Grounding Problem '98 Alumnacraft

[johnsonjunk88]

Recently installing a toggle switch when grounding to grounding lug at fuse panel. Grounding wire will ground off of the boat side walls or any other metal part of the boat. Is this normal? I thought thte boat itself should not be used or can be used to ground any electrical components. Should the boat itslef be able to used to ground anything electrical? Or should it only be able to grounded to the grounding lug at the fuse box? Do I have a problem with the boats electrical system?

 

[achris]

Re: Grounding Problem '98 Alumnacraft

It's normal for the ali hull to be grounded....

 

[turbinedoctor]

Re: Grounding Problem '98 Alumnacraft

It's normal for the ali hull to be grounded....

But it is not normal to use the hull as a grounding buss.

Durwood

 

[achris]

Re: Grounding Problem '98 Alumnacraft

But it is not normal to use the hull as a grounding buss.

Durwood

Yep, that's just DA lazy and a very bad practice...

 

[Silvertip]

Re: Grounding Problem '98 Alumnacraft

A ground to a metal hull occurs the miinute the engine is bolted on. The negative battery cable connects directly to the engine block which is is bonded via a bonding wire to the tilt bracket which is bolted to the hull. Hence the hull is grounded. But no, do not ground devices to the hull. There is a ground bus at the fuse panel so ground devices there.

 

[John_S]

Re: Grounding Problem '98 Alumnacraft

A ground to a metal hull occurs the miinute the engine is bolted on. The negative battery cable connects directly to the engine block which is is bonded via a bonding wire to the tilt bracket which is bolted to the hull. Hence the hull is grounded.

If that is the intention, the outboard installation manuals I have have completely missed that subject. Many boats have wood insulating the motor on both sides. Using mounting bolts would only touch the edge of the sandwhiched aluminum, at best, where it drilled through. Plus, all tilt bracketry is painted which would not conduct readily without scraping it off. I would think if that was the intent, a bonding wire would be attached or the manual would show where you should connect one. Maybe it is tied in with the wiring that goes back to the controls?

But, if you are grounding to the hull, I assume to reduce electrical noise, and relying on motor contact, you may want to check if you do have a good path from the the hull to motor. To me, it would be prone to have a poor connection. Outside of that possible connection, I have not seen an aluminum hull grounded, but haven't had a noise issue, either.

 

[Silvertip]

Re: Grounding Problem '98 Alumnacraft

I suggest anyone that doubts the validity of my post to disconnect the negative lead of the boat harness (the small #8 or 10 gauge) wire on the negative post of the battery and leave the large negative battery cable connected. Now use an ohm meter and check resistance between one of the through-hull mounting bolts on the engine and the negative terminal of the battery. Bets you see continutity. Next, find any fastener on the boat (a metal cleat, a bow eye, stern eye, etc) that is in contact with the hull and make the same measurement. Continuity again! A layer of paint on a metal hull boat is microns thick and is easily pierced by mounting hardware. The minute the nuts are tightened on the engine tilt bracket that paint layer is also broken and bingo -- you have a solid ground. The issue of not grounding accessories to the hull is with creating multiple ground points which can cause electrical issues (ground loops for example). The best grounding system is a single point (star) ground where everything is grounded at one point. This practice is not followed very religiously in the boating world but there are basically three ground points. 1: The engine block 2: The negative terminal of the battery, and 3) the ground buss at the fuse panel. All three of those are "star" grounds at the negative terminal of the battery. Boats with generators, shore power, and other exotic wiring schemes have more sophisticated grounding schemes but smaller recreational boats are grounded as I explained.

 

[John_S]

Re: Grounding Problem '98 Alumnacraft

"Doubt" may be too strong of word. If something is out of my experience and does not make sense to me, and after going through it, will explain my concerns, and would look to be educated on it.

A key piece to me is, if this is such an important connection, why is not mentioned in installation manuals? I assumed that maybe I was just experienced with small outboards, and the most recent only being a 1997, that maybe it was just out of what I had seen. Most small elect start outboards (less than 40hp) do not require through hull bolts, and can use just the C-clamps, as well.

But after reviewing an online manual for a 2007 90 hp did not find any slight discussion on grounding to a metal hull. In fact, the way they call out using flat washers on the bolts and silicone sealant around the hole would have even more of a potential for a bad connection.

Have you seen this covered in any outboard installation manual?

As far as manufacturing and providing good grounds, any areas of metal that I have seen that are designated as such, have a callout in the print to mask during painting and/or use a serated washer to cut into the paint. Mostly just the latter because it saves on cost. Doesn't matter how many microns it is, if it is still there it is an insolater.

But, for sake of discussion, lets say we do have a good bond between bolt and bracket. How about the bond between the bolt and the hull? Are you saying that this is relying on the weight of the engine to force contact with the edge of the sheet of aluminum? That is not a tight connection, throw some sealant in the mix, vibration, and that aluminium edge oxidizing over time, to me, spells a very poor or unreliable connection. It is just hard for me to see that this is an industry type standard.

As far as your test, since I have a boat in the garage I decided to check. From the ground point (bolt) on the engine block to anywhere else on the metal engine I get around 0.1 ohms after deducting test lead resistance. That is pushing the point through the paint. When I read any point, screw, etc on the hull from a foot to three feet away, I get 1.4 to 1.6 ohms. Again that is after deducting test lead resistance. To me, that would not be a good connection for so short of a distance. Don't know if that proves or disproves anything, but I report it as I found it.

