Category Archives: Galvanic Corrosion

Bow battery? Stern Switch?

Hi Kevin,

I want to add a second battery at the front of my 18 foot pontoon boat to run a trolling motor that will mounted on the front.

I would like the main motor, a 70 hp Evinrude, to charge the trolling motor battery. Battery switch

What gauge of tinned marine wire would you suggest? I assume stranded wire would be best.



Hi Artie,

If you want your 70 hp Evinrude to charge both batteries, it may be easier put the second battery at the stern of the boat and connect them together with a boat battery switch system, which you can find our on sister marine electrical site.

This will allow you to select which battery the engine is starting from and also help prevent a dead battery after too much trolling motor use.

Run the trolling motor leads to the rear of the boat and use circuit protection as close as possible to the battery for the trolling motor.

The cables that connect the batteries are short and there is no requirement to have circuit protection on them since that can be used as part of the starting circuit.

Never use the frame of the boat as the path to ground. It will cause SEVERE galvanic corrosion.

Good luck,


Bot Buddies

Dear Kevin,

Last summer, I purchased a new aluminum fishing boat. It’s great, but I screwed up by “cheaping out” at the last minute. I passed on the trolling motor package and – as you’ve probably guessed – now want to add a trolling motor.

As a long time reader, I know that you are a big fan of Motorguide trolling motors and I’ll be buying one in the next couple weeks. My question concerns the boat wiring.

The Motorguide will be bow mounted, but since I didn’t get the trolling package, the only wire at the bow is a 16 gauge pair for the Attwood LED navigation light. But, according to your boat wiring size calculator, the trolling motor should be wired with 6 gauge.

Is there any way to make the smaller wire work? I hate to start rewiring a brand new boat if I can avoid it.



Hi Sean,

Since your boat is new, you may be in luck. A lot of boat builders now use Ancor’s new Nanotech Wire. As you’d guess from the name, it uses nanotechnology to solve problems just like yours.

Simply put, Nanotech Wire matches wire size to power demand by moving copper to where it is most needed – sort of a Viagra for marine electrical.

In the past, running a trolling motor on undersized wire caused voltage drops, heat buildup and embarrassing insurance claims. But now, that same temperature increase signals Nanotech Wire to deploy an army of nanobots who quickly rebuild the harness to match the power demand. While at work, these little guys make the wire looks like a python that swallowed a large rat.

Once your harness is properly sized, the same bots then go to work on its insulation so that it correctly corresponds to standard boat wiring colors.

The patented process is called Nanotech Overload Sensing Heat Induced Tranference and it works great. The only time I’ve seen it fail is when there are so many accessories turned on that there is no extra copper available. If this happens a lot, I usually recommend the addition of a copper reservoir to supply additional material as needed.

Have an excellent day.


Nautical equivalent of “Old Sparky”

Hi Kevin,

I found your boat wiring website and would be grateful if you might comment on the following for installation of marine electrical systems in an aluminium hull boat. Its a complicated issue I know!

  • AC system includes generator, inverter and marine electrical shore power. The AC system is entirely floating,  i.e., no negative grounding and is interfaced with shore connections via an isolation transformer.
  • DC system includes house battery, engine alternator (isolated negative) and engine battery. All are grounded to one common negative pole on the hull. No other equipment is negative grounded.

I have been told that it would be better to float the DC system entirely as well (same as AC) so that there is no negative ground at all. Is this correct?Shock hazard



Hi Al,

Unless somebody went through and removed the AC/DC ground connection, it should still be intact and must remain. A boat without this connection is an extreme hazard. With an AC fault to the hull, there is no low resistance path back to ground to trip the breaker and the boat will turn into a very large electric chair.

On your boat generator, the AC ground and AC neutral are connected together on the metal engine block of the generator. The generator negative battery cable is also connected to the engine block and your DC negative system. An inventer will have the same AC neutral to AC ground connection. Your AC distribution panel should have a link between the AC ground (Green) and the DC negative on your boat.

