Mounting junction box on my aluminum boat

[lindy46]

I’m getting ready to mount my 1959 Evinrude Lark on my 1959 Crestliner. I’m wondering if I can mount the junction box for the motor directly on the aluminum or do I need to insulate it? I could install a wood plate between the aluminum and the junction box. Is this necessary? I’ve never worked on an aluminum boat before. All my experience has been with fiberglass.

[frankr]

No problem with mounting on the aluminum.

I stand corrected with a piece of humble pie. Neg battery cable is connected to the junction box base. Hull should not be used as a ground path.

• This reply was modified 4 years, 2 months ago by frankr.

[lindy46]

Thanks Frank

[johnny]

OMC advises to insulate the junction box from the aluminum hull as well as the motor. You can check to see if anything is grounded to the hull by checking, with an ohm meter, between the negative terminal of the battery and the hull.

• This reply was modified 4 years, 2 months ago by johnny.

[lindy46]

Well, the motor mounts to the aluminum transom of the boat so wouldn’t that be grounded through the negative battery cable anyway?

[Mumbles]

The powerhead down to the gearcase use rubber mounts which insulate it from the transom clamp assembly. That’s why some motors such as 9.9’s use a wire to bond everything together. Not sure about the continuity path in your Lark.

[dave-bernard]

If you are worried just use a block of wood to mount it to.

[frankr]

I think it would be very difficult to prevent any electrical contact between junction box, motor, and any other components from the boat.

[lindy46]

I had a plastic block on hand so I mounted it on that. I checked and the transom clamps are isolated from the engine on that particular motor. Figured I’d play it safe.

[outbdnut2]

Since there is already a negative copper battery cable running to the motor, most or all of the starter current will follow the lower resistance copper cable instead of the aluminum boat, and, as has been said, it may not find a path through the aluminum at all. I have mounted the box directly to aluminum on several boats over the years with no problems. In addition, it is mounting aluminum to aluminum, so no problem with galvanic action caused by unlike metals and moisture.
Dave

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