Hookup for Electric start on aluminum boat

[olcah]

Looking hooking up electric start to an RDE-18 on my aluminum boat. Saw on another site that connecting the battery negative to the motor can cause the boat to corrode. Discussion was that as the motor is usually electrically connected to the aluminum boat, the entire boat becomes a negative electrode.
Is that correct? My boat spends the summer in a fresh water lake. If so what can be done to prevent corrosion?
Thank you,

[auldscott]

I had an aluminum boat that was heavily pitted below the waterline, apparently the result of galvanic corrosion before I bought it. It spent its life in acid water in upstate NY with an electric start motor on it.

Not having a better solution, I would install a master cutoff switch on the battery and only turn on the power when the boat was in use.

[frankr]

Voo-doo, I say. Of course you connect the negative to the motor. And yes the motor is connected to the boat. So???? Now there would be a problem if you were to dangle a positive wire in the water. But you weren’t planning on doing that, I don’t think. On the subject though is that you should resist the temptation to use the boat as a ground for lights and stuff. That’s just bad practice.

OK, I expect to get some backlash on this, so have at it.

[fleetwin]

Not from me Frank. Needless to say, one must be careful when wiring an aluminum boat because it could become a problem if there is stray positive current in the water. But, the same problem will occur on the lower unit of an outboard/stern drive if there is stray positive current, faulty shore power wiring/units can cause this as well.
Improper antifouling paint on an aluminum hull can cause a problem, due to dis similar metal corrosion, this will occur on outboard/stern drive gearcases as well.
I guess the only solution is to never launch the boat!

[garry-in-michigan]

Salt and polluted water corrosion has always been a problem, Even with non electric start motors. In 1956 one of my Michigan co-worker’s dad took a two week Florida vacation with a two year old Super Fastwin on a wood boat. He docked the boat at a salt water Marina. It had sat with the motor down for three days when he decided to go fishing. He noticed a oil slick on the water and when he tilted the motor up, the black spaghetti seal was hanging out of the side of the gear case. He said he felt a tingling sensation when he touched the motor. It turned out the neighboring boat had a battery charger plugged into a socket that was improperly wired. Such faulty wiring has been known to electrocute swimmers. It also proves that non-electric motors can be effected by corrosion.

If you are going to keep the boat in polluted water, mount a sacrificial zink anode on the outside of the transom below the water line. . . 😉

[jerry-ahrens]

Wow, interesting story Gary. I can’t tell you how many skegs that I’ve seen rotting off boats that are up, on a boat lift, and have the skeg hanging in the water. Some of them that I’ve seen [here on Lake of the Ozarks] are nearly completely eroded or rotted away. As Gary has pointed out, this is most likely due to stray current of some sort around the dock. Most of these docks were wired by do it yourselfers, and hence the problem. Here on Lake of the Ozarks, we have had several people electrocuted while swimming, over the past several years, and sadly, some of these were children. This has caused most dock owners around here to have a licensed electrician rewire/repair their dock. The electricians around here were swamped by the abundance of work. Just about every walkway down to the dock that I’ve been on lately has ground wires along with GFIs to everything. I’ts a shame that people had to loose their life for this stuff to be fixed right.
Anyway, back to the original question about grounding an aluminum boat. I agree with Frank and Don. The outboard must have a direct ground to the battery. This has always been the case, even on a brand new rig today. All acc. such as bilge pump, navigation lights, horn, etc. must also be grounded to the battery. This can be done by hooking directly to the battery, or with the use of a ground buss, that of course must be connected to the battery negative post. Do not ground any accessories to the hull of an aluminum boat, and you will be good to go.

[jerry-ahrens]

I’m also a big fan of a battery switch. Maybe an overkill for the vintage motors we are discussing, but it is a nice accessory. If you want to put this in an aluminum boat, obviously you will need to attach it to a piece of plywood, etc. to prevent it from shorting out. http://www.perko.com/catalog/category/battery_switches/

[PugetSoundBoater]

I think have seen rubber transom protective pads that are fitted on the transom, then the motor goes over that. This would not do any good if the motor was bolted through the transom or if the rubber pad had worn. The pad would of course have to cover all three sides of the transom, inside, outside and top edge.
A battery isolator switch is always an important safety feature. How do we prevent corrosion if you want to leave the bilge pump powered while moored, a separate battery for the bilge pump?

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson

[frankr]

Anybody is only kidding themselves if they think they can insulate the motor from the boat. The water is a "wire" connecting the boat and motor. To prove it, just connect an ohm meter between the motor and boat. There will be some amount of continuity, depending on conductivity of the water. Only distilled water (pure H20) is non-conductive.

[billw]

Even here in salt water areas, negative ground engines on aluminum boats are the norm. The only time you see any problem is when there is no proper anode; and even then, you get corrosion from dissimilar metals, not the battery. Or, UNLESS there is a wiring PROBLEM, such as a positive cable with bad insulation, sitting in bilge water. The constant feed wire to a bilge pump’s automatic float switch, with the inevitable 65 repair butt connections, is a prime example to be aware of.

Regarding Gary’s story, this is more common than you think. Go to any large boat yard or Marina and observe all the shore cords dangling in the water. That’s fine as long as the insulation is good……but who wants to take that chance? Also, there is no shortage of DIY guys and professional hacks, that should not be messing with 120/240 voltage on a boat. There is no way in a million years that I would swim among boats at a marina.

Long live American manufacturing!

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