ground

capeannfisherman · #1

There should be no connection from the negative terminal on the battery and the hull right? I get a zero ohms reading from the negative terminal that goes to the motor and tthe hull. That doesn't seem right. I thought the electrical system was completely seperated from the hull. 2 wires going to everything. I've already found 2 other grounds and repaired. One where the wires from the running lights go through the doghouse and another on the original electronics installation. This one has me any ideas? I just had the impeller replaced are ther any wires that run down there that may have gotten pinched?
Adrian

#2

Adrian, mine is the same way. I wonder if the paint on the motor bracket or the trf gel is enough to isolate the two which would result in a "0" reading?

capeannfisherman · #3

You get a zero ohms reading also between the hull and the cable running to the motor? That means the negative terminal of the battery is connected to the hull. Doesn't sound right. But I have never checked before , maybe it is right.Anyone?
Adrian

#4

correct "0" between the neg cable connection at the motor (under the motor cowling) to the hull

Isn't the motor & boat your ground to the water?

On a glass boat it's the motor only I believe............

Off Jay's site:

Once lightning has found your boat the metal boat provides a very good conductor for the lightning's current to go to ground whereas the NON ALLOY boat does not. The strike on a glass boat may well run through the boats electrical system which, unfortunately, runs back towards the operator (you!)

capeannfisherman · #5

OK Then I can move on as I've found the other grounds which were bare wires touching the hull. No other negative cable reads 0 now.
Adrian

Ironwood Boats · #6

Question, is that 0 ohms or no continuity?

For 25 years we have run a single 2ga wire from the battery(s) negative to the hull. We call it the hull saver ground. Then we test for zero ohms.

We started doing this when we brought a boat in for bottom paint. The zincs where gone and there was electrolysis on the hull. We could not find anything wrong until we lifted the engine off, the trim pump stopped working but the battery was sill connected. The negative wire from the engine's trim pump was broken. Each time it was used the current ran out through the hull. In years since we have found more broken trim pump wires and people that have hooked up radios and pumps using all kinds of methods but no significant electrolysis.

We use tef-gel on all our electrical (never on electronics) connections even though it is not suppose to conduct electricity. In 10 years of using the stuff we have not had a problem

We use dielectric grease on any electronics and zincs.

Sincerely
John
Ironwood Boats

capeannfisherman · #7

That is zero ohms. The negative cable running to the motor is connected to the hull. If I read your post right that is the way it is suppose to be connected.
Adrian

#8

Hmmmmm...........this is interesting

capeannfisherman · #9

this is beginning to make sense. If the hull is connected to the negative terminal of the battery then if any positive wire should come into contact with the hull it would blow the fuse and keep blowing the fuse until you fix the problem.
Adrian

#10

Adrian, wouldn't that happen anyway as the motor is bolted to the hull?

capeannfisherman · #11

Is the frame of the motor grounded to the negative terminal on the starter? I thought everything on a boat is a two wire system. I know my father, way back when, used the hull of his aluminum flat boat as the ground. He tied all the negative connections to the hull. And everywhere he did it corroded a whole in the aluminum.

#12

Jeeeez........this is an interesting topic.

Perhaps some of the builders can shed some light on this??

Ironwood Boats · #13

My preference is to run everything back to the battery. To me the engine leads should go from the pos. on the battery, though a battery switch to the starter, then from the negative on the engine back to the battery negative.....A side note: we have had boats that are positive ground.

The engine can be grounded to the hull but the battery must be also be grounded to the hull. This is not my preferred way of wiring. I have looked at boats with the negative no longer making contact or even where it has been disconnected but the engine still started.

By running the all negatives back to the battery and providing one ground to the hull from each battery it provides some cheap insurance.

It is not really the wiring before the load (pump/light or whatever else) that is a concern.....that is if the wiring is sized right and it protected by the right size fuse/breaker.......a 1 amp fuse with 10 ga wire for example can lead to problems.....
.....It is the wiring after the load that I have seen to cause the most problems. If the electricity goes into the hull after the load the fuse may not blow so the electricity needs a way to make it back into the the battery.

As far as corroding holes in the the aluminum. The wire is copper, the terminals are copper or brass then you throw in a steel or SS bolt plus some electricity. It is a great way to make holes.

Sincerely
John
Ironwood Boats

capeannfisherman · #14

I'm not sure what you mean after the load. Electrons leave the negative terminal of the battery and return to the positive terminal. ( current flow)
So if any positive lead comes into contact with the hull, before or after the load its return path is still back through the positve lead to the battery. The potential of an aluminum hull in salt water is at earths ground, this is what protects it from lightning. The only rreason I can see of grounding the hull to the negative terminal of the battery is to blow a fuse should a positive wire come into contact with the hull. I don't think the hull should ever be used as a current carrier as my example above explains. Forgive me if it sounds like a lecture, I'm a teacher and can't help it.
Adrian

#15

So.......with all this info my question is why only this way on an aluminum boat, and not on a glass boat?

capeannfisherman · #16

The only possible reason I can think of is so if a positive lead comes into contact with the hull it will blow the fuse. This will protect your hull from unwanted current flow that could cause damage. You still need a two wire system on every electrical/electronic system on your boat as far as I know. maybe Jay could add something if there are other reasons to tie the negative terminal of the battery to the hull.
On my NON ALLOY sailboats they had a grounding starp running from the mast down to the lead keel to protect it from lightning., but all the electrical was wired with two wires.

Ironwood Boats · #17

I agree the hull should not be used as part of the circuit

and I have a very little knowledge of lightning and flow of electrons

So I may learn I would ask what you see happening if there is no fuse and a pos. wire contacts the hull without a wire from the battery negative to the hull.

Sincerely
John
Ironwood Boats

capeannfisherman · #18

Current will flow. From the ground connection on a boat nearby or from the earth itself, Salt water is an excellent conductor and if there is a difference in potential. +12volts from the wire touching your hull and Zero volt, earths potential. Current will flow and probably eat your zinc in short order and probably eat a hole where the wire is touching the hull. That is probly why ther is a connection to the negative terminal. I guess I just answered my own original question.