The Blonde Zinc Replacement

[Andrew Troup]

Originally Posted by fstbttms

You know what? It doesn't take a rocket scientist to determine that not every new idea is a good idea. ..... In this case there were no raves of enthusiasm about what she is doing. ....

It follows from your statements, specifically from the qualifiers I underlined, that you must be aware of a number of threads on this forum where a new idea was met with "raves of enthusiasm" ....

or even widely acknowledged as possibly having some merit.

It would be helpful if you could provide links to these threads. I've not come across any.

[Stumble]

Cal40,

Manganese Bronze is used almost exclusively on ships propellers. Not boat propellers. These props are so massively different than what you will see on your boat it's barely worth the comparison...

First they are huge. Absolutely massive, think somewhere around 16-20" thick at the mid point. Most boat props could sit sideways in one of these monsters and not hit either side. They also have to deal with cavitation problems from the tips moving so quickly.

The other issue is simply cost. Unlike our props where we just want them to last forever, a commercial ship wants an economical solution.

There are also other concerns, like the speed at which the casting cools that have to be taken into account. Casting a part this size is its own special nightmare, requiring very precise engineering to ensure that the part doesn't rupture from thermal issues on its way from liquid to solid. This just isn't an issue with boat props, even if you have a 200' yacht, your prop is a fraction the weight of these things.

The other thing is that these ships are almost always made out of mild steel, which is just outside the galvanic compatability index of zinc anyway ( a .2v delta, where .15 is considered acceptable), so the problems they have to deal with are peanuts as compared to a private boat, where you will typically find a 304 shaft, 316 bolts, bronze wheel, Monel strut, ect... If you make it all out of the same alloy it's a lot easier to control.

[cal40john]

I have no idea what %age props are manganese bronze on rec boats but I wonder how many price point boats, or people looking for an economy prop use:

For the cruiser over 30', the 3-blade MP propeller has the blade area to get the job done. The thrust provided by the MP3 propeller not only produces cruising performance when the sails are down, but also offers excellent maneuverability while docking. - The MP3 3 blade fixed pitch propeller series for sailboats is available in diameters of 10" - 24", in a wide range of pitch. Custom sizes are also possible. The typical material for the Michigan Wheel MP3 propeller series is Manganese Bronze Michalloy K, although NiBrAl Michalloy XX (Nickel, Bronze, Aluminum) material is also available.

From:
Michigan Wheel 9" (3/4&#34 ; shaft) Bronze Inboard Propel ler

Note the Title of the Ad only says bronze propeller, only if you read the fine print do you see manganese bronze, then you have to know that this is actually brass. How many would look twice after seeing the name Michigan Wheel?

John

Originally Posted by Stumble

Cal40,

Manganese Bronze is used almost exclusively on ships propellers. Not boat propellers. These props are so massively different than what you will see on your boat it's barely worth the comparison...

First they are huge. Absolutely massive, think somewhere around 16-20" thick at the mid point. Most boat props could sit sideways in one of these monsters and not hit either side. They also have to deal with cavitation problems from the tips moving so quickly.

The other issue is simply cost. Unlike our props where we just want them to last forever, a commercial ship wants an economical solution.

There are also other concerns, like the speed at which the casting cools that have to be taken into account. Casting a part this size is its own special nightmare, requiring very precise engineering to ensure that the part doesn't rupture from thermal issues on its way from liquid to solid. This just isn't an issue with boat props, even if you have a 200' yacht, your prop is a fraction the weight of these things.

The other thing is that these ships are almost always made out of mild steel, which is just outside the galvanic compatability index of zinc anyway ( a .2v delta, where .15 is considered acceptable), so the problems they have to deal with are peanuts as compared to a private boat, where you will typically find a 304 shaft, 316 bolts, bronze wheel, Monel strut, ect... If you make it all out of the same alloy it's a lot easier to control.

[sailorchic34]

I love CF. Its better then watching republicans and democrats debate..

Well I do have 3 other prop zincs on board in my spares box, so when I get back to the salty water I'll see about having someone put one on.

I would love a titanium prop and shaft. I expect though that if I have to ask the price, Well...

I do keep up on my maintenance... except for the &^%$# prop zinc which keeps falling off and thats the &^$$ screw with it...

[zeehag]

i , for one, would like to know if that practice of placing in the screen works---please keep posted re this.

