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Old 16-12-2012, 16:52   #1
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Motor is out and now I知 confused on electrical grounding.

I have a 1976 S2 8.0 CC, on a trailer, that I am about to use as a live aboard for a couple months while I transition from UT to TX gulf (house hunting and all). The problem is, I took out the old diesel motor and have yet to replace it so, my electrical system is no longer grounded. I am cleaning up and replacing a lot of the wiring and was wondering the best option for this. It has a typical 30 AMP 120V shore power system that grounds to shore and a 2 battery bank that was grounded to the engine. I am not changing the wiring configurations that were factory installed, just updating wire, lights, and such. I would like to keep the batteries charged when plugged in to the shore and use them when day sailing around the harbor. I intend to put a motor back in eventually, unless I come to enjoy life sailing without it, but as evidence by a move don稚 have a lot of time and money on my hands now. So I値l make due with an out an outboard for a while.

Any advise on an easy temp solution or am I over thinking this and should I just ground back to the batteries?

Note: DC system runs a fridge, water pump, 4 interior lights, radio, depth sounder, knot meter, and autopilot. Though I would only be running minimum systems for day sails and AC in port.

Thanks for your time.
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Old 16-12-2012, 16:55   #2
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Re: Motor is out and now I知 confused on electrical grounding.

At its most basic level the engine block is just a big chunk of metal. I'd just securely mount a terminal block in the approximate position you want to end up.
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Old 16-12-2012, 17:47   #3
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Re: Motor is out and now I知 confused on electrical grounding.

All you really need for a ground in a boat is a place for all the return lines to come back to the negative side of the batteries As xymotic said, mount a terminal block and run all the negative wires to it, connect a fairly heavy line back to the negative side of the battery. If you set it up in a good location, when you finally get around to reinstalling an engine, you would only need to run one more wire from the terminal block back to the engine block. Making the reinstall that much easier.
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Old 16-12-2012, 18:10   #4
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Re: Motor is out and now I知 confused on electrical grounding.

Correct me if I am wrong but connecting the ground to the engine block is just a simple way of getting the ground to the propeller shaft and then to the water.
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Old 16-12-2012, 20:09   #5
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Correct me if I am wrong but connecting the ground to the engine block is just a simple way of getting the ground to the propeller shaft and then to the water.
That's what I've been reading and the reason I had some concerns about removing that feature. But shy of dangling a ground wire under the boat to simulate grounding to earth there would be no way to replicate without engine, shaft, prop.

Thanks for the advise all, it's comforting to have some conformation before when in doubt.
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Old 16-12-2012, 20:29   #6
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Re: Motor is out and now I知 confused on electrical grounding.

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Correct me if I am wrong but connecting the ground to the engine block is just a simple way of getting the ground to the propeller shaft and then to the water.
OK, I think that you are wrong!

There is no need to have a "ground" through the shaft to the water, and indeed, boats with a flexible coupler in the drive train have the shaft isolated from the engine.

However, most setups use the engine ground to complete the circuit for the starter motor which is grounded through its casing.

Cheers,

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Old 16-12-2012, 21:35   #7
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Re: Motor is out and now I知 confused on electrical grounding.

There are 3 "grounds" on a boat. The battery ground or neg terminal is unreplacable if you want to use anything involving 12V. All the 12V negatives must terminate here. 110V needs a ground "to ground", this is the 3rd terminal on your 3 prong plug shore power cord. Your metal thru hulls are connected with wire to a large zinc, this is a "ground" to water preventing electrolysis. Your earth ground to water for anything other than preventing your underwater metal from getting eaten up is wrong. Good luck.
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Old 17-12-2012, 03:38   #8
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Re: Motor is out and now I知 confused on electrical grounding.

I recently installed a new Beta 28 with a flexible shaft coupling. The dealer told me that there was no need to ground to water, and in fact it would just increase electrolysis. Just ensure the engine and battery negatives are all grounded together. No problems so far in the first year.

It makes sense, because of course in an airplane there is no ground to the earth or water. If that is a valid analogy.

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Old 17-12-2012, 05:45   #9
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Correct me if I am wrong but connecting the ground to the engine block is just a simple way of getting the ground to the propeller shaft and then to the water.
Creating a path to ground for the starter motor is the main purpose.
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Old 17-12-2012, 06:29   #10
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Re: Motor is out and now I知 confused on electrical grounding.

Even though I have a flexible coupling on my drive train, it remains grounded to the water via a wire going from one bolt to another across the coupling. Also all the bronze thru hulls are grounded to the water. DC ground and AC ground are all tied together.
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Old 17-12-2012, 06:55   #11
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Re: Motor is out and now I知 confused on electrical grounding.

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Originally Posted by The Way View Post
I recently installed a new Beta 28 with a flexible shaft coupling. The dealer told me that there was no need to ground to water, and in fact it would just increase electrolysis. Just ensure the engine and battery negatives are all grounded together. No problems so far in the first year.

It makes sense, because of course in an airplane there is no ground to the earth or water. If that is a valid analogy. Fair winds, The Way
How does a main hull anode "see" the prop and shaft? also what about the rudder shaft, how is that protected?

Pete
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Old 17-12-2012, 13:45   #12
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Re: Motor is out and now I知 confused on electrical grounding.

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How does a main hull anode "see" the prop and shaft? also what about the rudder shaft, how is that protected?

Pete
Pete,

I don't have a main hull anode. I do have zincs on the prop shaft underwater, and on the bronze rudder shoe, which protects the bronze rudder shaft. (I hope!!)

At every haulout I check the all underwater bronze pieces, including thruhulls and their bolts, for electrolysis (by scratching them). So far, no problems.

After much reading, I'm on the side of not bonding all the underwater bronze together, so that's why I check each one (I have only two underwater thruhulls, and two for the cockpit drains above the waterline).

I check the bolts because I've been told they electrolyze before the thruhulls do, and of course are smaller and so could fail faster.

Fair winds,
The Way
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