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BigCatOne 05-21-2007 04:14 PM

12v system and 24v system on 1 boat at same time?
I am building a sailing catamaran which I intend to power with two Yanmar 6BY260 engines, which come with only a 12 volt systems. These engines are the new type 2 low emission engines which use computers to reduce fuel consumption and pollution. I want to run a 24 volt boat, and my question is, has anybody ever run a boat with two different dc voltage systems? I would just add a 24 volt alternator to each engine, and set up separate systems for 12 and 24 volts.

I can't find any reference to this idea anywhere. Everybody seems to go with a 12 volt system and a 120 or 240 AC system. I have no desire for an AC system, even though everyone else seems to want one on any boat bigger than a daysailer these days. Can/should a 12 volt system and a 24 volt system share a ground? Are there any other issues I should be concerned about?


Tim Dunn
Arlington WA

Idiens 05-21-2007 04:33 PM

Quite a lot of stink-pots use both 24V and 12V systems. So I don't think it's unusual.

sailingdog 05-21-2007 05:27 PM

A lot of stinkpots use two DC systems as some of the bigger engines use 36 or 48 VDC for starting their very large engines... :D

My questions is "Why do you want to run both 12 and 24 VDC?" It seems like you're just going to complicate your life doing that.... Unless you have a specific need, it would seem to be a much better idea to me to keep the boat as simple as possible.

Also, you don't say where you are located... but in the US, the number of 24 VDC accessories isn't all that high, since 24 VDC systems are more common in other parts of the world AFAIK.

BTW, another multihull sailor is always welcome to sailnet. :D BTW, what design is the cat going to be and what construction method are you using to build it?

Giulietta 05-21-2007 05:52 PM

To me...makes absolutely no sense...

BigCatOne 05-21-2007 06:31 PM

24 volts are better than 12 volts because...
24 volt is better than 12 volts, because the wiring is cheaper and you don't spend as much money heating wires. These engines have onboard computers and electronic injection. The engines use 12 volts to run, and won't run without it. I consider this the simplest approach, actually. I would make the whole boat 24 volt, if only the engines came with a 24 volt option.

And, I am having no trouble finding 24volt gear, except for 2 or 3 low draw electronic items, which I will power with a DC to DC converter, which costs about $85.

As far as I am concerned, 12 volt systems are an obsolete relic of the days when boats had much, much less electrical gear. Just price the cables to run a big electric anchor windlass with 12 volts versus 24 volts, and you will see my point. I'd go with manual, but this is a 65' boat we are talking about, and it will operate in coral waters, where a rope-chain rode isn't a practical option.

And, if it so common to do this, why can't I find one lousy wiring diagram for the idea?

I am designing my own boat, as I have been an amateur designer since the days of planimeters, splines, and French curves. I had a bad experience in 1971 sailing from Hawaii to Seattle, and decided to learn yacht design in self-defense. The construction method will be modified Kelsall, with a radius chine design. The radius chine will have a 2' diameter throughout, hand laid up, with the rest of the boat made by resin infusion on a flat table.

erps 05-21-2007 07:55 PM

Look up the wiring for a series/parallel switch used on big rigs (trucks). 12 volts to run all the trucks accessories except the starter, which is 24 volt and activated by a solenoid that changes two banks paralleled to series (and it doesn't mess up the rest of the system)

oldboatnut 07-22-2016 04:59 AM

Re: 12v system and 24v system on 1 boat at same time?
It is essential that the 12v negative and 24V negative are connected together. I have both on my boat mainly as I need 24v to start a large diesel its is also useful for 3500 lb windlass. 12 v gear is standard and easier to get , replace and service in most parts of the world, you could ring main in large cable say 35 or 50mm and then do short localised runs with a breaker where required. Old welders often have lengthy cables usually tinned copper of large diameter that can be picked up for cents in the dollar.

JimsCAL 07-22-2016 07:51 AM

Re: 12v system and 24v system on 1 boat at same time?
And a 9 year old thread rises from the ashes.

capta 07-22-2016 09:40 AM

Re: 12v system and 24v system on 1 boat at same time?
In the days of 32 volt marine systems it was quite common to have some things (like the gauges) run on 12 volts. Chris Craft did this, for one. It was a total headache and there were always problems determining which wires were which system.
Whatever you think you will save in 'cheaper' wire you will spend 10 times over on 24 volt equipment. The KISS principle will save your sanity and many, many hours of frustration and maintenance, never mind having to special order 24 volt equipment from a far off anchorage, if you plan to go cruising.

RobGallagher 07-22-2016 10:16 AM

Re: 12v system and 24v system on 1 boat at same time?

Originally Posted by JimsCAL (Post 3589457)
And a 9 year old thread rises from the ashes.

I call them "Happy Easter" threads.

Nothing like a good resurrection to get the party started.

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