A 50A/240V Charles transformer weighs 235Lb by it self. With IsoBoost, 245Lbs. They draw from the dock service so yes, I guess it could draw some current away from common line connects (like adding any other load) or until your shore service breaker trips.
The genset puts out 244 volts. The dock where this one boat is at reads 239 volts. When a dock/marina delivers less than 210 volts there are issues- not just with this boat but many boats. That's the issue being addressed with this thread.
239Vac is very good. No Wye transformer in use there. If the levels stay up there during the summer, then it's a great slip. Is that back at Sailfish Marina? If < 210Vac is an issue on other docks, you may never be happy at these places.
If you want to rectify the situation relatively inexpensively than remove your existing isolation transformer and replace with a buck -boost isolation transformer of the proper kva and if you have a larger budget and or the vessel will be travelling outside the continental U.S. than install a frequency converter and be done with it. Is the vessel running on 100 amp single phase now?
Ward's has a variety of solutions to this issue. Go see them or give them a call when you are in FL. http://www.wardsmarine.com/ http://www.wardsmarine.com/WARDS_EntireCatalog.pdf Alas, the Charles Iso-Boost is no more. I had a pair of those courtesy of the PO on my old Hatteras. Wonderful things.
Many marinas during peak summer months have the low voltage issue which is the reason for the thread. It's not specific for any one boat- but all boats that deal with low voltage.
One of the smaller dock owners south of here has the answer in fixing low power problems and people who complain; Docks are for storage, No live a boards alowed. Then kicks them out. The rest of the customers on the dock are happy when this happens. It's usually the guy running 4 A/Cs complaining and keeping the other boats from getting a good Vac level. And finally #10; Unplug the battle ships at the end of the docks. More juice for the rest of ya.