ABYC requirement for DC & AC ground

[David M]

If your engine is connected to your shaft and then to your prop, your engine is grounded to Earth....since water (especially salt water) conducts electricity.

[Trim50]

Nope...not necessarily. I have a 1.5" thick Nylon plate between my transmission output and my prop shaft. It electrically isolates the engine from the shaft. It has worked for 30 years now and I do not have electrolysis issues with any components on my engine...not even my heat exchangers.

[island trader]

everything needs a good path to earth. just like lightning it finds a way home, so why not give the system a good way home. then no troubles mate...

[Fishspearit]

Ok Trim50, does your boat have a bonding system which ties your through hulls and tanks together? If so your engine is also connected to earth through the fuel tank bonding and through the fuel lines. Just in case you don't think that the bolts holding your shaft coupling are providing an electrical connection between transmission and shaft, or that your coolant system is a path to the water.

[hellosailor]

My understanding is that over the years a number of repsected professionals have disagreed as to which grounding scheme is best. Apparently there are (as noted) tradeoffs and drawbacks to every scheme, whether you combine or isolate. ABYC is simply one standard from one group, if you need to satisfy your insurer that you have met their standards, you do things their way. If you have an intimate knowledge and understanding of your boat, and you prefer to do it another way...that's your option.

Most of us understand the purpose of traffic lights, and yet we still jaywalk every day. Sometimes, right in front of policemen, too.

[Trim50]

Fuel tank is in the fiberglass keel...and thru-hulls are not bonded together. I've talked with my friend that owns a Swan...he says his boat is set-up the same way.

[Tropic Cat]

Originally Posted by Trim50

I would hope everyone has an isolation plate between their engine and shaft...I do. As such, the engine is isolated from earth.

If the engine is isolated from ground, how do you conduct a lightning strike to ground?

[DeepFrz]

Joli, I think you should read this article.

Professional BoatBuilder - April 2006/May 2006

Europe allows the AC/DC ground connection to be broken only if the boat is protected by a GFCI. ABYC mandates the connection be made.

[Trim50]

Originally Posted by rickm505

If the engine is isolated from ground, how do you conduct a lightning strike to ground?

I've done enough research to know that my engine will have nothing to do with conducting a lightning strike to ground. The only thing that is going to protect your boat from a lightning strike is a good insurance policy. Of course some will argue this point I'm sure.

[Maine Sail]

Originally Posted by Trim50

I would hope everyone has an isolation plate between their engine and shaft...I do. As such, the engine is isolated from earth.

The engine on a boat still has a raw water intake and as such it is electrically still connected to the earth via this intake not to mention that it's connected to the DC system which is usually grounded too.

How are you isolating the raw water intake? Where does the ground for the starter and alternator end up? Just curious..

[Trim50]

The starter and alternator are grounded to the engine which is cabled to the negative bus of the battery system...has nothing to do with earth ground.

The raw water strainer rises just above water level. I believe (but not sure) that when the engine isn't running and pumping raw water, a separation occurs (due to gas diffusion from the water) in the outlet line of the RW strainer which rises sharply 6 more inches above the strainer before it turns downward towards the engine raw water pump.

However it works, it works well.

[Tropic Cat]

Originally Posted by Trim50

Of course some will argue this point I'm sure.

You're right.. I could argue the point... but I won't

[island trader]

trim, you should read the article from deepfrz post, expains it very well. if I take a lightning strike I want it to go out my prop shaft and not my water intake through hull, the hull would be gone, and so goes the boat. worked on several that took strikes and just replaced some wireing and elecrtonics. the boats still float. and have been shocked by faulty hvac systems when I was leaning against the eng and touched the unit, found ac and dc ground not tied together. but it's your boat and life, do what you will...

[Trim50]

Lightning strike is a completely different subject and comes in all shapes and voltages making it impossible for a single theory for protection to cover. My theory is insurance

[island trader]

it's all a form of electricity, some we can control, others we stand and watch...
in a safe place