Low shore power voltage

That's been done, but those fuses would easily clear inspection.

Npt to say the marinas don't have a problem, but I think the main problem is on the boat. That's based on the only other boat that seems to have the problem is another old Hatteras and the marina manager's statement of having 208V while I'm only drawing 180V.

Yes the problem did occur at the other marina, worse. They did have a problem with their grid. However I suspect they appear to be not bad enough to affect most boats. I think we have an age related weakness that make us more suseptible. The boat next to us that's using the voltage booster is a '91 Hat I believe. At 22 y.o. it could easily suffer the same "weakness". Also, we have the problem whether on the port or stbd. shore power. So I suspect that the problem is further up line from the shore cords (although both could have a problem). Those fuses sound like the first place where the two sources meet. They're also the most likely place to take abuse from power surges and likely to have never been changed over the past 30 years if they didn't blow, hense the first main suspect.

You're talking about the on-deck S.P. conections. Haven't tried them. 50' of 50 amp is a lot for an old man to deal with on a transient boat when he can instead push a button. These S.P.s are on cablemasters and the feeds meet at a central location. So I would expect fuses at that point.
We have the electrical diagrams, but again, only on the boat 2 days. Will certainly avail myself of them when I'm able to check the system myself end to end.
BTW, after doing some reading I think you might have been in error when you wrote: "Doesn't it have an isolation transformer where you can adjust the input voltage with jumpers or moving terminal? Most hatt MY do". That doesn't seem to be to purpose of an isolation transformer. "Isolation transformer" seems to be another name for a galvonic isolator which grounds on the boat rather that using the shore ground. They can't be used to manually regulate voltage as far as I know. Relatively new knowledge for me however so don't hesitate to correct me if I'm wrong.

Seem to recall seeing it in the gen room (busy room with 2 gens, 4 a/c's, watermaker, etc.) Will check when I'm back on the boat, but I don't recall any adjustments.
"An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety. Isolation transformers provide galvanic isolation and are used to protect against electric shock, to suppress electrical noise in sensitive devices, or to transfer power between two circuits which must not be connected. Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass.
Suitably designed isolation transformers block interference caused by ground loops. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computers or laboratory instruments."

I'm familiar with the fuses you referenced, but we're using the Gendennings. So my place to start will be at the breaker box. I think I've probably gotten enough education to get me started on the troubleshooting. Thanks.

You may have missed this in post #5 "I asked the marina we're in now to check the accuracy and got a blank stare." So my plan is to get educated, and do some troubleshooting so I can at least point the "expert" in the right direction. Last time I had a marine electrician on board a boat we bought it had the anchor light instead of the masthead light hooked with the nav lights. He opened the helm panel and was planning to start cutting red wires (it was speghetti of red wires) until he found the right one. I had to suggest he go up on the mast and simply reverse the wires there. Experts aren't all they're cracked up to be. Just throwing money at problems on boats doesn't work. I've been sorely disappointed with the quality of yards (and "experts") in recent years.

I don't understand it either, but I expect to soon. I've found that (in almost all trades), that unless you can tell the experts exactly what the problem is and what the fix is you don't stand a prayer. So now, at this stage of my life, I have to learn another trade. Used to be you could tell your yard 'Here's the symptom' and they'd say 'Here's the solution. Your boat will be ready Monday'. Nowadays it's the blank stare and a month later nobody has even looked at it.

Yes, same problem on both port & stbd. SP so unlikely it's the cable. I think the most likely weekpoint is where they connect to the boat's grid. With luck it'll be a bad breaker, but I'll start tracing from there. Have to study a bit on the 3 phase issue mentioned earlier.

Marmot, you just gave the perfect illustration for my philosophy "Every man to his trade". My eyes literally crossed by the end of the first page of the first pdf.
On the second pdf, this stood out
"208Volt: 208 volts is a specific voltage (not derived from 240 volts) which may be supplied to a commercial facility
in addition or as an alternative to 240 volts. It is provided by the utility as 208 ±5% volts and should not be used
interchangeably with 220 thru 240 volts.
220Volt: Outdated and typically no longer supplied by utilities.
230Volt: Outdated and typically no longer supplied by utilities. However, 230 volts nominal may be referred to by
equipment design standards as this is the Nominal Utilization Voltage as defined by ANSI C84.1.
240Volt: 240 volts is a specific voltage which may be supplied to a commercial facility in addition or as an alternative to
208 volts. It is provided by the utility as 240 ±5% volts and should not be used interchangeably with 208 volts."

I believe I'm correct in thinking that a boat's electric is 240V, and this says 208V is a no-no for 240V. Yet this is two out of two with low voltage, this one stated as 208V. If I'm reading that right and this is as pevelent as it seems, a voltage booster should probably be on most boats. I wonder if that could cause me to get the low voltage. I believe the pdf said (+ or - 5%). If they're at 208V -5% that's 197.6V. Add in the draw from the other boats on the dock and it sounds like our 180V is accurate....and inadequate for our needs. Does that sound right to you?