Electrical Question

[terry_thatcher]

When I purchased my 382 28 years ago, the prior owner had installed a shaft brush. That is, because of a flexible coupling that electrically disconnected the engine from the shaft and prop and shaft log, there is a "brush" that rubs on the stainless shaft and a wire running from that "brush" to a bolt on the engine. I have kept it all these years.

But, I now question its necessity or wisdom. The various metals on the Morgans (chain plates, through hulls, etc) are not "bonded." (Maybe not a great idea for a Florida boat, but . . .) All my through hulls are bronze. My prop is bronze. My cutlass bearing and shaft log are bronze. My gudgeons are bronze. The only dissimilar metals under water are the stainless shaft and the stainless rudder post. (I am thinking about going to a bronze shaft, but that might require a larger diameter, which complicates things immensely.) I run a zinc on my prop and before the big MaxProp, I had an additional shaft zinc. (I may try to find a smaller one to put on the shaft in front of the prop again.)

My main DC negative ground is my battery bank. The engine starting motor is grounded there. I have a galvanic isolator and an ELCI on my AC system.

So, what is the shaft brush doing except connecting the engine to my shaft, which might just encourage increased wasting of the prop zinc and mild steel of the engine components? Or even encourage wasting of the engine anode, which is an issue on Beta engines.

I have read all about how to "bond" a boat and, if done well, it might provide a way to protect against lightning strikes (although from my reading, I doubt it). But, on an unbonded boat, should I discard the shaft brush? If I remove it, the shaft and prop etc will no longer be connected electrically to the engine and the battery negative. OR should I keep it? And why? Would the ABYC standards answer this? Jim Cleary, your thoughts are particularly invited.

Thanks for any thoughts.

Forgot to mention, my new ZF transmission has a cooler, just a bolt-on aluminum box, thru which salt water from the engine system circulates. That may be subject to corrosion, of course. Does that change the analysis? Maybe it adds to the engine zinc load.

 

[jimcleary]

Terry
In all the years we owned Dana, I have read everything and anything concerning lightening protection and grounding the metal of the hull. I my opinion it all boils down to "Damned if you do and Damned if you don't". If you do ground the fittings on your boat you are saying to Mother Nature " Go ahead, strike my boat, I have provided a path for you to pass right on through with doing damage". If you don't ground and bond it all together, you are saying to Mother Nature "there is no path to ground here so go somewhere else." Mother Nature is, at best, unpredictable and not reliable to do the same thing twice. So I have chosen not to ground. It's still a 50/50 shot. In 37 years of sailing in and being anchored or moored in some pretty spectacular thunder and lightening storms we are yet to be struck.

We use a Drivesaver on the engine shaft. This is a 1" thick plastic disk that separates the engine coupling from the shaft. It has two jobs to do. The first is to isolate the shaft from the engine electrically. The second is to be a weak point in the drive system to prevent damage in the case of an abrupt shaft failure. I know this works well because I caught an errant dock like in the prop that instantly stopped the shaft. It could have easily have tore up the transmission or worse. instead the drive saver failed and saved the engine and shaft from further damage. I needed only to replace the Drivesaver.

As to the shaft brush system that you have, If you have a Drivesaver, the brush will prevent it from doing it's primary job. Thereby inviting Mother Nature to do you nasty. I would remove that system. If you have chosen to be grounded and bonded then the shaft brush needs to stay. It is a vital part of the lightening's path to ground.

I have no idea what ABYC has to say about Grounding vs ungrounding. The boats that I know that have been struck have all had a halfassed ground system. So I think the answer is to be totally grounded or totally not grounded. Not anywhere in between.

I hope this helps you approach the question better.

Jim

 

[Warren Holybee]

The ground system, bonding system, and lightning protection system, are all separate from each other.

Properly designed lightnings systems work, there is just a lot of misinformation about what a proper system is. In essence a huge conductor from the mast step and chainplates to a very large ground plate. Then isolate the electrical wires and coax that go up the mast. There is no connection to any of the boats other electrical systems or the bonding systems. They work. I know several boats that took direct hits with no damage at all. They don't always work, but they certainly make a direct hit much safer.

Any lightning grounding system or not will not have any effect at all on the likelihood of getting hit. Surprising to many, even having the tall mast doesn't seem to make a difference. Motor vessels parked next to sailboats get hit, the ground next to a tree gets it, etc. I read a paper on the propagation of lightning a while back, and it described the reason (too long for this comment), but height doesn't make any difference until about 200 feet.

Bonding is two-part. First is safety, in case somehow a metal fixture in the water becomes energized ESD (electric shock drowning) can kill a nearby swimmer. So, all fixtures are bonded to ensure the voltage potential between them is the same. The second, is that once you do that, you introduce electrolytic corrosion. So, bonding with an anode attached to the hull protects from that. If you make the mistake of connecting the bonding system to a lightning system (or if you don't have a lightning system) there are examples of lighting blowing a through-hull out of the boat and the boat sinking. There isn't much chance of our through-hulls becoming energized with 120V, so not much reason for bonding.

A wire brush on the propellor shaft is nonsense AFAIK. I know a bunch of people like to do it, but it isn't required, and you are better off having the propellor isolated. It would only be if you have a complete bonding system with everything else underwater that you would need it, and then you need the additional anodes and maintenance that comes with it.

 

[terry_thatcher]

Thanks to you both. There is a professor in Florida who had a federal grant to investigate lightening protection. He then set up a firm to market his ideas. Fairly complicated, with numerous waterline electrical dispersers all tied to the mast. I am not trying to protect from lightening. Jim, I used to have a drive saver, which is now replaced with a similar device from PYI. Made by R&D Marine. Jim, if you don't have a shaft brush, then I will probably remove mine. My new MaxProp anode seems to be wasting awfully fast, so maybe it is trying to protect the new Beta engine, which is notorious for burning thru engine zincs.