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.

Hello,

If a European built boat comes to the United States, what is the best way to connect to shore power, i.e., 24/240V Euro to 12/120V American?

Thank you,

Warren

Warren,

If all of your AC appliances are designed for 50/60 Hz operation, then you can solve this with a Step UP transformer that will take the American 120v and up it to 240v.

You will need to research the AC components on your boat to answer this best.

The only connection between your 24v system and shore power is the battery charger. If your charger can handle 50/60 hz, then the Step UP transformer will work for this also.

Hope this helps,

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

Hello,

Please could you comment on the boat wiring diagram that I’ve drawn up.

It includes:

• Twin Verado outboards
• Shorepower
• Generator
• House batteries.

I’m currently trying to wire up a new boat here in Oman (no technical expertise available) and I’m really concerned about dangerous AC currents floating around the boat whilst my family swims.

Please could you have a look and give me your comments as I’m no expert at this?

I know that I’m missing an earth wire from the fused junction!

Any input from yourself will be most welcome.

Kind regards

Glyn

Hi Glyn,

Very nice diagram!

I have a few comments.

• Add circuit protection at the source of power for your 24 hour emergency bilge pumps fuse panel.
• Add circuit protection at the battery switch for your main DC distribution panel
• Your shore power ground (green) needs to run to your AC ground buss
• Your galvanic isolator is connected between your shore power inlet and the AC ground buss in the green wire

Also, I would consider not connecting the 3 bank inverter to all 3 banks. Instead,

1. Connect two legs to the house battery bank
2. Connect one leg to the port engine battery bank
3. Connect 0 legs to the starboard engine battery bank

This would allow you to completely drain your dc system with the inverter and still be able to start your starboard engine and charge the system through your automatic charge relay

As drawn, your boat’s AC electrical system should be shock proof.

Most marine AC problems occur when the DC ground is not connected to the AC ground. If you boat has an AC fault to a DC component, the common ground will allow the circuit protection on your AC distribution panel to trip and not energize the water below.

Please send me pictures of this project,

Kevin

Hello Kevin,

Thanks for your input.  I’ve updated the pdf (in case you want to use it)

I’ll take pics and send them to you. But, it might take a while as I’m in Oman and it’s a real struggle to source the various electrical components. Nevermind the marine grade wiring (at the local marina they have a bad habit of using domestic grade wiring).

That’s why I’ve elected to attempt all this myself.

Regards

Glyn