1. I don't think that #1 is always, or even overwhelmingly commonly, the case. It depends upon the marina and situation. No one is using the outlet on my pedestal that I use but me. The same is true of the breaker for that outlet and the wiring in that immediately serves it. Unless I load it, no one is.
Right now I'm pretty good. It is all pretty new and clean. But, before they replaced it? It was crispy wire from 1980s with brittle ends, the back of the socket was corroded and melting, and the breaker was corroded. There was a ton of loss there -- as the heat demonstrated -- but it would never have showed up testing unloaded. Conditions at marinas vary.
As for the run from the marina distribution panel to my boat. It is probably 125ft. I dont know what the wire gauge is. That panel is outdoors, right near the saltwater, and not nearly airtight. I've seen inside. It is baked. Each breaker serves a few boats. Probably another boat on my breaker is pulling a load. But that isn't a guarantee. Some sailboats float off of solar and many boaters don't run AC when they aren't around. Very, very good chance of dock power float charging batteries nearby, but no guarantee.
Conditions in a newer marina are better. But, they are also more likely to have one boat per breaker in their panel, meaning that unless you are loading your run no one else is.
2) I'm not thinking so much about the cord as I am the connections. Here's an exercise for your. It is a game I like to play. Go to the marina on a beautiful hot summer Saturday when the docks are busy. As you wander down the dock chatting with neighbors, feel each cord right by the pedestal connection. How many are warm? How about darn right hot? Even on good looking cords? That's all loss before it gets to the boat not seen by testing at the pedestal. Many are quite the resistive heater.
Mine is spotlessly clean, relatively new, and in excellent condition. Same is true of the boat and pedestal end. I regularly run 25A on a 30A breaker. Yes. 83% load. Real world. My connection at the pedestal side is always warm.
You'd be right if you'd suggest that that degraded marina wiring aint good. But, it is what it is. And, it's real. Salt air, humid climate, rain, salty water dripping divers plugging in, people who don't hose off cords after cruising. Time. Gravity, vibration, people tripping or moving cords. It all dirties, loosens, corrodes and otherwise degrade these connections.
Now, think about the other side of that cord. Where it goes into the boat. Want to play a game? Bet many are just as warm-to-hot. And that boat that has an extension with a connection mid-way? Guess what I think it might be?
This is all real-world loss before it gets into the boat, never mind to the main panel, never mind to the AC.
Conditions vary a lot. But, if there is a problem, something is wrong. Assumptions are bad. Testing is good.
I regularly find drop when testing underload. Maybe it shouldn't be. But, I often do.
A 230v namplated HVAC that complies with the NEMA (Not NMEA) 10% recommendation is supposed to run down to 207v (230v - 23v). And even then degraded performance is allowed.
If we are seeing 208v open at the pedestal, that may reasonably likely be 206v under load at the pedestal, and 204v after a 1v loss on the shore power cord and a 1v loss at the connections. By the time it gets to the AC it might be 202v in many real world boats. That's far from the appliances nameplatted 230v and well below the absolute minimum 207v required of a recommendation-compliant 230v AC unit.
All of these little losses add up.
Everyone likes to expect that the appliances will be tolerant of everything "at least 10%" they say. But they like to neglect the tolerances allowed for electrical distribution which allows a lot of loss, up to 11% and sometimes up to 13% by the time it gets to the appliance.
Running AC units nameplated for 230v electricity off of nominal 208v is only guaranteed to work under relatively ideal conditions and, in the real world, basic operation is often hit-or-miss and accelerating wear-and-tear may well be a consistent miss.
I can't emphasize enough that I don't think one should ever really expect AC units nameplated for 230v to run on nominal 208v in the real world (which can be within spec and well less than 208v). Instead, I think one should be very pleased when it happens, even if it seems to be somewhat often.
Step up transformers are the consistent fix here. And they consistently work. And they consistently work because they solve exactly this problem. By intention and design.
That's my thinking at the least. Obviously opinions vary!
Instead, groups of slips share a breaker at the distribution panel.
