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I love it when readers write in. Eric wrote in over the weekend with what I think actually ends up being three good questions. One of them has to do with bonding and grounding, the other anode consumption, and the third with transducers and fairing blocks. For those of you who have no idea what the bonding system on your boat looks like, the photo below shows a green wire connected to a sea strainer. That wire is there to attach the strainer to the boat’s bonding system.


So, let’s get a look at Eric’s note so you can all see what’s going on in his case:

Got a question about my 28′ Cape Dory flybridge. After my first full season with the boat I noticed my prop zinc just about gone and the two disc type zincs on the trim tabs (I installed last spring)nearly gone as well. The boat is kept on a mooring in Salem harbor all season. I also have a dyna-plate for bonding. The thru-hulls are bonded by a bare copper wire to the dyna-plate and there is what looks like #8 green leading to the rudder post. I noticed a break in the bare bonding wire with green corrosion. I was planning on re-bonding the whole system with #8 wire. Is there anything I should be looking for or should I add a zinc plate on the transom as well? BTW it’s a Chrysler 360 and no generator. Also as part of another project I am looking to add a transducer to my Garmin 3210 and was torn between Airmars tilted element or adding a high speed fairing block. The boat cruises at about 15kts? I do mostly cruising with a little fishing on the side so it will be used
mostly for depth readings at cruise and fish finding at slower speeds. Limited space is an issue for the fairing block and the simplicity of the tilted element is attractive. Will I draw too much turbulence without the fairing block?
Thanks for your time and an excellent web site.

Ok, so let’s sort through this step by step.

First of all, if your zincs (anodes) aren’t being consumed in a Saltwater environment, you should be concerned. Since Eric is located in Salem, MA I know he’s in saltwater. Is his anode consumption excessive based on what he is telling us here. Nope, it sounds like things are just right. The idea is to install enough anode mass to last the boating season. If he were using up his anodes sooner, then he would need to add another shaft zinc perhaps, or the transom zinc he mentions. Now, based on what he is telling us the rudder and post were not connected to his boat’s bonding system over the last boating season. This deminishes slightly the amount of anode mass that is needed to provide protection for all the underwater metal. So, by re-connecting the rudder, which is of course the correct approach, he will be altering what is known as the anode to cathode surface area relationship a little. This means that he may need to add another anode to the equation this season to make sure he gets a full season’s service from his anodes. This is because he is effectively connecting in more metal to the bonding system that needs protection. Another way to do this is to install another disk anode to the rudder itself, similar to the trim tab anodes, or zincs as Eric describes them. (Not all anodes are made of zinc.)

As for Eric’s Dyna-plate, understand that it really has nothing to do with corrosion mitigation. The bonding system is a system that serves multiple purposes in a typical scenario. It is also the connecting system for the boat’s grounding system. I’ll talk about that in another post here later in the week.

As for the transducer Eric wants to install, my general advice is always going to be that if you can avoid using a fairing block of any type it is a better approach than using one. Airmar’s newer tilted element transducers do a great job of making this an easy thing to accomplish.

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