V_Surya

In 2005 I bought a kiwi prop, Feathering type. I have since traveled 2000 miles from Maryland to the tip of Florida with 500 hours on my engine. Boat was stored on the hard in Florida for one year. I recently launched and went about a half a mile when prop fell off. Made it back to the boat yard hauled out. I have talked to the manufacturer and he sent a list of items that would cause this. Manufacturer thinks keyway failure is the root cause. I did service the prop with grease before launching.
If it was a keyway failure I would think I would see scoring on the shaft. I see no scoring. When installed, the prop is held in place with lock nuts with red Loctite to hold in place. On the back there is a boss that is screwed into place and lightly tightened.
I am not buying their explanation, I think sitting in the Florida Heat changed the tightening characteristics. I think the boss came loose from angular momentum.
Searching archives I only see one other report of this from Anjou. Former Cruise Forum member. Her report was suspiciously similar to mine.
My prop repair person says he never heard of a keyway failure.
Thanks.

I would ask over this period of 12 years or so has the prop ever been removed and the key way checked and or the locking nuts tightened?

Key way failure on shafts is nearly always due to

1) a bad fitting key
2) A worn Key or it's slot
3) The boss was not tight on the shaft

With these Kiwi props if removing from the shaft a PULLER must be used other wise cracking of the Acetyl Nose Cone.

There are two locking screws that should be checked - normally sealed with red loctite , if these are not checked and come loose then the whole prop will drop off!!!- any one check these??

Other maintenance that should have done yearly:

1)Checking of the attachment nut and associated locking screws have not moved.
2)Check that each of the small reversing rollers are free to turn on the small stub shafts.
3)Greasing of the unit

Was the above carried out regularly by experienced people, these are good prop's but they do have a high technical requirement when servicing,


Cheers Steve

[S/V_Surya]

My bad, prop was installed in 2015. This was the first maintenance. When installed keyway was checked all was good. Fitting of the prop was also good.
I'm going to say it was number 3, boss was not tight but was not checked. That was not listed in maintenance procedure.
In retrospect, sitting in air in Florida Heat could loosen the boss. Is that my fault?

[kenbo]

My guess, and I do have a Kiwiprop since 2013, is that the two grub screws that secure the shaft nut were not tight. Or alternatively were loosened and then retightened. Grub screws should only be used once.

If you haven't lost the prop, make very sure the keyway on both the shaft and boss are not damaged, use a new refitted key, use new grub screws and use Vibratite in lieu of Locktite on both the grub screws and shaft nut. A sharp hit with an impact driver on the grub screws will set them very well.

[Cavalier]

Out of interest, were the grub-screws removed during the maintenance operation? Red loctite typically requires 24hrs to cure, needs to be applied on clean/degreased threads, and on new grub screws - I'm not sure of this could have been a factor.

Sent from mTalk

[S/V_Surya]

No screws were loosened during in maintenance. I did not check them cuz red Loctite normally needs to be heated to remove.
Also, propeller is in 20 feet of water never to be seen again.

[Captsteve53]

Ah Ok , Sorry thought it was old!

The only way really for this to come off is that first the two locking screws need to be come loose , then the that lets the main nut come of and thats all it takes, so yes agree it unlikely the key failed, more likely it started with the grub locking screws and would have to ask:

Who fitted the Prop and did they tighten the main nut enough then tighten the locking screws with the liberal use of Red Permanent thread locker, as you state it takes heat to un lock these screws (enough heat from the Sun???) suppose if it was in direct sun light maybe!!! but usually when I need to take out red loctite screws i need some serious heat (THE LOCTITE MANUAL STATES AT LEAST 550 F degrees) is it possible under the boat to reach that would be my self question

Cheers Steve

[mikereed100]

My guess is that the lock screws were never tightened on the original installation. It's easy enough to forget. I have had Kiwis for 7 years and 20,000 miles. I often remove them in the water for service and break all the rules when putting them back on. I re-use the set screws and, often as not, forget to use red Loctite. My experience had been that the set screws just don't back out on their own, especially as their threads are fouled with growth almost immediately after putting them in the water. No way is sitting in the heat going to loosen them.

[S/V_Surya]

I fitted the prop. I fitted the prop with complete manufacturer's specifications liberal use of red Loctite. All screws nuts Etc were torqued to manufacturer's specifications.
I want to stick my neck out and say that there is a design issue.
Prop depends on a chemical bond hold it in place and exposed to air seems to break down. It needs to have a mechanical connection as a Fail-Safe.

[maxingout]

When we cruised the South Pacific, one of our friend's sailboat lost a Maxiprop in American Samoa and shortly thereafter a second Maxiprop was lost in Tonga. Very expensive to lose two props. The lesson was clear. Follow the installation instructions without deviation if you don't want to risk losing props. Optimism does not keep props on the prop shafts. Doing it right with proper maintenance is critical to avoid expensive mistakes.

[GILow]

I am reading this with interest. A Kiwiprop is on my wish list if I win the lottery.

Is there no way of incorporating a normal split pin during the installation? We have a split pin on the nut holding our prop, which I think we'd all agree, is a very reliable retaining system.

[daletournier]

Hi GiLow, I'm not sure what happened here but I had a kiwi prop for seven years and did approx 2000hrs motoring ouch! You motor alot in asia. It dosent need a split pin, I just cant see how it could come off if installed correctly, that part of it is very well designed.

Sometimes they aren't fitted correctly. Eg. I had a new prop shaft turned up, when I put the prop on it binded on the key, if you didnt inspect thouroughly it would be easy to miss that it wasn't seated on the shaft correctly. One reason I do all my own work.

I don't think they are the greatest prop but they are very good and well designed for the money you pay.

[GILow]

Thank you. That is reassuring. I admit the main appeal for me is the price, but it wouldn't be all that cheap if it kept falling off.

[Neptune's Gear]

Ive had a kiwi prop for 15 years. More than 30,000 miles in tropical, sub tropical and southern ocean conditions. Never had a single issue as long as the lubrication instructions are followed. I like them, and I don't think there is any design issue.
I have had the rollers stop turning, and had to replace blades after impact. Still using the original hub.

[GILow]

Right. Well that is also very reassuring.