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Old 30-10-2007, 17:28   #1
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A zinc fitting question

Just replaced the prop on my boat. The new one is a bit longer in the body, leaving less room for the zinc. So much less that it will not fit. Has anyone trimmed the width of a zinc and how did you do it? How did that work out for you?

Or I could have a bit machined off the front of the prop. I measured the space at .925. That means the prop would need at least .075 removed. Assuming the thinnest zinc available is 1.00
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Old 30-10-2007, 18:56   #2
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What's more expensive the prop or the zinc?

What's more stressed the prop or the zinc?

The consequence of trimming the zinc is that there is less zinc and you might replace it quicker.

Cut the zinc - method is depending on how much you need to trim. If it's .075 I might put it in a vice and take a rasp file to it. Bandsaw is another option.

Oh - you might talk to someone about a spacer for the prop to move it aft, if that's an option.
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Old 30-10-2007, 19:03   #3
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Before giving in to trimming a good zinc have you tried to fit a zinc over the prop nut? This solution worked for me until I was able to fit a longer shaft with adequate clearance. If you have to trim the zinc. a machine shop or doit yourself with a vice and a sawz-all can do the job. Make sure you leave adequate space aft of the cutlass brg to allow for water flow.

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Old 30-10-2007, 19:19   #4
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Instead of fussing with a zinc at the prop have you considered placing a streamlined zinc on the shaft just forward of the after strut? Same protection, less hassle. I tried the propeller nuts with the built in zinc fairwater that goes over it. They always managed to fall off after a few months after the stainless steel screw that holds it on managed to corrode away the zinc causing the whole anode to fall off. For me it was a big waste of money. I just put two streamlined anodes at the forward end of the after strut..it works well for me.
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Old 30-10-2007, 21:07   #5
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Can you move the engine back just a tad? It would require realignment, but it may be better than machining a zinc every time.

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Old 30-10-2007, 22:13   #6
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Tapered shaft, prop is where it is. Not enough threads after the prop to thread on one. No after strut, there is only one place for the zinc to go. The more I think about it I've got a lot of money in the new prop and don't want to mess with it. Looks like I'm whittling on a zinc in the morning.
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Old 31-10-2007, 06:57   #7
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Sometimes a picture is worth more than any explaination.

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Old 31-10-2007, 11:08   #8
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bmiller,

When I bought my Dragonfly 1000 I had the exact same problem as you showed in the picture. The prop was within 1/2" of the cutless bearing, so I added a flexible coupling to the shaft at the transmission. The extra length got me just enough space for a zinc.


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Old 31-10-2007, 12:42   #9
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You do not have enough clearance to effectively fit a shaft anode. When underway, the shaft will move even further forward as the engien mounts flex.
You have two other choices. Mount an anode to the threads on the back of the prop. As suggested, this is not always a good choice either. The better scenario would be to mount a Zinc to the strut or any other metal near by exposed and fit a shaft brush to ensure the shaft and prop are protected. Making sure that the shaft brush is bonded to that strut/exposed metal.
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Old 31-10-2007, 13:08   #10
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Many vessels require at least 1 cm clearance between the aft end of the bearing tube and the prop for adequate water flow to cool the bearing. Shoehorning a zinc into that space could be a bad idea. Have you tried a prop nut anode?

Prop Nut Anode*

I have used these for 2 years due to a similar problem. Worked great one year, fell off the second year. Will try lock-tite on the bolt holding the anode on this time...

John
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Old 31-10-2007, 13:37   #11
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Well for now I took a little off both ends of the zinc onhand. Just about 1/8 each side. Fits with enough room between the zinc and shaft tube for water flow into the cutlass. I'm going to look into the prop nut anode next.
Thanks for all the wisdom.
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Old 31-10-2007, 15:52   #12
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prop nut zinc

This is the style of zinc I was referring to in a previous post; it provided acceptable results, uses a cotter through a castellated nut to hold in place.

Steve
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Old 31-10-2007, 16:04   #13
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Propeller nut zinc

This is the URL to the propeller nut zinc referred to:

BoatZincs.com (978-841-9978) - Discount Zinc Anodes
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Old 31-10-2007, 16:11   #14
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Thanks Steve!
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Old 31-10-2007, 16:47   #15
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As Steve B. suggested I did the same, added a flex. coupling for the same purpose. After the install I was very suprized at how much less vibration and noise.
PYI Inc. Max-Prop PSS Shaft Seal Seaview Radar Mounts R&D
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