Grounding when on the hard

[HOTFLASH]

So, when on the hard in the winter, how can the engine or the shaft be the effective ground connection when the boat is not in the water? Am I missing something? I disconnect my batteries in the winter--not sure if that is important. Can anyone help me understand this?

Mary

[ndutton]

It helps to know the purpose of a ground. Before we go there, is 120VAC connected to the boat during layup?

[sastanley]

Mary, When you disconnect your batteries, make sure they are fully charged. A dead or discharged battery usually won't come back after being subjected to freezes over the winter, but a fully charged battery (occasionally charged) should be OK.

I keep a small 5 watt solar panel (with a charge controller) onboard and just swap it between batteries over the winter. I used to haul them home and store them in my 45° garage, but not anymore...the solar seems to keep them up just fine over winter.

All of my opinions are also subject to your geographic area. I live in Maryland, so we get regular freezes from December to March, but only a few nights 25°F or colder near the Chesapeake. If I was up in Canada, I'd probably get the batteries off the boat since I would put the boat away and probably not visit it for months.

Neil's questions are valid too, i was just talking about the batteries themselves.

[Al Schober]

Hi Flash,
Think of the space station - lots on electrical stuff with ground connections, but they're further from ground than your boat is in it's cradle! Perhaps it's better to think of it as a 'Common' connection.
All cars that I know of today connect the - terminal of the battery to the frame. I know this wasn't always the case - there have been cars with the + terminal connected to the frame. They worked fine!
My physics prof told us that there's an 'absolute zero' temperature where all motion stops - perhaps even a puppy's barking and a woman's mouth. I don't think there's a corresponding absolute zero voltage. Voltages always seem to be measured between two points. Polarity can be one way or the other.
A lot of our A4 electrical diagnosis involves voltages, and a lot of the problems with these measurements involves the selection of the wrong points - particularly the 'ground' connection. I'll make a bit of a leap here, but I'd suggest that you're always safe if you use the - battery terminal for your 'ground' connection.
My tool kit includes a long length of wire with two alligator clips. Clip one end to battery - and the other end to my meter. Wire is long enough to measure voltages anywhere in the boat (not sure if it will reach the masthead). Gee, pump won't run (light won't light) - has 12 V to it! Checking, the other terminal also has 12 V - bad ground. Replace the ground wire, save the pump/fixture.

[joe_db]

The only grounds that will have anything noticeable change while on the hard are lightning and SSB.

[HOTFLASH]

Thanks all

Thank you all for your responses.

Sorry I did not make it clear that I have no power other than my 2- 12v group 27 flooded batteries which I disconnect from my system, and have left on my boat over winter without problem for the past 16 years. I live in Chicago where I can get to -20. I charge them completely one at a time with an ac "smart" charger plugged into yard's power while I am present for the last time in the season, usually in November before any sustained deep freeze, and then as soon as I can in the early spring after sustained thaw, never under 35 degrees. I use an ambient temp thermometer and laser reading of the batteries themselves. Of course, I test the charge from time to time as well with a meter. They have never lost too much juice over that time. My yard does not allow anything to be plugged into their power unattended. No over night stays. This plan has worked well for me for a long time.

I am outside and cover my boat with a tarp, and do not consider a solar panel is workable, or even necessary.

At my yard, Rentner Marine, which has been around since the early 40's, cannot take boats mast up. We did have one 40 ft sailboat in the yard get hit by lightening last spring through its radar mast, going through his keel and creating 1 foot divits in the ground under the keel and of course havoc with electronics. It was 15 feet from me, and within 30 feet from a 50-ft permanent large crane. Go figure! I have no radar mast and I remove all non-engine related electronics over the winter. I have no SSB radio.

My original question comes from the usually stated reason for the ground (-) connection to the engine is its connection to the shaft and the water (ground). It occurred to me there is no such water when on the hard.

Thanks for space ship and car examples.

Mary

[ndutton]

That helps a lot Mary. There is zero benefit for the DC system to be grounded to the water when the boat is floating other than a ground plane for radio. Therefore there is no benefit in providing a ground to the metals when the boat is on the hard.

AC is different and since you're not plugged in (good policy on the yard's part BTW) an external ground is of zero benefit again.

I'll spare you the agony of a lengthy post on the reasons for grounds on AC systems and fallacies about them too.

[sastanley]

I think you are smart to disconnect battery terminals in winter..with zero discharge, there should be no reason the batteries can't survive the cold. It is possible that with faulty wiring that trickle discharges could happen. Removing that chance the way you do is great.

I like your past practices, and they seem to work.

Let's just hope that there continue to be boats with radar masts around you that stick up farther in storage.

[joe_db]

IIRC, commercial ships use floating AC systems. We inherited the grounded systems from shore-side practice in houses. I have set up floating ground DC systems on aluminum boats, but it is a very large PITA to do if you don't have to.
* I didn't have any legal way to make a floating AC system at 120 volts, but we did use a transformer to make it *isolated ground* from anything on shore. Well worth the $$$ on a big metal boat.

That helps a lot Mary. There is zero benefit for the DC system to be grounded to the water when the boat is floating other than a ground plane for radio. Therefore there is no benefit in providing a ground to the metals when the boat is on the hard.

AC is different and since you're not plugged in (good policy on the yard's part BTW) an external ground is of zero benefit again.

I'll spare you the agony of a lengthy post on the reasons for grounds on AC systems and fallacies about them too.