Zincs (Sacrificial Anodes)

Having dissimilar metals in a salt water environment is important. Life-or death. The galvanic current flow means your metal bits are dissolving. There are some clever tables providing details on how “noble” each metal (and alloy) is. The “Galvanic Series” and the “Anodic Index” show you what's happening to destroy your underwater metal parts.

This is simple chemistry. It’s inevitable. It cannot be reasoned with. It cannot be stopped. It’s relentless, ruthless, odorless, and grease-free. Since we can’t stop it, the best we can do is subvert it.

Some metals (for example, gold) barely have any chemical interactions with other metals. Then there’s zinc. It’s highly anodic, so a boat will carry sacrificial zinc anodes. In the presence of galvanic electrical flows, the zinc dissolves. The rest of the underwater metals — which are doing important work — can remain untouched. 

Until, of course, the zinc is gone, then the next most anodic part starts to dissolve. Aluminum. Iron. Copper. 304 Stainless. Bronze. Brass. etc. You can see how lack of a zinc slowly destroys your boat.

The joke about aluminum hull boats is you can recharge the batteries with the galvanic currents that arise from throwing a penny in the bilge.

Stainless steel screws in an aluminum mast? Eventually, this combination will corrode even though it’s sticking up in the air and only touched by fresh-fresh rainwater.

Red Ranger has four sacrificial zinc anodes.

  1. A standard zinc wrapped around the 1¼″ stainless propellor shaft. Awkward to replace. One of these: https://anodeshack.com/streamline-collars-shaft-anodes-zinc?attribute_pa_shaft-size=1-1-4
  2. A tiny zinc on the outboard. This has lasted years. Unless the outboard lives in the water, in which case, it doesn’t last a year. One of these: https://www.defender.com/product3.jsp?name=tohatsu-nissan-outboard-motor-replacement-oem-sacrificial-anode&path=-1|299255|2284698|2284699&id=54202
  3. A zinc in the engine cooling system. This used to last about a year. Now that we have solar panels and the batteries are *always* charging, we have more current flow and the engine zinc is good for about six months. Mr. Lehman needs an E-1 zinc pencil. Here’s what they look like. https://www.boatzincs.com/engine-sizes.html
  4. A multi-pound zinc fish. This is connected to the ground plane. Because boat ground is interconnected to the rigging, it’s a simple clamp on the backstay. This: https://www.defender.com/product.jsp?id=150598

The fish is easy to inspect. Pull it up. Look at it. How much less than five pounds does it weigh?

The outboard is easy. It’s right above the propellor. A 10mm wrench is all you need to replace it.

The others? Not so much. The shaft zinc either requires a diver or a haul-out. This costs money. I replaced one in the Bahamas with a shark watching me. I was worried more about dropping one of the tiny nuts or bolts than I was worried about being eaten by a shark. 

The engine is a messy job because the zinc is nearly inaccessible. Bonus: a half gallon of raw water pours out of the cooling system when you take out the zinc. This was today’s chore. Get a wrench on this zinc to see what condition it was in.

Here’s the first stage of the journey. Engine room. It’s in the shadowy corner. Top Right.

Here’s the reverse angle on the engine room. Top right of the image is the exhaust riser, wrapped in asbestos tape. To its right is a little rusty-looking elbow. (The rubber hose near them vents crankcase smoke into the air intake.)

Meanwhile, under the rusty elbow… 

Where you can’t see it… 

Is the main heat exchanger.

Here’s a view of the bottom of the heat exchanger. If you look closely by the rusty red thing on the right, you’ll see gray hair and an eye. That’s me. Taking a selfie holding my phone underneath the heat exchanger. 

That’s an 11/16″ bronze fitting that holds the zinc pencil. And. The wrench can barely turn through an inch or two. It’s a long, slow set of tiny wriggles to back that piece out. A patient amount of fiddling to get the new one threaded correctly. And a lot of tiny wrench wriggles to reseat it.

(And yes, I neglected to paint the heat exchangers Lehman Red, which is also Rust-Oleum High Heat red. They’re still primer gray.)

I think with two universal joints and an extender, I could rig up a socket wrench to get that out. As it is, the ratchet box wrench is the tool of choice.

ty  © Steven Lott 2020