BENCH VICE

Brian K. Lind dishes advice, beyond the obvious, on the virtues of professional divers; plus, how to keep up with those zincs.

an increase in chemical properties of the electrolyte, such as the case with battery acid, or it can occur from an increase in current through the electrolyte. Errant current fluctuates in marinas coming from other boats as well as shore- and dock-side electrical infrastructure.

To combat this, we employ sacrificial anodes, often zinc, (although, increasingly, aluminum is seen as a better anode) so that we can create a sacrificial anode in the electro-chemical reaction to protect the more important metals below the waterline. Often we attach these anodes directly to our underwater metals like our props and shafts. However, there are many other underwater metals that need protection that cannot always be provided by an attached anode. For these, it is best to bond them internally in the boat, by wiring them together, and then to a large sacrificial anode such as a diver’s dream.

But sacrificial anodes should not be a fire-and-forget strategy. We do our vessels a disservice by putting new anodes on in the yard and hope they last until our next haul out. As galvanic corrosion and electrolysis are not constants, we run a risk by not regularly monitoring the situation.

Depending on the water in which you keep your boat, you may not have an issue diving under your boat regularly to inspect the bottom. However, for those of us in waters where that is a less desirable task, such as the Pacific Northwest, it is recommended that you employ a diver on a regular schedule to inspect your boat, maintain your zincs, and monitor changes in electrolysis surrounding your boat.

A good diver on a routine schedule can help to mitigate the risk posed by fluctuating errant current as well as more predictable galvanic corrosion. By setting up a dive routine to monitor your sacrificial anodes, a diving company can note increases in deterioration, ensure replacement of anodes before your important underwater metals erode, as well as ensure you have the correct anodes installed for the salinity of the water.

Bonding systems should also be regularly tested. Connections at underwater metals should be checked for corrosion and conductivity. The simplest method for this is to visually check these connections for corrosion and proper connection. You will often find these wires corrode with some regularity in places where they are exposed to moisture, like the bilge.

A corrosion test meter can be used to ensure your boat is properly protected by measuring the voltage created by galvanic corrosion through all your protected metals on the boat. While this test is best done by a marine electrician, it can be a DIY project to make sure you are providing sufficient sacrificial anodes.

Another place that errant current can come from is your own boat. A wire can chafe in the bilge and begin to leak current, a short can ground to your bonding system, improper wiring onboard or on the dock can also lead to current flowing out through your bonded system, dissipating through your underwater metals. This can harm those metals, even if bonded to a large anode (a sharp increase in current can begin to damage metals higher on the galvanic scale than your designated sacrificial anode).

A simple test of your own boat’s current can be done by disconnecting a bonding wire from a thru hull and testing the current between the two. Even half a milliampere can be damaging to important metals. One can easily find the source of leaking current by turning circuits on and off, but often a marine electrician is required to address such problems.

So, while we often pay close attention to the maintenance of our above-water systems, there is a great need to pay attention to our underwater systems as well. Make checking your bonding system part of your regular maintenance routine. Don a scuba tank or find a reliable dive service to regularly check your anodes so you no longer have to fear the unknown.

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