zinc's

[txsurbrook]

My boat has 2 zinc's per shaft. 3 dia, at about 2.5 pounds each. Cost about 15 dol. each.
I can buy 3 1/2 dia. at 4.5 pounds each. at 19. dol. each. can any one give there thoughs as to this being ok.

[Mariner]

You can put whatever zinc configuration on the shafts that will fit. All that matters is that they produce a minimum of drag, that there is adequate material to last between replacement intervals, and that they are properly distributed to protect large metal objects. Whether you need more than one zinc to do this will depend on the size and length of your shaft (LOL). I believe they should be replaced before 50% of the material is gone.

[JFOkie]

I agree with everything Mariner has said, especially about replacing the zinc before 50% of the material is gone. If you make the change, you can always dive and check them every so often to monitor the wear.

[MikenneyUSN]

Zinc works best when the two dissimilar mating surfaces make proper contact. If there are any gaps where the surfaces meet you may get corrosion there and the zinc will render useless at that point. I would go as far as to sand the mating surface of the shaft prior to installing any zinc.

[joreyn]

All of these posts are good advice. Here is another wrinkle.

Zinc is not the "best"sacrificial metal for your anodes. Aluminum is: it will last longer, it is lighter, and it will continue to work as effectively when your boat is in brackish or fresh water. Zinc stops working in fresh water, and after two week in fresh water, it must be replaced.

Aluminum has not been the metal of choice because, properly spec'd, it was much more expensive, offsetting its superior performance. That is no longer true. Mil-spec aluminum is now available from quality manufacturers like Martyr, for virtually the same price.

I haul my boat once a year and replace the sacrificial anodes at that time. I have found that the zinc anodes were at the limit of their useful life, or even beyond it, at the one year point. The aluminum anodes had well over 50% of their mass remaining. I replace them anyway, but it's great to have the margin for error.

One additional word of advice. For any anodes connected to your bonding system, always use the same metal. Don't mix zinc and aluminum. The zinc anodes will "shoulder all of the work" for all of the bonding system until they are gone, and then the aluminum will go to work. But by that time you won't have enough anodes to fully protect your underwater metal over the long run.

It's OK to use aluminum on the bonding system and pencil zincs in your engine and cooling systems, since they are not tied into the bonding system.

[whwells]

joreyn: This is news to me. Have not even considered alum. as a choice. So will alum. do as well in salt water as the usual zincs.
As far as I know Anacortes is nearly all salt water even with the tides changes.
whwells "Howard"

[joreyn]

Actually, aluminum will outperform zinc in salt water. Do a google search "aluminum vs: zinc anodes" Look for an article by Steve D'Antonio. Covers it all.

I just hauled Blue moon on Monday. Put zinc on ast May because aluminum was not available. Zincs are at best at 50% after 10 months. Year before I had aluminum. They were better than 60% at 14 months.

[Mariner]

All of these posts are good advice. Here is another wrinkle.

Zinc is not the "best"sacrificial metal for your anodes. Aluminum is: it will last longer, it is lighter, and it will continue to work as effectively when your boat is in brackish or fresh water. Zinc stops working in fresh water, and after two week in fresh water, it must be replaced.

Aluminum has not been the metal of choice because, properly spec'd, it was much more expensive, offsetting its superior performance. That is no longer true. Mil-spec aluminum is now available from quality manufacturers like Martyr, for virtually the same price.

I haul my boat once a year and replace the sacrificial anodes at that time. I have found that the zinc anodes were at the limit of their useful life, or even beyond it, at the one year point. The aluminum anodes had well over 50% of their mass remaining. I replace them anyway, but it's great to have the margin for error.

One additional word of advice. For any anodes connected to your bonding system, always use the same metal. Don't mix zinc and aluminum. The zinc anodes will "shoulder all of the work" for all of the bonding system until they are gone, and then the aluminum will go to work. But by that time you won't have enough anodes to fully protect your underwater metal over the long run.

