Isolation Transformer

You have an internal ground fault problem, you need to fix the problem and not cover it up with an IT.

Indeed, fix the problem don’t cover it up. Most of these issues are caused by an appliance or inverter which has N and G connected together

I can assure you that there's a 95% chance that the problem is with your boat. Very rarely is it the marina.
You need a qualified MARINE electrician to find the fault, not a residential guy.

Something not mentioned and not discussed much because it is a sad subject;
If you have a grounding issue, this IS a safety issue and should not be swept under a rug (transformer).
You still have a potential safety issue.
Find it, fix it and sleep well...

I did an overhaul on the AC system aboard my 1966 Hatteras. We combined the twin 30a inlets into a single 50a. All new panels and breakers. We added a Hubbel isolation transformer. I use a portable voltage booster (from Ward's in FLL) deployed as needed. An isolation transformer with built in "smart boost" would be nice, but they are quite pricey.

There is not much that needs a boost from a proper dock electric service.
AND, Nothing is free. You want Volts, that takes Amps.

W/A =V will not bend.

I am concerned that you have been reading that drool from das other web site. Just because a few folk agree on a rumor, does not make it correct.
Here we have techs and engineers.
We also know the rules and how things really work.
And of course my favorite, OHMs law. (Post #10)
https://en.wikipedia.org/wiki/Ohm's_law


Corroded connections on the dock will result in low loaded volts. A bad connection will get hotter as more current is pulled thru it.
As it gets hotter, voltage goes lower, resistance increases, more current tries to flow thru to answer the wattage/load.

A long dock with you on the far end will emulate a bad connect also.
That long cable run will get warm and turn into a long (long) resistor as above also.

Adding a boost transformer, will draw even more current thru the bad connection (or long cable) to generate a taller voltage. (Post #10).
At some time, something will burn up. Either that bad connect or an option during under wattage.

The interesting thought, this will not generate a GFI issue. Any (fault) current on the green wire causes this.
Fault current is from your boat.

Are these supposed qualified sparkies looking for fault current OR low ACv issues?
These are two different issues.


Further things to consider.

Many folk are freaking out over 208Vac service.
Later marinas are using 3 phase commercial service to the docks. A Wye transformer reduces this service to usable 30 & 50 Amp services.
There is nothing wrong with 208Vac. It does provide plenty of current and answers the Wattage requirements well.
Some Air units may show a low power alarm, easily corrected in the panels set-up options.
The use of a boost transformer here may reduce the available current to the wattage/load. (Post #10).

Early, real early dock service GFI breakers were later deemed to sensitive.
Later GFI service breakers were designed just a bit less sensitive and reduced many nuisance trips.
If your having intermittent GFI dock service pops, maybe investigate the specs and data codes on the suspect breaker.

Are you having any under water current leaks?
Here lies the answer to a qualified marine sparkie.

look, it’s not rocket science. Physically disconnect every non marine appliance (stove, washer/dryer, fridge, freezer, ice maker etc. that means not just pull the breaker which will not disconnect the N, but physically pull the plug or cut the hard wired wires. Re connect them one by one till it trips.

Recommend you get this figured out or use an IT as a last resort. Reason being is more and more marinas are installing the GFI's. In fact, it is now code in nearly all areas so any time a marina does any changes or retrofits they are required to come up to current code which is GFI's.

You may have spend a lot of money but you don’t know whether these “professionals” did it right. Did they physically disconnect all your appliances and reconnect them one by one? Washer. Drier. Stove. Oven. Fridge. Ice maker(s). Freezer. Dehumidifier. Water heater.

do you have a non marine inverter?

is the generator (which bonds N to G) connected with a switch which disconnects the N when using shore power?

have they checked that there isn’t a connection inside the panel between the G and N busses

all easy things to check and 99% chance the problem is one of the above

The inverter is critical. Marine inverters have relays that only bond N to G when in inverter mode. RV or off the grid inverter bond N to G at all times and will trip GFCIs