12 to 24 volts

[DownWest]

If fitting the bowthruster, as required by SWMBO, an extra 12v battery up front would negate hefty cables from your aft mounted batterys. The charging cables would be relatively small in section.
I think you questions about 12 v 24 have been answered. Recreational boats moved up from crude small engines to modern diesels, and for cost reasons used car sources, i.e. 12v.
Q E D
A

 

[eidiohir]

If fitting the bowthruster, as required by SWMBO, an extra 12v battery up front would negate hefty cables from your aft mounted batterys. The charging cables would be relatively small in section.
I think you questions about 12 v 24 have been answered. Recreational boats moved up from crude small engines to modern diesels, and for cost reasons used car sources, i.e. 12v.
Q E D
A

The point is 12 is better than 24 whatever about running heavy cables.Please read my posts.
QED indeed

 

[mattw]

As others have said the 12v standard appears to have come from the Auto industry. A lot of yacht engines are converted car engines so they will have come with 12v systems. Replacing them with 24v systems would have involved much expense for not much gain. I have read somewhere that there is interest in moving to 48v for cars, so maybe we'll see that happening in yachts at some point.

On a related note low voltage lamps tend to be more durable as they have thicker wire elements than their higher voltage counterparts. For low power navigation lights this may be a problem. It is not an issue for LED lighting though.

 

[DownWest]

The point is 12 is better than 24 whatever about running heavy cables.Please read my posts.
QED indeed

I agree that 24v is better, my post was about the easiest solution in your case.
A

In the boat I was talking about (70ft). The 12v runs were very short, as the start batteries were right next to the engines. All the rest was 24v, more efficient. The hot water was 240v off the genset. At 12v, that would be 250amp. (3kw heater)