Maxi Prop - 2/3 Threads Gone on Nut !

[aquabumdotnet]

Hello everyone, this is post #1 for me!

I have a customer who has a sail boat with a maxi propeller. I got under his boat at the marina to change the maxi prop cone zinc, when I noticed that out of the three holes that accept the allen screws to hold the zinc in place, only one of them had threads. I was able to install the zinc with only one screw, because the other two holes on the prop nut don't have any threads. If I remember correctly, when I removed the old zinc there were a lot of different holes around the outer circumference of the prop nut, but only three had the proper hole configuration in order to install the anode.

When I was screwing the zinc into the nut, I noticed that only one of the three holes within the configuration had threads in it. The other two holes would not be able to hold the screws in place. This would result in extra stress in the "one" screw, resulting in the possibility that the zinc may fly off during operation, or perhaps a distortion in the pitch.

I have read around on several different forums about maxi props, but I was unable to find anything regarding such events ever occurring before. Has anyone ever seen this happen? Are there any recommendations as to how I can potentially correct the issue without having the boat hauled out, and without charging the customer too much money? Any information would help. Thank you for your time!

[Paul L]

Max props need to always have a zinc on them. If the zincs are replaced too late, they are very susceptible to electrolysis. Electrolysis in the threaded zinc holes occurs and you loose the thread. I lost the thread in one of the holes. You can have the prop sent to PYI and they will rebuild with fairly fat turn around. They re-do the blades, gears, etc.

Paul L

[fstbttms]

Find a diver who knows his way around a Max Prop (PYI in Seattle can direct you). Have him remove the end cap, blades and spindle. Take the end cap to a prop shop and have them tap new threads in all three holes. Then have the diver re-install all the parts. Total cost- maybe a couple hundred bucks.

Or, as Paul L mentioned, you could have a diver pull the prop and ship the entire thing up to PYI for a refurb. It could probably use it at this point. Total cost- $700-$1000 or so.

[aquabumdotnet]

Thank you both for the great info. I will look into both possibilities and let my customer know about his potential options.

[Weyalan]

If you need to use the same size bolts (i.e. cant go to a bigger diameter bolt) I would imagine helicoil inserts would be the way to go (or any of the similar products - recoil, etc). Otherwise, drill and tap for next appropriate thread size. (I am in the process of putting helicoil inserts into rather sub-standard 1/4" threads that are supposed to hold the goose-neck and vang collar onto the mast -they work really well).

[aquabumdotnet]

Weyalan, I would like to use the same size screws. When new maxi prop zincs are purchased, they normally come with new screws. I would prefer that over having to install custom screws and having to replace them regularly or semi-regularly. I think that helicoil inserts would be the way to go. Is that something that can be done while in the water? or would the propeller have to be removed and taken to a shop where it can be done? Also, how would helicoil inserts hold up at the end of a moving propeller, where energy stress is pretty high?

Again, thanks to all of you for your ideas and input. I really do appreciate it.

[aquabumdotnet]

Or for a quicker fix, how would you guys feel if an LC shaft collar anode was installed? (instead of a maxi propnut zinc, if room on the shaft is permitted, of course).

[Paul L]

Given the propensity for Max props to have electrolysis problems and the expense of the prop, I don't think shaft zincs are sufficient. I use a shaft zinc and and a prop zinc on mine. As far as heli-coils go, since the original problem of having no thread in the hole probably came from an electrolysis issue, I'd be concerned about introducing yet another different alloy to the mix.

Paul L

[aquabumdotnet]

That makes sense, Paul. Since you are an owner of a maxprop, would you recommend getting the holes retapped to a larger diameter over the helicoil inserts?

[Paul L]

Have you inspected the prop yourself? If the blades show signs of electrolysis and/or abuse, it might be better to just pull the prop, bite the bullet and have it re-worked at PYI. Then if you stay on top of the zincs it should last a very long time. Short of doing that, I think I'd give PYI a call and ask them about the helicoils vs the oversized tapping. As long as PYI feels it would be easy for them to bring it back down to the correct size when the prop eventually gets re-worked, I'd think this is an OK way to go. There are two sizes (at least) of the allen head screws that are used on the zincs. So if yours is the smaller size to begin with, you could just switch up to the larger size. You'd have to probably drill out the zinc mounting holes each time you changed zincs, but that would be easy.

Paul L

[aquabumdotnet]

I have inspected the prop myself and it is in good shape. No sign of blistering or corrosion, which is why I found it strange that the threading was gone. The allen screws currently installed are the smaller size (not sure the size exactly, but the diameter is pretty small, and ive definitely seen bigger.) But nevertheless, I will keep in contact with the customer and let him know about the situation (i wil probably send him the link to this thread). I am headed to that marina over the weekend, so I will make sure the one screw is holding up. Ill get a hold of PYI in the meantime and see what they would recommend.

Thanks again

[JB]

I agree with Paul. I also have both a shaft collar zinc and prop zinc on the Maxi on Dulcinea. I've always been surprised at how fast the zincs disappear, so I've "doubled up" like this since Dulcinea was new.

[Jerry Cox]

Hi
Helicioling is a very strong fix. Its used in aircraft construction to double the thread strength You should be able to take the prop apart.. and any decent machine shop should be able to fix you up with stainless helicoils. The electrolytic potential is no greater than being attached to a 316 shaft..If you have electrolosis then check your boat out for leaks..that is electrical leaks..Dont forget to note the indexing if you totally dismantle. You can go on the PYI website and it gives you all the info on resetting Maxprops should you need to.
Cheers..Jerry

[Weyalan]

Originally Posted by aquabumdotnet

... Is that something that can be done while in the water? or would the propeller have to be removed and taken to a shop where it can be done? Also, how would helicoil inserts hold up at the end of a moving propeller, where energy stress is pretty high?

It cannot be done in the water, but removing the prop is not a big or difficult job.

The helicoil inserts will be stronger than the original thread was when brand new. Any fitter ought to be able to drill, tap and fit a helicoil insert in about 20 minutes maximum, so don't "get your pants pulled down" over the price.

[fstbttms]

You do not need to pull the entire prop to do the Helicoil fix on the hard. However, you will need to remove the end cap, blades and spindle. This is not especially difficult, but may not be a job for someone who has little experience working on Max Props underwater. Also, since the prop is one one the models that apparently uses the small diameter zinc screws, you might consider tapping the holes out to accept the more common, larger screws that Max Prop uses with most of their 63mm & 70mm hub props, which is what you seem to be dealing with. But maybe that fix is no easier than Helicoilng the holes.

Let me know if you want a play-by-play on how to R&R the end cap and related parts underwater. I have done it many, many times.