I’m coming down on the side of a ground plate for LORAN, as somebody else mentioned. If it were my boat, I’d probably pull the plate at the next haul out and repair the holes in the hull.
As far as a ground loop goes, they’re pretty common in audio and RF systems; I’m going to stick with audio as that’s my experience base. Let’s say you have two audio devices a ways apart, each powered by a local AC outlet. You connect an audio path between those two devices, including a wire that attaches the ground points of each. If there’s any voltage differential between the AC grounds of the two devices (more common than you’d think, for a variety of reasons), you then get voltage trying to equalize itself over both the AC grounds AND the audio ground you established when you connected the audio run. This will manifest itself in a buzz in the audio, generally at 60Hz and its harmonic frequencies (120Hz, 240Hz, etc.). Basically any time you have voltage differential with two different paths between devices, you can have a ground loop. I also agree with Joe about having everything terminate for ground at the engine; I usually advise putting in a Blue Sea bus bar with a single large wire to the engine, then terminate the grounds at the bus bar. It makes things much cleaner, and usually much easier to work on and more reliable, as you don’t have a hole bunch of wires subject to constant engine vibration. — Fred Fred Street -- Minneapolis S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI :^( > On Apr 7, 2016, at 9:26 PM, Pete Shelquist via CnC-List > <cnc-list@cnc-list.com> wrote: > > Sounds like the PO may have been misinformed, or overly cautious, and figured > more is better. > > Someday will someone explain to me the concept/theory of a ground loop? I’m > looking at you Fred. > > > From: CnC-List [mailto:cnc-list-boun...@cnc-list.com > <mailto:cnc-list-boun...@cnc-list.com>] On Behalf Of Ken Heaton via CnC-List > Sent: Thursday, April 07, 2016 5:59 PM > To: cnc-list > Cc: Ken Heaton > Subject: Re: Stus-List Ground loop? > > Did the boat ever have a shortwave radio? > > Was a previous owner afraid of a lightning strike? > > Just guessing. > > Ken H. > > On 7 April 2016 at 18:20, Ryan Doyle via CnC-List <cnc-list@cnc-list.com > <mailto:cnc-list@cnc-list.com>> wrote: > Hey everyone, > > I am in the home stretch of re-wiring my entire boat. The wiring was in > frightening shape when I bought it back in October - much of it was corroded > and probably original, and there were numerous "bad fixes" that I didn't like > the looks of. So, I ripped it all out and started anew with a whole bunch of > Ancor marine wire, a BlueSea panel, BlueSea fuse blocks, and went about > re-wiring. > > All negative wires connect back to the nut at the back of my A4 motor, which > is also connected to my battery negatives. All good. > > However, there is one large gauge (maybe 10 gauge?) old wire going from the > nut on the back of my A4 to a nut attached to a metal plate that is attached > to the outside of the hull. This metal plate is located slightly forward and > to starboard of the front of the A4. Another wire coming from the nut over > this metal plate is also connected to a keel bolt. > > I don't see this plate or wire on the original C&C wiring diagram for the > boat. And from what I know, having more than one negative point outside the > hull will create a ground loop. > > Any thoughts on why someone did this? > > Thanks, > Ryan > Nobody's Bargain > 1976 C&C 30 mki > New York
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