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Barkleydave
#1 Posted : Saturday, December 15, 2007 2:05:33 PM(UTC)
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Proper marine practice is to ground the 12 Volt to the hull/and or engine block. Grounding of the B M is correct. Most have a ground wire going directly from the batteries to a welded post on the forward engine bulkhead. Disimular metals are isolated from the hull. Shafts, Rudders, Through Hull fittings etc.

AC ground should NEVER BE GROUNDED TO THE HULL!. AC ground is routed through your galvanic isolator or transformer. No AC ground to the hull!

Safe Boating,
dave

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jralbert
#2 Posted : Sunday, December 16, 2007 9:05:26 AM(UTC)
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Dave: thnx for pointing that out. I also guess that after 20 years it's time to take off my ground lugs and clean them and the attachment points.
Joel Albert, Potomac MD
"Charlie B" - 1988 32' FBS
Twin 318's/FWC/16x15 nibral props
docked Deale, MD
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RiverRatt
#3 Posted : Wednesday, January 02, 2008 12:14:11 PM(UTC)
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I own a 24' Monark (now SeaArk) old DNR patrol boat. It is made out of welded 3/16 aluminum with a 260 Mercrusier IO. The Monark has a plaque next to the battery shut off that says "Do not use Hull for common ground". I noticed the Marinettes do. Who is correct? One draw back is I had a ground wire burn up on the Monark. The DNR had the marine radio wired directly back to the battery. The starter ground had a bad connection and grounded thru a 12 gauge wire to the radio and the hull. (Not a good practice to have separate ground wire connected directly to the battery without having is own fuse.)

I know there is probably no absolutely correct answer but opinions are fun to hear.

Maybe there is a difference because you cannot isolate an IO or Outboard like you can a propshaft and rudder.

Robert
"The is no dumb-ass vaccine" - Jimmy Buffet
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DiverDennis
#4 Posted : Wednesday, January 02, 2008 1:25:55 PM(UTC)
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RiverRatt wrote:
I own a 24' Monark (now SeaArk) old DNR patrol boat. The Monark has a plaque that says "Do not use Hull for common ground". I noticed the Marinettes do. Who is correct? Robert


There should be only one grounding point for your entire electrical system. On most boats it is the engine block. All other grounds lead to that point.

Most accepted standards say don't use the metal hull as a ground as it will lead to galvanic corrosion. Some people will say this is not true. It's been debated for many years.

On larger boats the builders put in a grounding strip, usually a large cable or metal bar running the length of the boat which is connected to the block. All ground wires go to the grounding strip.

In the new Pro Boatbuilding there is a letter to the editor that mentions, ".....using the engine block as the DC ground is problematic" and can lead to "ground loop currents that in turn can lead to stray-current corrosion on board the vessel" and, ".....the fact that the ABYC still refers to the engine block as the primary negative reference simply points out that the standards need updating"

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marinettejoe
#5 Posted : Wednesday, January 02, 2008 4:33:55 PM(UTC)
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Diver Dennis is quite correct. A COMMON Ground would use the hull as a 3rd wire (like pipes in old buildings), just connect it to the nearest point. One place only. Aside from corrosion, this also causes hum from ground loops in radio and audio equipment.

Unzinced ships sink at slips. yep
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