Re-installing partial bonding system

[Redhook98]

I had my MT 49 RPH out for new cutlass bearings, paint and a few other maintenance issues recently. I had the yard put on new aluminum anodes on the shafts, rudders and struts. In the two week period in the water before it was yanked out again, there was noticeable wear on the anodes. I am on the middle Potomac so it is fresh/brackish water situations.


I have no bonding of any kind currently in the boat. It was removed by a PO. All external metals were protected only by the zincs attached to them. No signs of any corrosion issues right now. I installed two separate galvanic isolators (one on each power input). The PO had installed one incorrectly and the other line didn't have one at all.



My idea is this. I had them drill the transom and install a Divers Dream aluminum anode. I am planning on connecting the shafts (via a shaft brush), the struts and rudders to the transom anode. There is a 50-ohm separation between the trannys and the shafts, so those are not in the equation. Only the below water line exposed metal will be connected to the new bonding system. This is only for corrosion control. Not concerned about normal thru-hulls as they are just isolated chunks of metal and are not feeding the issue.



Is there any reason this would not work and extend the life of my anodes?


With just the aluminum anodes right now, using the proper test anode (silver-silver chloride), I am getting readings of -.6 to -.700 volts of activity at each shaft, rudder and strut. These should be around -1.1v. Theoretically, the addition of the large anode to the equation should get me there.

 

[Redhook98]

Also I am not trying to start a bond/not bond war here. I have not real corrosion issues. Just trying to get my anodes to last longer and protect everything.

 

[O C Diver]

First, I would find the cause of the deterioration of the anodes. If you're not using the boat, and you're sure your electrical system isn't putting current in the water, you might want to check and see if a neighbors boat is dumping power in the water which is eating your anodes. In 2 weeks, you should have seen very little deterioration.

I put a big aluminum plate on my transom and tied the rubber shaft, engine, DC negative, fuel tanks, bronze skeg, generator, bronze strainer, raw water distribution manifold, bronze stern bearing holder and two bronze seacocks to it. I considered the shaft brush and read enough to decide not to. Fine on ships, maybe not the best choice on our size boats.

Here are before and after pictures of my transom anode. Hull gets scrubbed once a month in Florida. This winter we've had little rain, so the mildly brackish water is a little more salty. This anode has been on 1.5 years.





Ted

 

[Redhook98]

First, I would find the cause of the deterioration of the anodes. If you're not using the boat, and you're sure your electrical system isn't putting current in the water, you might want to check and see if a neighbors boat is dumping power in the water which is eating your anodes. In 2 weeks, you should have seen very little deterioration.

I put a big aluminum plate on my transom and tied the rubber shaft, engine, DC negative, fuel tanks, bronze skeg, generator, bronze strainer, raw water distribution manifold, bronze stern bearing holder and two bronze seacocks to it. I considered the shaft brush and read enough to decide not to. Fine on ships, maybe not the best choice on our size boats.

Here are before and after pictures of my transom anode. Hull gets scrubbed once a month in Florida. This winter we've had little rain, so the mildly brackish water is a little more salty. This anode has been on 1.5 years.

View attachment 102732

View attachment 102733

Ted

Quite sure the issues are not coming from my boat att is point. Investigating the two next to me.


If all you are doing is bonding things for corrosion control, why bond parts that are not in the equation if they are isolated? (i.e. thru hulls, generator, fuel tanks and DC neg?) And how are you protecting your shafts and props if not using brushes? Using just shaft zincs? My intention is to be able to go 18 months to 2 years between pulls, so want the anodes to last that long, or be easily changed in the water.

 

[O C Diver]

If all you are doing is bonding things for corrosion control, why bond parts that are not in the equation if they are isolated? (i.e. thru hulls, generator, fuel tanks and DC neg?) And how are you protecting your shafts and props if not using brushes? Using just shaft zincs? My intention is to be able to go 18 months to 2 years between pulls, so want the anodes to last that long, or be easily changed in the water.

All the items with the exception of the rudder shaft, propeller shaft, seacocks, strainer and distribution manifold were bonded from the factory. The seacocks were originally non metallic. The rudder shaft I bonded to eliminate the external anode. The rudder is fiberglass; only the shaft is stainless.

I looked at the propeller shaft brush system and was unimpressed compared to what are used on ships. Read a few articles that stressed the need to keep the shaft and brush clean to maintain very low conductive resistance. I have very little exposed shaft (requires a collar anode) and decided to continue with the external anode. Both the collar anode and the plate are pretty easy to change in the water by a diver. The plate will probably last over 3 years and the collar 2 years.

Collar anode before and after:





Ted

 

[Comodave]

I have been improving my bonding system. The original was stranded wire but with very few strands so it was pretty rigid wire. Also none of the connections were sealed. They bonded in the rudder posts and strut backing plates but wired in on one end and out on the other end of the plates so that the plates became part of the circuit instead of just hooked to the circuit. I am replacing it all with tinned #6 marine wire and adhesive lined heat shrink on each connector. And I am putting the in and out cable on the same bolt so that the backing plates are not part of the circuit but rather just connected to the circuit. It is amazing how many connectors and wire are needed to complete the system. I am waiting now on a resupply order of connectors.