Grounding to hull

[Stumpalump]

Everything on my boat is grounded back to the battery but the hull is metal. Why don't we ground the hull to the battery and then ground everything else to the hull? It would be easier to wire things.

 

[DrNip]

Some say it will lead to galvanic corrosion. Some say it won't.

 

[Stumpalump]

I just thought it was odd that my freshly installed trim runs fine without a ground wire and assumed the hull is the ground. I went ahead and wired up a ground to the battery.

 

[JMichael]

DrNip » Today, 10:55[/url]"]Some say it will lead to galvanic corrosion. Some say it won't.

I've also always heard it was a big No-No to use the hull as ground, although I can't say what would happen if you did it.

 

[PSG-1]

ABYC codes state that each device must have its own seperate ground wire. In saltwater, grounding to the hull is a definite no-no, due to galvanic corrosion. Also, in saltwater, the hull should have its own anode, connected through the bonding wire that's on the outboard, or, a bonding wire that goes to the negative terminal of the battery.

 

[Country Dave]

It's not a good idea,

Why would you, as previously mentioned individual components really should have a good dedicated ground to the battery or a ground bus-bar. A bus-bar that's gets its ground from the battery. If your aluminum hull is grounded you've now given every voltage wire and opportunity to short if it chafes on the hull, and if that short happens between the battery and before the fuse you have a big problem.


I don't know if grounding the hull will help promote galvanic corrosion or not, but if you take two dissimilar metals and introduce them into water "witch is an electrolyte" you've now created a battery. Aluminum by itself will also corrode on its own if introduced into water.

Just as dissimilar metals that come in contact with each other will create voltage "and that voltage is what degrades the metal", so does aluminum in water "especially in high salinity water" because the water itself has properties that interact with the aluminum and creates voltage.

 

[nlester]

This brings back memories of automobiles using the frame and body for the negative wire to the lights. When the taillights would stop working, you had to cleanup the corrosion, run a new screw through the light housing into the car body or run a wire from the negative post on the battery and loop it to each light. All of this usually happened on a cold, rainy night in the middle of nowhere. Some RV's still use the RV as the negative conductor for side marker lights. The headaches and the problems are not worth it. You don't want to be troubleshooting along side the road on the way back from the lake. Besides that, if you have a short, you boat basically be comes the hot wire. How many of us have had a short that melted the end off a screwdriver.

Even worse was when an electrician was installing conduit for house wiring and used the conduit as the common wire back to the fuse box. Even using the conduit as the ground could cause issues.

Using a dedicated wire for each purpose makes troubleshooting and life much easier and safer. Using the boat for a ground works but it has it's risk. It costs a little more for dedicated wiring but it keeps it simple and isolates the electricity.

In my opinion.

 

[PSG-1]

Well, the fact is, if your engine has an electric start, as soon as you hook it to the battery terminals, the hull of your aluminum boat does become a 12V negative circuit. And this is the reason for the anode, because even though you may take every precaution not to ground anything to your hull, your motor is grounded to the hull, and you have to deal with stray current and electrolysis.

As for house wiring, if the conduit is metal, and it is going back to a metal junction box which has a ground wire connected to it, then, the conduit does serve as ground, and this is acceptable by code. Personally, when I put in a run of conduit for house wiring, I use non-metallic conduit, and use THHN wire, not romex, and I run a separate ground wire.

 

[Country Dave]

PSG-1 » 3 minutes ago[/url]"]Well, the fact is, if your engine has an electric start, as soon as you hook it to the battery terminals, the hull of your aluminum boat does become a 12V negative circuit. And this is the reason for the anode, because even though you may take every precaution not to ground anything to your hull, your motor is grounded to the hull, and you have to deal with stray current and electrolysis.

As for house wiring, if the conduit is metal, and it is going back to a metal junction box which has a ground wire connected to it, then, the conduit does serve as ground, and this is acceptable by code. Personally, when I put in a run of conduit for house wiring, I use non-metallic conduit, and use THHN wire, not romex, and I run a separate ground wire.

Good info PSG-1

Funny you should mention that, I thought about that when I ran my battery cables to my motor so I took a test light and clamped it on battery POS+ and then put the probe on the hull in multiple locations and my hull is not grounded. My motor is on a jackplate I think it must be getting insulated from the paint on the feet of the engine mount and the paint on the transom.

 

[Ranchero50]

On mine I ended up using the hull to ground some circuits, especially lamps that used a mounting screw for ground. My motor is grounded to the hull stringer as well.

It's funny that you guys mentioned corrosion because in the Navy everything is bonded to the ships hull.

 

[Country Dave]

US Navy Littoral Combat Ship Independence,

Serious galvanic corrosion has been reported on the latest US Navy attack littoral combat vessel the USS Independence caused by steel water jet propulsion systems attached to an aluminum hull. Without electrical isolation between the steel and aluminum, the aluminum hull acts as an anode to the stainless steel, resulting in aggressive galvanic corrosion.

https://www.bloomberg.com/news/2011-06-17/navy-finds-aggressive-corrosion-on-austal-s-combat-ship-1-.html

 

[PSG-1]

Country Dave » Today, 10:20[/url]"]

PSG-1 » 3 minutes ago[/url]"]Well, the fact is, if your engine has an electric start, as soon as you hook it to the battery terminals, the hull of your aluminum boat does become a 12V negative circuit. And this is the reason for the anode, because even though you may take every precaution not to ground anything to your hull, your motor is grounded to the hull, and you have to deal with stray current and electrolysis.

