Watermakers by boat length.
Length is a useful proxy for the two things that actually decide the choice: how many people are aboard, and what electrical system the boat has to make water with. Each band below starts from a realistic daily figure and shortlists what fits.
Small-boat watermakers: what fits a 12 V bank and a locker, sized against two people at 30 litres a day, ranked by watt-hours per litre.
The most common cruising size in Australia. What fits a 12 V bank on a 33 to 40 foot boat, sized against three aboard at 66 litres a day.
The band where every option is open: 12 V, 24 V and mains all become practical. Sized against four aboard at 100 litres a day.
Larger cruising boats and charter catamarans: 24 V banks, usually a genset, and five aboard at 140 litres a day.
Large cruising and charter vessels: 24 or 48 V, a genset as standard, and six aboard at 180 litres a day.
Superyacht and commercial scale: mains power, high output, eight aboard at 280 litres a day and guests who do not ration.
By what kind of boat it is
Why length and not model. A boat’s length tells you roughly how many people are aboard and what voltage the house bank runs at, and those two things narrow the choice more than the badge on the transom does. Where we can put real tank and battery figures behind a specific model, that page will say so and show them; until then, a length band is the honest level of precision.