It's OK to use aluminum on the bonding system and pencil zincs in your engine and cooling systems, since they are not tied into the bonding system.

I would strongly agree with this. Aluminum is the way to go.

But I work for Martyr, so take it with a grain of salt.

[Mariner]

One more thing: most all of the moorages in Puget Sound and the Inside Passage would be considered "brackish" by our standards. We all think of it a being salt water, but in reality, there are hundreds of streams and rivers and even runoff dumping fresh water into the Sound, and most of our marinas are located very close (or even in) those tributaries. I often have a hard time overcoming the perception that we have purely saltwater in our area. Yes, it's saltwater (as opposed to a lake or river, which is obviously fresh water), but on the grand spectrum, most of our boats live the majority of their lives in relatively brackish water. Aluminum outperforms zinc in brackish water hands-down, and is the only anode material that can go back and forth between salt and fresh without developing a "skin" that limits it's effectiveness.

Tell your diver and yard you want Aluminum. If you don't ask, you'll just get regular zinc. Zinc is fine, and will work, but aluminum works better, is better for the environment, and actually cheaper.

[Pitou]

It's OK to use aluminum on the bonding system and pencil zincs in your engine and cooling systems, since they are not tied into the bonding system.

I'm not sure that the quoted statement is collectively true for all boats though it maybe on your boat. On my 31 TE the engine is tied into the bonding system as it was on my previously owned 28 TE. Whatever one decides, if mixing anodes you should be sure to check to see what is on the bonding system of your individual boat.

[joreyn]

There is a ton of valuable information on this subject on the Performance Metals website. They are the makers of Navalloy sacrificial anodes which have some very innovative features, such as wear indicators which give you a visual warning that it is time to replace an anode. They also appear to be the only manufacturer of aluminum pencil zincs. Spend some time on their website for sure.

I found that Go2Marine sells their products. Defender has some but does not show the full range on their web site.

[irishwake]

I just purchased a Corrosion Reference Electrode that is very easy to operate with a ohm meter. You can check all of the bonding system on your boat to make sure it is being protected by your zincs. It will let you know if any thru hulls are not connected to the bonding system and give you readings to show the difference when you are connected to shore power and when disconnected. The electrode runs about $110.00 and I felt a worthwhile investment. I just replaced the zincs on my 31TE and had a reading of 845, I will check again in about a month and see what it reads. Interesting when I disconnected my shore power the reading went up to 915.
Numbers between .750 to.950 mean you are protected for steel. Bronze is 550-800 and aluminum 900-1005

[whwells]

This leave me a little uncertain. Flattery has the same power plants as does Kevin's 8.3 Cummins 500 electronic with the bonding system hooked to the engine as well.
Spoke with my diver about alum. last trip up. He said more expensive, harder to find and alum. tends to form a "crust"
on the surface and if not scratch up often they stop working. He does agree they last longer. If they stop working well that is bad and may explain in part the longer life.
Anacortes, Wa. is salt water but may have some fresh water as well,. but not much.
Seems like the movement is toward Alum. but is it the best idea?
whwells "Howard"
x 35te Albin Sportfisher/flybridge
2006 Sabre 42 Flybridge

[joreyn]

The reason aluminum forms a film is that it is the wrong alloy. There is a very specific alloy referred to as Mil Spec followed by a number. It includes 5 percent zinc and a trace of iridium.

Actually, zinc forms a film of zinc oxide when in fresh water.

Last point, aluminum is virtually the same price, which means it is less expensive since it lasts longer.

What your diverse told you was true many years ago.

[whwells]

joryen: Suspect my diver is just old fashion and does not want to make changes. I use Underwater Services who keep their vans at Anacortes Marina The son is a young diver but he follows the old guys recommendations. Wondering if I make the change if the engine zincs are also available in the alum. As others point out it is probably a mistake to change the boat hull zincs and stay with the engine lead base where the system is bonded. Will try to corner my diver for more explanation next trip. Where are you buying your alum. zincs?
whwells "Howard"