We are a private yacht club and not a "public moorage" but have the same sorts of overhead to pay. Several years ago we did a breakout of costs per headwalk for power, because metering each 30-boat walk is as close as we can come to narrowing down boat power usage. We have about 30 boats per walk, and five headwalks.
To set the Scene: Here in Portland, Oregon, all boats normally winter in their slips, and long winter weeks of weather with regular precip and temps in the 30's to 40's are typical. About once per winter we get a two or three week period with continuous temps at about 20, full time.
Also, our headwalks are not uniform in power draw, as they are arranged by different sizes of boats. Bigger boats tend to use more power, we have found, historically. We harangue members about using any heater that would keep the interior above the 35 degree "freeze proof" point, but will always have a few that obstinately crank up their thermostat. (big sigh.)
FWIW, we have considered individual meters, but the meter and install cost is very high, and then we would need someone to read 'em all, and our all-volunteer club is often stretched thin as it is.
Our cost study allowed us to assign a rate-per-boat for each headwalk. It is averaged out for year-round billing, and we have the power budget figured out so that the member boats' power usage is not subsidized by the club, i.e. is revenue neutral.
Out of a total of $445. quarterly billig, my electricity "use" is $13.
If that all seems rather cheap... note that club work hours are required... and that I put in over 100 per year...
On the plus side, I get to operate our Dredge!
Loren