Zinc / Magnesium / Aluminum - Anodes

Boating Friends

I’ve an anode query I’m looking to solve...

Maybe a Forum “Anode Guru” can place this into a more knowledgeable format than what I’ve learned so far by surfing the internet... therein reading Pascoe / Wikipedia / And, several other reviews regarding what type anode material to use in fresh or salt water conditions. In some but not all anode reviews it categorically states that zinc is simply NO GOOD to use and offers little protection in fresh water; and should only be used in salt water. And, that magnesium only should be used on inboards in fresh water. In other reviews it is said that zinc is OK in fresh water as long as the build-up layer is often cleaned (scraped / wire brushed) off its surface. Seeing as I have zinc on our currently freshwater located Tollycraft Tri Cabin I seek to find an authorative answer to this circumstance... from boaters that have years of practical boating experience and some use-time/background with anodes in fresh water.

Zinc / Magnesium / Aluminum anodes: For fresh or salt water applications – which has the best-protective-qualities? And, if its surface is cleaned regularly, with the boat kept in a not too electrically charged location, does zinc protect well enough in fresh water?

Starting April 2009 is the first time I’ve moored an inboard boat in fresh water rather than salt water. While still in salt, just before cruising into fresh water, I placed new Zinc at all locations I felt applicable, i.e. shafts, rudders, trim tabs, and a thick divers-dream block on transom wired throughout, with new pencil zinc in each engine’s heat exchanger and in the hot water heater.

Luckily we berth, cruise and anchor in rather remote areas that have reduced opportunities for electricity discharge into the fresh water. When we leave our Tolly resting at dock we off-hook both ends of the 30 amp cord, isolate all fully charged batteries and leave all breakers as well as Perko mains in off-mode... net result is the only items connecting our Tolly to the dock are four lines that hold her in mid berth. So... as I understand it, the only electric charge that could cause galvanization would need to travel through the fresh water; which I’ve read has 10X lower electric-conductivity than salt water.

Living 100 miles from the marina, we get to take our Tolly out for long weekends (3 to 5 days) about once every three to four weeks during spring, summer and, fall; and about once every five to eight weeks in winter. From Memorial Day through end of October (during our three to four week use-pattern) at anchor out I gleefully swim under boat with flashlight, mask and fins to check everything and be sure to scrub any build-up off the zincs with a fairly course bronze wire brush that has a metal scraper on its end (good ol’ BBQ brush). End of October to end of May (7 months) I don’t swim under to clean the zincs... even though months have passed, upon first brushing in spring the zinc surfaces are not too built-up, and they are readily wire brushed into a renewed clean condition. After reading in some reviews that zinc is simply not good protection in fresh water I’ve decided it’s time to ask real boaters who experience their boats in the real world of boating, in fresh water – i.e. you people!

With this fresh water routine starting April 09, making the zincs just over two years old, it appeared to me this Memorial Day they are only about 30% decreased in size but in good general condition (in salt water I needed to replace zincs annually, sometimes sooner). I see no ill colors or pits or corrosion on any metal part or fastener and the props surfaces are very smooth-clean with regular and sharp feeling edges. Both shafts remain smooth and not pitted. Also, inside the engine room where shafts come through stuffing boxes there is no creeping corrosion. So far, I’d say that in our boat’s fresh water location that relatively often brushed clean zinc anodes seem to be accomplishing an acceptable job.

Am I missing something here... or in reality if cleaned regularly are zinc anodes actually are OK to use in fresh water (as it appears to me to be the case)? Also... when I eventually do put on new anodes – should I then begin to use magnesium rather than zinc?

Any input is appreciated while I try to understand the complete reasoning and actual conditions relating to fresh water anode materials!

Cheers, W.

Thanks, Capt Bill. I appreciate your input from experience. Can you tell me how long the magnesium generally lasts in fresh? Is there a specific preferred grade of mag that is recommended? Is my routine of often wire brushing zinc recommended for mag... to help keep it at top performance level? Next anode redo I currently plan to change to mag. - Enjoy upcoming your 4th O' July!! - W.

FISH – I well understand your piss-off at what occurs to boat owners who are basically “forced” by manufacturers to use aluminum anodes. My concern goes with yours for the eventual corrosion trouble leading to replacement costs to those owners.

That said; Have you input to my base question (see my in-depth post at top of this link): What is the efficiency differential for galvanic protection of zinc versus magnesium anodes on an inboard through hull drive boat while it stays exclusively in fresh water?

Thanks! W.

TY FISH!

I will read your linked paper. I checked seacocks inside and outside last weekend. Also, as per each visit to boat, wire brushed all zincs and checked all underwater apparatus as well as all engine room and electrical devices.

Years in school can be a good addition but in no way completely makes a person... Imagination, Natural Intelligence, Intuitive Capabilities, Perception, and Perseverance/Desire... are energies that help a person float to achievement. Formal Education may also well assist – but it is NOT absolutely necessary. Depending on the forms, types, and heights of achievement one heads toward... General abilities to accomplish/perform the BASICS of Reading / Writing / Arithmetic - I believe are a requirement.

Visit the following link for some Albert Einstein Quotes – He was no dummy and not very impressed on education as a standalone feature for success: http://www.goodreads.com/author/quotes/9810.Albert_Einstein

Ciao, W.

Bill - I'm confident that brushing should somewhat reduce the lifespan of a zinc anode... however, from what I've so far learned, to leave the zinc unbrushed (in fresh water only) limits its capability for protect the more noble metals... sort of like painting over the anode. I not heard that magnesium anodes get filmed over and need brushing like zinc. Thanks for your input... Galvanization, electrolysis and anode protection from them in either salt of fresh water has many twists and turns. I'm always interested to hear from experienced boat owners on anode selection and care. – Best, W.

NYCAP - Having grown up on LI South Shore during 50's and 60's... then playing in Maine's Penobscot Bay for early to mid 70's, cruising to all points between during those years and often working in boat yards, I'm confident that zinc is the best anode for inboard through hull drive boats' salt water needs. Now however, for the first time being in fresh water (for two years), and feeling that zinc is doing a good job as long as I frequently brush its surface clean, I'm feeling that upon next anode replacement I may change to magnesium; from what I've learned to this point mag doesn’t build up, needs no surface brushing, and best protects inboard through hull drives. Aluminum isn't even on my radar for use at this, but I do know plenty of boaters with out-drives who have not a clue re anodes! - Happy boat days! - W.