As for house wiring, if the conduit is metal, and it is going back to a metal junction box which has a ground wire connected to it, then, the conduit does serve as ground, and this is acceptable by code. Personally, when I put in a run of conduit for house wiring, I use non-metallic conduit, and use THHN wire, not romex, and I run a separate ground wire.

Good info PSG-1

Funny you should mention that, I thought about that when I ran my battery cables to my motor so I took a test light and clamped it on battery POS+ and then put the probe on the hull in multiple locations and my hull is not grounded. My motor is on a jackplate I think it must be getting insulated from the paint on the feet of the engine mount and the paint on the transom.

Probably so. And it's great that yours is like this, because, that's the ideal thing to do, not have ANY voltage in the hull. But in most cases, the engine connection to the hull won't be so well-insulated, and that test light would show voltage if you tried it on most johnboats with electric start engines.

 

[JMichael]

Ranchero50 » Today, 09:50[/url]"]

It's funny that you guys mentioned corrosion because in the Navy everything is bonded to the ships hull.

Was that the ground circuit of the device that was bonded to the hull or the device housing/black box that was bonded to the hull? It was my understanding that all the devices housings were grounded to the hull to prevent electromagnetic problems such as those that might be experienced from a nuclear EMP. I think it was intended to work that same as a Faraday cage.

 

[Ranchero50]

If memory serves, pretty much everything was.

I worked on this guy: https://en.wikipedia.org/wiki/AN/SPS-49

Left side box is the transmitter, dark grey Y thingy is the waveguide that conveyed to 250kw out to the antenna.

Good times were had sliding across the coated floor in rough seas.

 

[JMichael]

Wow, that's a huge waveguide. The waveguide and associated equipment that I worked on, when I wasn't jumping out of it, was in this.
https://en.wikipedia.org/wiki/File:USS_Bagley_%28FF-1069%29_refueling_SH-3.jpg

I was an aviation electronics tech/rescue swimmer. I logged several hundred flight hours in this actual helicopter. My squadron/detachment had six SH-3G's number 721 thru 726. The waveguide used in it's on board Doppler radar system wasn't as big as my wrist.

 

[Ranchero50]

Oh, I think I flew off the ship and around the gulf to Bahrain in one of those when I got out in '95, think they called it the 'desert duck'. Fun way to spend the day until we landed on a Burke class and they loaded a dead guy in the back. I was also surprised at how much red hydraulic oil leaked out of the ceiling in flight.

 

[JMichael]

LoL, Before I got out, I had over 3,000 flight hours riding around in the back of those things so I know exactly what you mean about the hydraulic fluid. They were like a plumbing nightmare of hydraulic lines in the overhead. Whenever the ground crew got upset with one of the pilots, one of their favorite things to do was "adjust" a line fitting that was over the offending pilots seat, so that it would have a slight leak. There were times that we would land after 4 hours of flying plane guard and the pilot would have a large area of his flight suit soaked with fluid. Of course that wasn't as gross as what happened when they would modify the pilot relief tube. :mrgreen:

 

[Kochy]

I accidentally grounded to my hull by accident hooking up a cigarette lighter in the front of my boat due to a loose wire end, I went to rub a mark off with my finger (Licked it of course) Gave me a pretty nice shock, also scared the s**t out of me. So yeah wouldn't recommend it.

 

[nlester]

PSG-1 » 13 Dec 2013, 09:06[/url]"]Well, the fact is, if your engine has an electric start, as soon as you hook it to the battery terminals, the hull of your aluminum boat does become a 12V negative circuit. And this is the reason for the anode, because even though you may take every precaution not to ground anything to your hull, your motor is grounded to the hull, and you have to deal with stray current and electrolysis.

As for house wiring, if the conduit is metal, and it is going back to a metal junction box which has a ground wire connected to it, then, the conduit does serve as ground, and this is acceptable by code. Personally, when I put in a run of conduit for house wiring, I use non-metallic conduit, and use THHN wire, not romex, and I run a separate ground wire.

Using the metal conduit as the ground is acceptable but I have seen cases where they used the conduit in place of the common wire in house wiring. It gets your attention. I like a dedicated wire for everything. It saves problems and is easier to troubleshoot.

 

[JMichael]

PSG-1 » 13 Dec 2013, 08:06[/url]"]Well, the fact is, if your engine has an electric start, as soon as you hook it to the battery terminals, the hull of your aluminum boat does become a 12V negative circuit. And this is the reason for the anode, because even though you may take every precaution not to ground anything to your hull, your motor is grounded to the hull, and you have to deal with stray current and electrolysis.

As for house wiring, if the conduit is metal, and it is going back to a metal junction box which has a ground wire connected to it, then, the conduit does serve as ground, and this is acceptable by code. Personally, when I put in a run of conduit for house wiring, I use non-metallic conduit, and use THHN wire, not romex, and I run a separate ground wire.

There is a difference between your hull being grounded and using your hull as the ground leg of a circuit. Power is going to seek the path of least resistance and a copper wire will have lower resistance than an aluminum hull if it's wired correctly.