Propeller nut anode replacement

[Bob B.]

I have replaced my propeller nut anode made of aluminum as I boat in salt, brackish, and freshwater throughout the summer.

In replacing the anode I miss placed the star washer locking tap that keeps slight pressure on the Allen bolt so the anode does not come off. I used some medium strength lock tight (removable) for the time being. I have a trip to Florida in about 2 weeks. Should I place a lock washer under the Allen bolt or am I good? I would hate to lose my anode mid trip.

Bob.

 

[BB marine]

The Star washer has two purposes,(1) lock washer (2) continuity washer. If you have a good clean surface for the anode to contact the prop nut you will have continuity so the start washer is not really needed. If you want to install a 316 SS standard lock washer for insurance that could take the place of the star washer. The use of blue lock tight should work to hold the socket head screw in place. I believe the biggest reason that the anodes fall off is it is not fit tight to the prop nut. Many times the prop nut will have high spots. When the anode is fit to the nut it only contacts a few points. The socket head screw is tightened and the anode contacts the high spots or buildup on the nut. When the anode starts to erode it becomes loose quicker and easier because of this poor fit and starts to vibrate while under way and eventually falls off.

This was my way of insuring the anode does not fall off.

Clean the nut and fit the anode to the nut and make sure it seats on the nut properly with full contact all the way around the mating surface .

Use two 316 stainless steel flat washers a larger fender washer that is the same diameter of the socket head side of the anode. Then a smaller diameter flat washer used to bridge the larger washer

Use a 316 stainless steel Lock washer.

Measure the length of the socket head bolt to make sure it is not going to bottom out on the prop shaft when tightened

Install the anode over the prop nut, inspect mating surfaces for full contact -Anode to prop nut

Install the fastener socket head screw- lock washer- smaller diameter flat washer- large diameter flat washer- tighten the fastener to proper torque ( GOOD AND TIGHT ) or around 140 inch pounds.

 

[it4llc]

Thanks for the detailed info. I'm going to be changing out my prop and thruster anodes next week. Are there any other tools that I should make sure to have on hand/any typical problems one runs into? I'm doing a short haul to get this done at a marina that's about a 50 min cruise and about an hour from my house, so I really don't want to realize I should have brought something else along...

 

[Rangas]

I just did all of my anodes this week. Other than the obvious Allen wrenches I needed a hammer and a long piece of metal to "Gently" tap off the anode that didn't want to let go of the bow thruster. I used a 20" piece of rebar but a long screwdriver will work.
Good Luck
Randy

 

[it4llc]

Thanks Randy - that's the kind of info I was hoping for. I was planning to bring a length of dowel to keep the thruster prop from spinning, and will add in a length of some type of metal as well just in case.

 

[GaylesFaerie]

What do folks think of this idea for securing the prop anode... I have some scrap copper flashing and was thinking of cutting a 1/4" wide strip long enough to wrap around the six sided castle nut base where the anode contacts. The space might be too tight for a full wrap so I thought of wrapping the flashing on as many of the 6 nut surfaces as possible so when pushing the anode on it really jams the nut on well with more surface contact than a penny. The flashing is more pliable than a penny and seems like it will make a nice secure fit.

If I understand the galvanic series correctly, and assuming the prop is bronze (is it?), then the prop is more noble than the copper based flashing which is more noble than the zinc anode so the zinc will still be doing its job. See: https://fairwindfasteners.com/blogs/news/galvanic-series-or-nobility-chart-for-dissimilar-metals . I thought of using the penny trick but it turns out most pennies these days are made of 97.5% zinc and 2.5% copper, and I didn't want the penny sacrificing away before the anode did (see: https://coincollectingenterprises.com/information/penny-facts/year-compositions/ ).

I also found a 1.25" SS washer for the end of the anode that is exactly the same diameter as the number 4 anode's tapered end. However, the original socket head screwto secure the anode is too short because the large washer covers the countersunk area where the screw head would normally reside. So I went with a 1.25" screw which fits perfect - 1.5" was too long and did bottom out on the prop shaft as BB warned. I'll also use lock tight and a split lock washer on the socket head screw.

Thoughts? Gary

 

[knotflying]

I used two pennies for years. Never lost an anode or the pennies. The Anode always had some deteriorated and I replaced it annually regardless of condition. I did have a galvanic isolator and a sacrificial zinc that I would put in the water while on shore power.

 

[GaylesFaerie]

I used two pennies for years.

Understood and good to know it works. However, I can't remember the last time I saw a penny! (kidding) Anyway, here is another possible solution. I'll see how it fares after haul out in the fall. In the meantime, I thought a picture or two would help show exactly what I'm doing:

Castle nut with red brass flashing (85% Cu and 15% Zn) wrapped on:
https://share.icloud.com/photos/0dcZ2FM ... CVT5e99xgg

Anode fit snugly over flashing and fully fastened:
https://share.icloud.com/photos/0fd2J10 ... krx-kgoM9Q

HTH, Gary

 

[knotflying]

looks like it will work just fine.