Hull ground isolation is nearly impossible on an aluminum boat with an engine and unsafe on an aluminum boat with AC power. The engine and its underwater gear are inevitably electrically connected to the engine block and the DC negative. A positive hull connection to the DC negative gives a low resistance path back to AC ground and DC ground in the event of a fault. A DC fault to an un-grounded hull can create accelerated galvanic corrosion. The area with the positive cable connected to it will corrode to protect your engine and drive.

Hope this helps,


GI Install

Hi Kevin,

I recently received one of the Easy Add AC Shore Power systems from your Boat Wiring Store.

The system looks great…perfect for my Whaler Outrage. But, prior to installation I have a couple of questions. I have a 30 amp Yandina galvanic isolator that I plan to install along with the shore power kit.

Could you give me some idea of how it should be wired? From what I have read on Yandina’s instructions the green wire (ground) on the panel should be connected to the isolator with the other lead from the isolator comnnected to the boat’s 12 volt ground….if so will any ground wire work or do you suggest a dedicated ground wire directly to the house battery?

Thanks beforehand for your assistance.Whaler 220 Outrage



Hi Greg,

The best place to install a galvanic isolator is in the green wire between the ac shore power inlet and the ac panel. This will ensure that there are no alternate paths to dc ground thst can cause galvanic corrosion.

Cut the white jacking back on the shore power inlet where in the desired area. Cut the green wire and install the gi.

Hope this helps,


Easy to add AC?

Hi Guys,

I have a 26’ walkaround fishing boat and am thinking of getting an Easy Add AC shore power kit from your partner site, EzAcDc. It looks really slick and appears to be a complete shore power system for a great price.

I have a couple of questions for you since I have no experience with this type of install.

  • Does the system come with a reverse polarity feature for dockside?
  • From what I can tell it has just one master breaker. Is this breaker for all inlets? I will only be using a portable carry on 5,000 btu air conditioner and 22” TV
  • I have been told that I would need a galvanic isolator and bonding to prevent damage to metal parts on the boat?  The boat is dry rack stored
  • I have a Honda EU2000 generator and would like to know if it can used to plug in the shore power inlet.

Thanks.EzAcDc offers a complete shore power system for your boat wiring.



Hi Gregory,

All of the AC shore power systems on our sister boat wiring site include a reverse polarity indicator. In the event of reverse polarity, the red light will turn on. Since the panel only has a single, dual pole breaker that switches both the AC hot and neutral, this indicator is not really necessary, but we still install it in the panel.

There is a single, 20 amp main breaker on our panel. It protects all of the outlets including the remotes and rear units.

Galvanic corrosion only occurs when the boat is in the water. If your boat spends most of its life in the water or your marina has know wiring issues, I recommend adding a galvanic isolator.

Connecting your generator is easy. Add a plug similar to this Marinco unit on the end of your Honda power cord. It will simply plug into the new shore power inlet on the side of your boat.

Please let me know if you have any other questions,



Thanks for your prompt reply.

Do you think the 20 amp breaker will handle the Cruisair 5000 BTU Air Conditioner along with a TV?

As far as the galvanic isolator is this for protection only when shore power is used?



Hi Gregory,

I am not familiar with the 5k Cruisair, but the 6k unit only draws 11 amps max. The remaining 9 would be plenty for a tv, battery charger, and coffee pot.

The GI only provides corrosion protection when the boat is in the water and plugged into shore power.

Let me know if you have any other questions,


Add Galvanic Isolator to AC System?

Hi Kevin,

I’m very interested in buying one of the EzAcDc shore power kits for my boat, a Wellcraft Coastal 252 that I would like to add shore power to.

My question is about galvanic corrosion.

Do I need to install a galvanic isolator? If yes, where does it go in my boat wiring?EzAcDc offers a complete, easy to add shore power system for your boat



Hi Luis,

If your boat is in a marina where galvanic corrosion is an issue, you may want to seriously consider a galvanic isolator. The new, fail safe models like this one from Marinco are easy to install and very effective.

