Selecting wire dimensions for an existing system

[Frederik283]

Hi all!

I'm in the process of going over my new (to me) boat's electical system and have a question I hope you can help me with.

The cables from the top of the mast are currently fed through a hole in the deck without any waterproofing around the hole. I would like to replace these holes with some electrical deck plugs.

My problem lies in determining the required amps for these plugs.

The cables are:
- VHF
- Lights
- Wind instrument

How would I go about measuring the requirements for these deck plugs?

[Sailmonkey]

The vhf will be a pl-259 so-239 bulkhead connection, no need to measure current.

The lights will just need a plug that is sized to match the amps city of the wire

The wind instrument is milliamperes

Best bet is to look for appropriate waterproof ness

[Dsanduril]

The VHF is presumably the antenna cable, so no Amps, you'll need a coaxial connector.

Wind instruments so low you won't be able to measure them.

Lights, do you have an ammeter on your electrical panel? Turn on the lights one by one and see how much it changes. Running lights are likely a couple of Amps at most (if incandescent), steaming and deck/spreader lights could be more, but probably less than 10A.

Having said all that, a connector near the mast can make mast work easier, but connectors on deck IME get grotty and corroded pretty quickly regardless of quality and waterproof-ness. I'd suggest putting a gooseneck at your deck entry to keep out water, and putting any connectors just below deck. Gooseneck sized to permit passage of the largest connector you need along with all the wires.

Just my 2 cents, YMMV.

[Brian.D]

Since you did not specify how many lights, height of the mast, or even a type of boat so we can look up the specs on the boat we have to divert you to do your own research.

The ABYC dictates (your choice to follow or not) wire size based on current load and length. There is a chart at Blue Sea that will help you.

Now, if you really need assistance I would recommend telling us how many lights you have on/at the top of the mast. Most will have three/four or a combination light. Steaming Light, Anchor light, Port light, Starboard light, Stern light. Some of these could be on the hull or pulpit/pushpit. So we need to know.

We also need to know how high is your mast? That will help.

However, If you want to just rerun the wiring, 14awg or 12awg will work. Maybe 16awg, but I would go minimal 14awg.

JMHO

[Frederik283]

Thanks all for your insight, much appreciated!

I think I might go with a gooseneck as suggested.

Would I be able to measure the amp requirements using a multimeter on the amp setting for the lights and wind instruments by measuring the positive and negative wires at the base of the mast or is this not precise enough?

The boat is a Willing 31 with a 10 meter mast. I have a deck light and a white navigation light up top.

[GordMay]

To calculate Amperage, divide the total lamp wattage, by the applied voltage.
To calculate wire size see:
“Ohm’s Law & Boats” ➥ https://www.cruisersforum.com/forums....html#post1256

Chart ➥ https://www.cruisersforum.com/galler...r&imageuser=79

Chart explanation ➥ https://www.cruisersforum.com/gallery/showimage.php?i=1322&catid=member&imageuser=7

[Frederik283]

Fantastic Gord!

How would I measure the wattage?

[GordMay]

Originally Posted by Frederik283

How would I measure the wattage?

The wattage will be listed on each lamp, or specified on the fixture data sheet.

[Frederik283]

I'm gonna have a look at the mast lights today then while it is still in the shed. If there is no wattage specified on the lights is there any way to measure it myself?

[AiniA]

If the masthead lights are not LED it might be a good opportunity to convert. This will dramatically reduce the size of wire you need.

[Bill O]

If they are still incandescent bulbs, would consider changing them out for LED (especially since you have your mast down now).

Much lower wattage and sometimes brighter than incandescent.

[Sailmonkey]

Unless you’re you’re specifically looking for connectors rated in milliamperes I believe you’re massively overthinking this.

[Dsanduril]

Originally Posted by Frederik283

Thanks all for your insight, much appreciated!

I think I might go with a gooseneck as suggested.

Would I be able to measure the amp requirements using a multimeter on the amp setting for the lights and wind instruments by measuring the positive and negative wires at the base of the mast or is this not precise enough?

The boat is a Willing 31 with a 10 meter mast. I have a deck light and a white navigation light up top.

Absolutely can be done with a pretty simple meter. If the mast is down and they are incandescent bulbs (and you don't want to change them as described above) you could probably get pretty close just by measuring the resistance using your meter. E/R=I, if you use 14V as E (for charging) you will get the worst case scenario. That way you don't even have to provide power to measure the current the lights will use. Your estimate will be high, as the bulbs heat up in use the resistance goes up and the current goes down.

Most multimeters only go to about 10A, which should be fine for both lights, but if you want to measure current directly I would estimate it as above first to make sure you won't exceed that. Then power up the lights with the meter in series on the A setting.

Originally Posted by Sailmonkey

Unless you’re you’re specifically looking for connectors rated in milliamperes I believe you’re massively overthinking this.

+1. None of these are big power users, even in incandescent style. At most 10A for the deck light, more likely 3-5A. Everything else is small potatoes. If you anchor out overnight a lot your batteries will thank you each morning for switching to LED. Even though is probably only uses 1-2A that can add up overnight. For the deck light, to me that is less critical, but I probably average less than 5 minutes/night using the deck light, and even in anger never more than 30 minutes at a time. If it is something you will leave on a lot then I would consider LED.

If they're both rarely used then probably not worth the $. Since these are rarely disconnected, we just use a terminal strip under the deck near the base of the mast. That way you don't have to worry about connectors, corrosion, capacity (pretty hard to find a terminal strip that is not rated 15A or greater). Also much easier to install than connectors, and easier to feed each wire in/out of a gooseneck than with bulkier connectors.

[Adelie]

Don’t install waterproof connectors install outlets thru the deck like this:

https://www.thegpsstore.com/Shakespe...let-P2147.aspx

Especially for the VHF coax, lot of losses at connections. Even if there isn’t much initially as the connector ages it will become more lossy.

[Discovery 15797]

I agree with Sailmonkey...you're massively overthinking this.

Most likely you currently have 14 gauge or maybe 16 gauge wires for your lights.

As previously stated you will want a SO-239 bulkhead connector for your vhf antenna. Don't cheap out on the connector. Also, use something like Coax-Seal and silicone tape on the deck side of the UHF connector to prevent water from getting inside the cable and connector.

The next question is how many wires total do you have coming down your mast?

You'll probably want a connector like this. You can get these types of connectors with more pins...up to about 24 that will handle 10 amps.