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Old 08-14-2020, 12:35 PM   #1
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Bow thruster zinc and prop scrape

Today was my monthly scrape and zinc job bow thruster Allen bolts came out easy enough but I could not get the zincs off to remove the props for a proper scrape. Is there a trick?
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Old 08-14-2020, 12:50 PM   #2
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Today was my monthly scrape and zinc job bow thruster Allen bolts came out easy enough but I could not get the zincs off to remove the props for a proper scrape. Is there a trick?

For only a month's worth, that sounds quite unusual. However, they can stick at times, and I've found that using a channel lock and just wiggling them a bit will break them loose.


In an extreme case, you can secure the prop so it doesn't turn (I use a wooden dowl), and turn the zinc and you'll twist off the bolt that holds the prop at the same time. I've seen corrosion "weld" them together.


Then clean the shaft, prop, etc., get a new bolt, washer and zinc and reinstall.



I, too, like to look at them monthly to catch anything my diver misses, but often it's every other month. Rarely an issue.
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Old 08-14-2020, 12:52 PM   #3
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I've had the same problem on my Side Power bow thruster every since they switched to aluminum anodes. The anode bonds to the stainless steel nut that holds the propeller on. On land, I drill a hole in the anode, screw a sheet metal screw in part way, and pop the anode off by catching the screw head in the claw of a hammer and using it for leverage. If doing it in the water, you might try a punch and hammer tapping around the perimeter.

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Old 08-14-2020, 06:49 PM   #4
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Two good ideas I didn't think about. Channel locks could work and turing the zinc and the prop off together.
I'll try that next month.
I bought the boat in March and started monthly scraping to keep up on it. I'm in Florida and the warm water and all the unpainted stainless steel is a barnacle's wet dream. Im concerned with how fast the zincs on the shaft and rudder disappear. I've been plugged into shore power for almost 2 months. Now I'm wondering if I've got some funky electrolysis going on with shore power.
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Old 08-14-2020, 07:05 PM   #5
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How long are the anodes lasting?
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Old 08-14-2020, 08:44 PM   #6
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2 inch shaft zinc and rudder zinc half gone in a month.
Hull plate zinc and bow thruster zincs almost like new. Very little gone.
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Old 08-14-2020, 09:23 PM   #7
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That seems really quick for zinc depletion.
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Old 08-14-2020, 09:35 PM   #8
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Quote:
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2 inch shaft zinc and rudder zinc half gone in a month.
Hull plate zinc and bow thruster zincs almost like new. Very little gone.
Sounds like maybe they are not all connected together. They should all show some wear, maybe not exactly the same wear rate but not some half gone and the hull anode like new. Time to break out the onm meter and see if your bonding system is in good shape. Although that is usually done out of the water. The bow thruster is itís own system and not connected to the other anodes.
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Old 08-15-2020, 07:27 AM   #9
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The following is just MY opinion and no one has influenced me.
Get a marine electrician on board. Have him check your ground system.
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