To add one of these to a shore power system from our partners at EzAcDc, you will need to cut the green grounding wire that runs between the shore power inlet and the shore power panel. It can go as close to the inlet or as close to the panel as you wish. Install 1/4″ ring terminals on the boat wiring ends that you created with the cut, and install the wires on the studs on the galvanic isolator.

Please let me know if you have any other questions,


Isolator vs Transformer


I’m in the process of adding shore power to the marine electrical setup on my welded aluminum Duckworth Offshore fishing boat.

Duckworth Offshore Based on earlier posts on your boat wiring sites, I am planning on adding a galvanic isolator. I am curious if should I use an isolation transformer instead?

I’m considering the Charles Iso-G2.

As always, thank you for your great help!


Hi Randy,

Isolation transformers work great!!! If cost, space, and weight are not an issue, I would certainly use the transformer over the galvanic isolator.

Send me some pictures when you are done,


Jon Boat Wiring


I am an engineer, but definitively not electrical.  If I look at wire, I get shocked.

I will try to be simple here.

I have a Jon boat, and the knucklehead before me has all of the boat wiring running to the battery. All of it. It’s so bad that I can’t even get the battery box lid on!Clean up the mess

But, that isn’t the worst part. He used no switches at all.  If you want to operate the bilge pump, find that bare wire and touch to the + terminal on the battery.

So, redoing the boat wiring is essential.  I would like ignition cables plus 2 wires (+ and -) to go to the battery.  I have looked at buses, fuse blocks, switches as well as switch panels to the point of total confusion, especially if you throw in the concept of a ground.

Which leads to the question, how the heck do you ground a boat? I mean specifically. Get this and put it there and attach to that, without which it is still a mystery.

Obviously, bilge pump, sonar, navigation lights, DC adapter socket, courtesy light, and livewell pump  all have their own amp draws.  Do I need to get a fuse block, insert the various amp fuses?  As for the switches, I suspect the + goes from the fuse block to the switch to the device.  Where does the – go?  To a bus with a lead back to the battery?  Where would a ground come in, since some instruments have ground connections?

Can you get a switch panel that does it all…with only the + and – from it to the battery?  Also, I have seen switch panels with 10 amp breakers rather than fuses….if my sonar has an inline 6 amp fuse, wouldn’t it be best to stay with there proper sizes (of course I would not remove the inline fuse unless I went with a block and used a 6 amp).

Obviously I need help. So any you can provide would certainly be appreciated.

Ron, P.E.

Hi Ron,

It sounds like you have a well engineered mess. I especially like that you need to “find the bare wire and touch to the + terminal” to make a device turn on.

My partners at EzAcDc have parts that should solve a lot of your problems. They have an eight switch marine electrical panel that includes a 12 volt outlet. It comes fully wired to control your navigation lights, bilge pump, courtesy lights, livewell pump, and provide power outputs for your sonar and other accessories.

The panel is built to plug directly into Ez’s 20′ boat wiring harness. This harness has one positive wire and one negative wire that connect to the battery. By using this harness, all other wires except your engine battery cables would be removed. It incorporates a ground block near the switch panel for future add ons.

Once plugged together, these two components will completely rewire the accessory system on your boat. If you need new components, Ez has navigation light kits, bilge pump kits, livewell pump kits, and even boat horns. All of these components simply plug together. A BS in electrical engineering is NOT a requirement to understand and install this system.

If you want to use your legacy parts, the harness includes adaptors to allow you to connect your old livewell pumps and navigation lights.

To connect additional DC components such as your sonar, Ez provides power cords off of the switch panel. They are protected by 5 amp circuit breakers. Each power cord has a ground, a constant power, and switched power wire (this is controlled by a switch of choice on the panel). I would recommend keeping your 6 amp in-line fuse with the sonar. If your sonar trips the 5 amp breaker, 10 amp breaker are included with the kit. Simply swap the 5 for a 10. Your sonar will still be protected by the 6 amp in-line fuse.

Hope this helps,

Kevin – future P.E.
(I missed getting my PE in Michigan by 2 questions. I plan to retake it in the near future.)