Dear Kevin,

I am currently beginning my first boat wiring project, a total rewire of a small Owens cruiser from the late ’60s.

Here’s my problem:

The old wiring runs behind the original paneling and headliner. I could try dismantling everything to remove and replace the wires, but am concerned about damaging any of the woodwork. It’s old. It’s gorgeous. It would be a bitch to replace.

I don’t mind leaving the old wiring in place and just running a new harness, but that still leaves the problem of installing the new wires without causing any damage.

Any ideas?

RP

Dear Ron,

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Kevin.

Hi,

I was given your email address by a friend who highly reccomended you.

I’m just about to rewire my boat as it’s winter. There are a few things that I would like to know before I start.

What would you suggest as to the thickness of cable from the battery to the 6 gang switch panel? I’m only running the normal things:

• Fishfinder
• VHF radio
• CD player
• Bilge pump
• Lights
• Horn.

I am also wondering if I should put an inline fuse in the live cable between the battery and switch panel and what size fuse?

Any other advice you could give me on boat wiring would be much appreciated.

Many thanks for your help

Paul

Hi Paul,

I am posting a handy spreadsheet that will help you calculate all of your boat wiring sizes.

Once you fill in the blue boxes for total wire length, the sheet will calculate the correct wire size needed for each wire run and for your main panel feed.

You will want to put a fuse or circuit breaker as close as possible to the battery. The size of this will be dictated by the total draw of your panel (Cell C20)

Emergency devices (nav lights, horn, VHF radio, bilge pumps, and blower) are typically wired for 3% voltage drop.

All other devices are usually 10%. Some stereos cannot tolerate 10% and you will need to run them at 3%.

Please let me know if you have any questions,

Kevin

Kevin,

With no generator or selector switch, my boat’s galvanic isolator is currently located between the shore power ground connection and the 110V ground bus. The 110V ground bus ties into the 12V negative bus and the boat ground (a steel pontoon).

I have recently restored my onboard generator and have installed a source selector switch (shore power or generator). I’ve read everything I can and I still can not identify to my satisfaction how to connect a galvanic isolator into an electrical system with shore power, an onboard generator, and a source selector switch.

The confusion (on my part) is that the battery selector switch being used has a separate connection for the ground wire from each source on what appears to be a solid bus bar connecting them. This suggests that both the shore power ground and the generator ground are connected and wired to the isolator inlet and the isolator outlet is wired to the 110V ground bus, the 12V negative bus, and the boat ground (steel pontoon).

Is this correct? Maybe the separate ground connections to the battery switch exist only to support the reverse polarity LED light, but it is still confusing.

Your guidance is requested.

Dave Freeman
Richland, WA

Dave,

The main reason for a galvanic isolator is to prevent stray current corrosion through your boat’s shore power connection. It basically induces enough of a voltage drop to prevent a galvanic cell from being created between your metal underwater gear that is electrically connected through your shore power ground wire to other metal gear in the same body of water – usually the dock.

To be effective, the galvanic isolator must break the shore power ground wire – the green wire between your inlet and your AC panel. All of the AC grounds on your boat wiring system should be connected together – Generator and existing AC systems.

You should have a single wire that connects the DC ground to your AC ground.

Hope this helps,

Kevin

Hi Kevin,

I am having A very strange problem on my 72′ Sunseeker that I can’t figure out.

I recentlly replaced all the overhead lights throughout the whole boat with L.E.D. lights. All of the lights are powered by 24 volts and are wired in series. I used 12 volt L.E.D.’s throughout the entire boat and they work fine.

I then started on the exterior of the boat, replaced all the lights on the arch, aft deck courtesy lights and the flybridge courtesy lights and they too worked fine. Ok enough of all that.

Here is my problem, The last lights I tried to replace were the port and starbord gunnels, I have nine lights on each side and they are controled by separate switches. I installed all my new lights and they work great for a couple of minutes and then they start flickering and then they stop, and then they start again.

This is driving me crazy!

Can you please give me some insight as to why this is happening ?

Thank You,

Keith

Keith,

Without looking at the system, I would guess that your flickering lights are being caused by a voltage drop problem.

The LEDs turn off when the voltage drops too low. As soon as the current draw goes away (the lights turn off), the voltage rises again and the lights turn back on. This causes in increase in current, a voltage drop in the wire, and the lights turn back off again.

Increasing the size of the boat wiring at least one AWG will probably solve your problem.

It sounds like you have a wonderful boat. Can you send me pictures of your project that I can post on the site?

Thanks,

Kevin