[sabray]

Still being dumb ass , if the zinc deteriorates to such extent that it cannot be maintained. Then there is galvanic action somewhere eating or transferring the electrode. Nothing left is not the design intent. Bad design bad install or electrolytic reaction. Get these right and your not sticking. zinc in place that we don't normally stick zinc.

[Sir Rondo Normal]

Simple... hope for the best until you can get a new cone anode (of the appropriate type for your application) and a new screw and re-install using threadlock.

[sailorchic34]

Will do Zee.

Oh for the question on my drive from the diver. Not no drive saver and anything like that. whoever put the engine in left only a 1/4" between the end of the drive coupling and the steps. (Its a v drive so the coupling faces the pointy end.

I did check that I have continuity between the shaft and seastrainer. Which can only be had with the wire I added, btw.. I do need a bigger wire I'm thinking too

I did come up with another way to mount the cone prop nut too. A redesign if you will. Design the zinc with an internal spring clip arrangment, Two clips 180 degrees apart, mechanically fastened to the zinc, put a 3/4" round disk on the end of the bronze carrier nut thats say 1/4" larger diameter. Then if properly designed the zinc would just slide on and clip in. The zinc needs a slightly different shape too to make the clip work.. OK so somebody make that so I can buy it In Zinc and Aluminum at least

[zeehag]

ok iam a dummy--how does prop stay on boat after zinc disappears from use and screw falls out--is there a secondary back up for the keeping of the prop??? i know some folks lost prop during cruising passages--curious...

[sailorchic34]

there's a nut and then the zinc carrier nut thingy. the cone prop zinc connects to the carrier with a screw. The bad news is as the zinc wears away it gets loose and can wobble around.

Looks like a design feature to me. So I'm trying to work out better ways to mount the zinc, without it falling off before its time.

Its different then a shaft zinc, btw, there is less contact patch with the cone zincs so they tend to wear out more from the end near the contact point then toward the prop.

[fstbttms]

Originally Posted by sabray

Still being dumb ass , if the zinc deteriorates to such extent that it cannot be maintained. Then there is galvanic action somewhere eating or transferring the electrode. Nothing left is not the design intent. Bad design bad install or electrolytic reaction. Get these right and your not sticking. zinc in place that we don't normally stick zinc.

The zinc is designed to deplete, as all sacrificial anodes are. Left long enough and everything working as it should, it will deplete 100%. Maybe Chic didn't check it regularly enough. She has not said how long it had been on there. Your assumption that because the zinc is missing, there is an issue is wrong.

[fstbttms]

Originally Posted by zeehag

ok iam a dummy--how does prop stay on boat after zinc disappears from use and screw falls out--is there a secondary back up for the keeping of the prop??? i know some folks lost prop during cruising passages--curious...

The zinc mounts on a special cone-shaped nut which is secured to the shaft by a cotter pin. The zinc itself does not keep the prop on the shaft, so loss of the zinc and its screw does not mean the prop is going to back off the shaft.

[ixtlan22]

So there's supposed to be zinc thing down there eh? I've had my boat for the last 10 years and nobody mentioned this to me...no wonder I can't get out of my slip...and all this time when I looked I just thought I had a really small prop!

[David M]

I was just trying to think of a solution for the machine screw backing out. Would Teflon tape create enough friction at the threads to prevent this? Obviously applying Blue Thread-Lock underwater would not work...but it might work hauled out.

I know what you mean Sailorchic, I used to use the zinc fairwaters (called that on ships). They were never still on there a year later when I hauled the boat out, so I started using zinc shaft collars, which did the trick.

[noelex 77]

The problem with zinc is that in freshwater it develops an insulating layer. You can remove his by periodicaly sanding the zinc, but unless you are you are prepared to do this an alternative anode material like magnesium is needed.

Your zinc in water filter will not be as effective as an anode on the prop. I doubt it will work adequately. Anodes need to "see" the material they are protecting. There needs to be a flow of electrons in the electrolite ( seawater). This will happen much less readily to a zinc in the seawater strainer then to a zinc bolted to the prop.

I do sympathise. I am good free diver, but replacing a zinc underwater while holding your breath is harder than it sounds.

The prop anodes are a very poor design. Painting around the screws of the zinc at your next hallout will stop them corroding around this area which helps stop them falling off. The wasting and consequent protection of the zinc will still occur over the central thicker area.

Hire a diver if you want your prop to last. Or learn to hold your breath a long time, relax, slightly hypventilate and try swallowing. Have someone watching out for you.