 

[Silvertip]

Re: Grounding Problem '98 Alumnacraft

You are totally missing the gist of this discussion. 1) I am NOT suggesting it is OK to ground to the hull of a metal boat. 2) I AM suggesting a single point ground that is NOT the hull but rather the NEG terminal on the battery. 3) I AM suggesting it is nearly impossible to AVOID grounding to a metal hull BECAUSE of the bolts through the hull and the fact that the engine is grounded to the battery via the large battery cable. 4) I AM suggesting and AGREE with you that the hull ground that occurs because of engine mounting is NOT a good ground but it IS generally unavoidable. 5) I AM pointing out that just because grounding electricals to the hull is NOT recommended, that it already is grounded (however good or bad) by default. 6) Engine manufacturers have nothing to do with the construction or electricals on a boat and therefore that is why you don't see anything in the ENGINE manuals regarding this. 7) If you look at the quality of the wiring on "most" small recreational boats you should understand why they don't mention this either. Can't make it any clearer than that. I've worked on and owned a very large number of boats, all but two being aluminum and every one of them presented a hull ground after the engine is bolted on.

 

[John_S]

Re: Grounding Problem '98 Alumnacraft

3) I AM suggesting it is nearly impossible to AVOID grounding to a metal hull BECAUSE of the bolts through the hull and the fact that the engine is grounded to the battery via the large battery cable. 4) I AM suggesting and AGREE with you that the hull ground that occurs because of engine mounting is NOT a good ground but it IS generally unavoidable. 5) I AM pointing out that just because grounding electricals to the hull is NOT recommended, that it already is grounded (however good or bad) by default.

Well, I didn't get that from the earlier statement:

A ground to a metal hull occurs the miinute the engine is bolted on. The negative battery cable connects directly to the engine block which is is bonded via a bonding wire to the tilt bracket which is bolted to the hull. Hence the hull is grounded.

It sounded decisive and that it was part of the design. And your reply to my 1st post seems to be defending that it is a good connection. For the life of me, that didn't make any sense.

 

[Silvertip]

Re: Grounding Problem '98 Alumnacraft

A ground to a metal hull occurs the miinute the engine is bolted on. The negative battery cable connects directly to the engine block which is is bonded via a bonding wire to the tilt bracket which is bolted to the hull. Hence the hull is grounded. But no, do not ground devices to the hull. There is a ground bus at the fuse panel so ground devices there.


What part of that did you not understand. I merely explained what happens when an engine is bolted to the hull. That creates the ground to the hull. Nowhere in that statement did I say I approved of grounding anything to the hull.

As for your resistance tests -- they proved that a ground path exists. 1 ohm (continuity and thus a ground path) is a long way away from infinity (no continuity -- hence no ground). You proved my point conclusively.

 

[DJ]

Re: Grounding Problem '98 Alumnacraft

Silvertip is correct. I think maybe we're missing a point though.

The engine/hull relationship. While the engine is essentially grounded to the hull, that is NOT the primary path. The engine battery cables are.

You should never ground any component to the hull only. Not only is that a questionable ground, it makes for the potential of some serious electrolysis.

 

[bruceb58]

Re: Grounding Problem '98 Alumnacraft

Let's say you ignored the advice here and grounded to the hull. I am probably pretty sure, you aren't going to be using aluminum wiring and an aluminum fastener. Since you aren't, that connect point will have electrolosys and will be a resistive connection. That is just the first argument against doing it. Second is that the hull is not one big piece of metal. It is many pieces of metal all bonded together in some fashion by either rivets and/or sealant....Also not a good conductive path. Bottom line, never rely on the hull to carry any current. It can be bonded so that everything is at the same potential...that is all you need or want.

 

[John_S]

Re: Grounding Problem '98 Alumnacraft

A ground to a metal hull occurs the miinute the engine is bolted on. The negative battery cable connects directly to the engine block which is is bonded via a bonding wire to the tilt bracket which is bolted to the hull. Hence the hull is grounded. But no, do not ground devices to the hull. There is a ground bus at the fuse panel so ground devices there.

What part of that did you not understand. I merely explained what happens when an engine is bolted to the hull. That creates the ground to the hull. Nowhere in that statement did I say I approved of grounding anything to the hull.

You are missing the part that it is purely by accident. Not intentional. Your decisive use of words and going into the bonding of motor to bracket makes it appear that the grouding was intentional.

And when I mentioned installation manual, etc in 1st post, it appears you were defending that it was a good connection. No mention that the connection is again unintentional.

My discussion has just been about the motor and the hull. I did not say you approved of grounding anything to hull.

As for your resistance tests -- they proved that a ground path exists. 1 ohm (continuity and thus a ground path) is a long way away from infinity (no continuity -- hence no ground). You proved my point conclusively.

A ground is a bad ground long before in reaches infinity. My point was relying on that type of connection would make a poor bond or possibly no connection at all. I never said there couldn't be a path.

I think we can agree on:

- It is not by design.

- It happens unintentionally.

- The connection between hull and mounting bolt is poor for electrical continuity.