24 volt boat electrical systems are on most commercial vessels, such as trawlers and work boats who use 24 volts as a standard system voltage. There are larger sailing yachts, trawler yachts and power boats that also have 24 volt electrical systems. In fact, so do many commercial vehicles such as trucks and buses.
I have always been perplexed by the relatively low use and acceptance of 24 volts in so many pleasure boats given the significant advantages that it offers. You can get deck winches and windlasses in 24 volts, and trolling motors also come in 24 volts. Also bow thrusters come in 24 volts as do furling systems or hydraulically powered systems as well. If you use inverters to power up AC appliances then also 24 volts is available. In addition you can get toilet waste pumps, water pumps and even lighting is available in 24 volts.
It is derived by connecting 2 x 12 volt or 4 x 6 volt batteries in series. The usual reasons quoted for not installing 24 volts in boat electrical systems are the difficulty in obtaining appliances, lights, electronics etc. This argument is basically flawed as most equipment and lights are also available in 24 volt ratings, and what few things that are unavailable can be supplied by a DC-DC converter. Much electronics is also able to function on 12 or 24 volts. The nominal charging voltage for a 24 volt battery system is 28 volts to properly charge the battery bank. One drawback is few engine manufacturers configure diesel engines in 24 volts, at least around the 30 hp or less, and optional as engines get larger.
The disadvantages of 24 volt boat electrical systems are very few with a very slightly higher rate of system leakage problems in damp atmospheres and that in poorly maintained equipment. The big advantages of 24 volt boat electrical systems are significantly reduced cable sizes, by 50% as the current is halved. On long cable runs this reduces voltage drop problems, and on systems such as a windlass then it means big reductions but for lighting not so much.
It should be noted that there is a practical minimum size for general cables and wiring in boat electrical systems. So many get bogged down in working out allowable voltage drops and sizing cables to the minimum they can.
In practice I wire boats with a minimum of 1.0 mm and standardize
at 1.5 mm, whilst you check power consumption and voltage drops in the end it is
more than capable of carrying loads. Even houses use a couple of standardized
wire sizes, and limit the connected loads. Equipment size and weight is also
reduced with motors being much smaller, and more efficient. Consequentially other weight savings can be
realized as smaller battery banks can also be used, so weight savings on boat elec trical systems heavy
cabling and battery banks. There are also reductions in the level of
system disturbances but that is dependent on the equipment used.
Is it economical to change over from 12 to 24 volts? probably not. But should you be deciding on building a new boat then absolutely I think going with a 24 volt boat electrical system is a great idea. When coupled with new battery technologies such as Lithium Iron it makes sense. You can get everything in 24 volts, and if some electronics are not available except in 12 volt a DC to DC converter will solve that.
The decision is about what type of boat and even how big a boat. While much is discussed about reducing cable sizes and so weight and some expense, in the scale of things these are not that great. But system efficiencies make the equation work. Given recent developments I would now seriously look at 48 volts boat electrical systems on any reasonable sized boats from say 40 foot and upwards. More about that in the 48 volt discussion. Look at your boat electrical systems and all about boat electrics.