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boat wiring

Old 12-21-2002, 04:03 PM
  #1  
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Default boat wiring

I have an 18' Mariah with a merc i/o. Last season I added a depth/fish finder and just picked up a raymarine 53 VHF radio. When spring comes I want to run the radio and F/F on a separate line to its own battery.
Is this is a sound idea. I am installing the second battery with a Perko switch. Any clues as to what gauge wire would work. And could I run the radio f/f on one wire to the battery? I am hoping to have those 2 items on its own switch from the dash, on its own circuit so I do not have to worry about drain.

Any thoughts are appreciated.

Mariah SX8
Merc 3.0
Jeep Cherokee
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Old 12-21-2002, 07:48 PM
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Default boat wiring

As simple as this is I don't even know where to begin. Clearly you've got something already wired up in there, because you've told us that you put the bottom machine in last year. I'm guessing that its a safe bet you simply ran the power wire directly to your existing battery and called it a day.
Not a real good way to set itup, but not the end of the world either.

OK, you plan on putting in a second battery. That's good. Get a second battery that is identical to the one you've got in there right now. Hook each of them up to your new battery switch (with a jumper cable between the two batterys negative sides. Connect your (+) cable from the engine to the output lug on the battery switch. Then connect the (-) cable from the engine to one of the battery's negative terminals (which will also connect it to the other battery because of the jumper. There, that takes care of your battery wireing.

Now, you have to run a line up to your consold. You now have a VHF radio and it will draw 5.8 amps when transmitting on high power (don't beleive me? Look in your manual). You didn't tell us what fish finder you have but it really doesn't matter, its going to be an LCD unit and they only draw about 1 amp. Just to make an honest man out of you we're going to assume that sometime you're going to get around to putting in a GPS too, so lets add another 1.0 amps to the mix for when it comes. So you have a total power draw comming up of 8 amps, but we're going to be very conservative on making up your rig and we're gong to call that 12 amps.

OK, you've got an 18' boat and I'm just going to say that your console is right in the middle, so it will take 9 feet of wire to get from rear to console, another 3 feet to get up to whatever the wire is going to be attached to, and then another 4 feet to wind around inside the boat to get to the battery switch. So, you have 16 feet of wire on the positive side and the same on the negative side (because you need to run a wire of the same size up to a buss bar you're going to buy and install inside your console as well. The chart for 3% power drop tells us that for a 32 foot run, 'cause that's what you've got, with a 12 amp draw you're going to need a 6 guage wire. It is going to amaze you how heavy a wire that is if you are not familiar with the sizes. Anyway, buy the the length of #6 wire you need, one length in black and one in red. You know what to do with them. Run the red one from the output lug on your battery switch up to whatever you are using for a distribution system, I'd suggest one of those small 5 breaker panels myself. Wire your stuff directly from it and be happy that you have a couple of extra slots in it for future expansion. Of course mount your buss bar a little bit away from the breaker panel and do not run the positive and negative wires right along side each other.

Nothing to it from here ....

Thom

"For every complex question, there's a simple answer. And it's wrong."
(--H. L. Mencken)
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Old 12-23-2002, 05:24 AM
  #3  
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Default boat wiring

Hey Thom, thanks for the reply,
My fault for not giving more info. I have runabout with a full dash set up on my boat, switches, panels, etc. I have an accessory switch that I am currently using for the fish finder. I wanted to use that switch to run a dedicated line for the radio and f/f. I ran the f/f to the accessory switch. I plan on use that switch or an extra switch for the radio. I am trying to make this as simple and correct as possible. But I was wondering if it was a good idea to have a 2nd battery just for these 2 items, or should I hook up the 2nd batter at the back of the boat and use the battery switch when fishing or resting.

My brother always says I make a simple job more difficult than it needs to be [img]/infopop/emoticons/icon_wink.gif[/img]

Thanks for the info you did provide.....

Brian

Mariah SX8
Merc 3.0
Jeep Cherokee
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Old 12-23-2002, 05:44 AM
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Default boat wiring

Brian,

Let me suggest this to you, don't run your radio (for sure) or your depth finder (your choice) off of a dash switch. Its just one more thing in the system that could fail on you (and switches fail frequently) and the radio is one thing that you want to keep working no matter what. So, avoid the switch and just tie into your fuse box or circuit breaker panel, whichever your boat has right now, and connect the power supply line to the radio to an open fuse holder and then fuse it as recommended by the radio manufacturer (and if you don't have anything from them telling you what to use just put in a 10 amp fuse). Do the same thing for the Fish finder and use a 5 amp fuse and you should be OK. If there are in-line fuses in the existing power supply line cut them out and throw them away. You only want one style or type of fuse used on your boat and you want them all in the same place - your fuse panel..

I know your intentions are good here but I want you to change your mindset by just a couple of degrees. You do indeed want a second battery, but the reason you want it is not to keep your electronics working for prolonged periods. The reason you want that second battery is to have backup power supply to start your engine should you have no, or insufficient, power from the first battery.

Thom

"For every complex question, there's a simple answer. And it's wrong."
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Old 12-23-2002, 05:49 AM
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Default boat wiring

Sounds good to me.

Thanks again for the info

Mariah SX8
Merc 3.0
Jeep Cherokee
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