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Tracuman 03-01-2006 01:27 PM

Electrical System Ground
I'm in the process of refitting a 1975 Morgan 250 Classic and am installing electrical components. I seem to have it under control, but am baffled by where I should ground the system on board to the boat. I have a very shallow bilge, and if you know this boat, you'll recall that the keel is retractable. There are some fittings controlling the retractable keel, but I just cannot find any copper plates or screws in the keel area that I can connect the ground cable to. Can I just drill down into the center of the lead keel and attach it there? I'm stumped.....

redcorvette1995 03-05-2006 04:41 PM

Using a grounding plate would be easier.
It is a metal plate with two bolts. Typically about 12" to 18" long by 6" wide.

Find a spot on the hull below the water line, measure and drill the two holes (typically about 3/8") slather on some 3M 5200, push in the plate. On the inside of the hull tighten down the bolts and attach your ground cable to one of the bolts.



yachtvalhalla 03-05-2006 07:01 PM

The ready made ones I've used are called Dynaplates.
"A matrix of bronze spheres greatly increases effective area relative to flat plates. Use them as electronic grounds for SSBs, Lorans, and Ham transceivers, or as a ground reference in bonding systems. Includes gold-plated bronze flathead fasteners and silver contact paste for superior conductivity."

West Marine has them and the 18" length model number is 196040. Pricey but effective.


marinedtcomRob 03-05-2006 09:53 PM

Hmmm, let me think now. West Marine has the 18" ground plate for "Only $397.99 USD" and SailNet has it for $251.40. West Marine's is made by Dynaplate (good company) and SailNet's is made by Newmar (see also a good company. Decisions, decisions. ;)

k1vsk 05-08-2006 07:58 PM

The Dynaplate and the Newmar brand are two very different animals, neither of which should be used as an electrical ground. They are intended solely to provide an effective RF ground (although they may not be that clear in their advertizing). If used as a DC ground and you are ever hit directly or otherwise by lightning, hydrodynamic lab tests have shown they will disintegrate.

TUNDAR4 05-08-2006 11:43 PM


sailingdog 05-09-2006 06:43 AM

Generally, the DC electrical system is grounded to the battery negative terminal. The AC ground would be a bit different, but the 12 VDC ground is the battery.

There are three types of grounding systems on a boat, and they should generally be kept separate. One is a electrical system ground either AC or DC. Another is the RF ground, and it doesn't require a connection to the ocean—a large grid of copper or bronze in the bilge of the boat will often work quite well for it. The last is the lightning grounding system, which is often done using a large flat copper strip, rather than heavy wire, as the copper strip is better at conducting the large, high-voltage static electricity charges involved in a lightning strike.

The RF ground can also use a dynaplate attached to the hull. The lightning ground often uses a large SOLID copper or bronze plate or strip attached to the hull. The Dynaplate is sintered bronze, and made up of a great number of tiny spheres, and will disintegrate if used in a lightning ground system.

Attaching the lightning ground or DC system ground to the keel is generally a bad idea. This is especially true if the keel is encapsulated in fiberglass, as many the lightning discharge will then have to make its way through the fiberglass, burning pinholes at a minimum, through it as it passes out of the the keel and into the seawater.

Faith of Holland 05-09-2006 11:30 AM

The ship's dc ground and her bonding system are integrally related, effectively grounding and providing corrosion control to all of your dc components. Forget about buying anything, and connect your battery's negative post to your anodes.

sailingdog 05-09-2006 11:43 AM

Let me clarify...

The bonding system to prevent galvanic corrosion is different from that used to create a lightning safety system, where the major components of the rigging and deck hardware are bonded together to create a protective cage and grounded to provide a path for the lightning strike.

Faith of Holland is correct in saying that the galvanic bonding system should be connected to the battery's negative post and the DC grounding system.

jared 05-09-2006 02:45 PM

What Don and Saildog said.

Technically you can have three "ground" systems aboard a boat and how they are commingled or separated is a matte of religion. In case, just in case, you change your religion, you might want to treat each of the three separately and then make sure they are only "joined" at known locations. That can also help prevent 'ground loops' that can cause galvanic problems.

The lightning ground should be direct, down the mast, out the bottom, not connected to anything else. (I don't think anyone disagrees with that.) You'll find details on the web about how substantial the materials should be, etc. If there is no exterior ground path by the mast (no external keel) then you probably want to install a heavy bolt, or bolts, through the hull at that point to provide a direct lightning ground path.

The Dynaplate used to be recommended for that, but it is a sintered bronze plate (porous metal "foam") that saturates with water. If hit by a lightning blast, it supeheats into steam and sometimes blows a hole in the boat. On the other hand, they make GREAT radio grounds. And, can be good for "bonding", which is tying together all of the underwater metal parts to prevent stray current from flowing between them in the water.

The bonding wire should run between all metal parts that extend into the water, daisy-chain fashion, clean and well secured to each.

The electrical ground normally is connected to the bonding chain--but some authorities say NOT to do this, as it can cause serious problems if you do have any galvanic issues. That's the religion part.

In any case, the electrical ground runs from each electrical device (including the engine block) directly to the battery, or to common grounding blocks and then to the battery. What you have to be careful of there, is that if you do not make direct runs to the battery but let the ground wires hop and piggyback from one device to another, sometimes you can form voltage loops (ground loops) with odd consequences.

So...whichever you are doing.<G>

If you are trying to take the lightning ground out through the bottom of the boat, I'd suggest a couple of overly large stainless steel or bronze carraige bolts, simply drilled through, seated and sealed, used for nothing else. You can of course grind and fair the heads, so they don't stick way out under the boat. remember to keep a set of damage control plugs tied off nearby, in case a strike literally does blow a hole in the boat by "firing" them out.

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