Originally Posted by oak
Boat at my home dock and voltage is ok
You need to check the voltage under load and specifically under the load of the AC when starting. Connect your meter (an analog meter will work best for this) and have someone start the unit. Look for a short term voltage drop. Do this at the power pedestal first and if you don't see a voltage drop, connect the meter to the power leads at the AC unit and repeat the test. If you now see a voltage drop, the problem is with the shorepower cord or connectors or the boat's wiring.
Since wire won't get smaller on it's own, the problem would be with one or more connections in the circuit.