If there's one thing I've learned in my almost 20 years of cruising...it's that just because that's the way you got the boat, doesn't mean that's the way it's supposed to be.

What Jeff said.. 🙂  Some further thoughts - it seems like your vessel has some sort of bonding/grounding system installed, though it may have flaws in it from years of exposure to seawater.  Underwater metals (thru-hulls, prop&shaft, struts (keel?) rudder shaft, and any separate zincs should all be bonded (connected) together - the proper wire color is green, but black is not uncommon.  This is what should be connected to the "RF" or protection ground points on your equipment.  You should NOT connect the DC negative buss to this, nor should you connect the shore power ground wire to it (you DON'T want your vessel's bonding system to become part of the local electrical grid!).  To re-iterate:  the negative side of your DC system is NOT a ground - yes, they are often found to be connected (usually through the starter/alternator and engine block) but you DON'T want fault currents (or worse, lightning current!) using your negative leads to get to ground.

  Some marinas will have a problem with your boat if the shorepower ground connects to the ocean - we ran into this ourselves last year.  One problem area is things like inverters, battery chargers and other AC-powered pieces of equipment, which may have a "grounding" terminal or lug on them - if its connected internally to the AC ground wire, leave the other one NOT connected to your vessel's grounding!  Inverters are a particular offender in this area.

Hartley

S/V Atsa

Underwater metals, including through-hulls, props, shafts, struts (keels?), rudders, and any separate zincs, should be bonded (connected) together. The ideal wire color is green, however black is not unusual. This is what needs to be linked to the equipment's "RF" or protective ground points. The shore power ground wire and the DC negative buss should NOT be connected to this. funny shooter 2