Nibj - Thanks for sharing the rest of the story that it wasn't just an arbitrary restriction imposed by the charter company.

I think the majority of marine AC units are Dometic Cruisair. Are you getting an error code on the control panel when the unit shuts down?

Common codes are:
- LO / AC (low voltage. Typically overloaded AC generator or poor dockside power)
- HI / PS (high pressure. Typically loss of water flow from clogged strainer or AC pump failure)
- HP / -- (high-pressure switch failed to open or circuit wires open)
- LO / PS (suction pressure too low. Typically loss of gas)
- LO / -- (suction pressure too low. Failed low-pressure switch or circuit wires open)

Prior to the unit shutting down, I would visually confirm that there is a strong, steady stream of seawater coming from the AC outlet. If not, I would go through this order of checks:
- Confirm the thru-hull is open 100%.
- Check for clogged external sea strainer near the bottom of the hull (typically from sargasso or plastic bag).
- Check internal sea strainer for obstructions. You'll need to close the seacock and then open the strainer cover to check the strainer basket.
- If intakes are clear, then there could be air pocket entrapped in the seawater line. You'll need to bleed the air of the system. On my boat, I open the seacock, activate the AC unit so that the pump turns on, carefully loosen the seawater strainer cover to allow some seawater (and air) to squirt out and then tighten the cover.

If you have good flow, then perhaps you have a voltage issue. Have you tried shutting down the opposite hull AC unit to see if this prevents the AC from tripping? On many boats, the generator is minimally sized with little excess capacity to simultaneously power much besides the AC units. Even the start-up currents of other appliances might cause a low voltage trip of an AC unit even if the generator is still able to run. You've presumably already confirmed that no one is using high amperage appliances while the AC is running (such as microwave, blender, portable hairdryers). I was on a charter boat where the AC or generator would routinely trip offline each evening around 5 pm (as the crew were showering). After a couple days, I had two female crewmembers come up from their respective cabins to complain that both their 1500W hairdryers always seemed to stop working at the same time.

Another culprit can be icing of the evaporator coil. This can happen if the unit's cooling operation runs too long on a warm humid day. For example, if the thermostat is set unrealistically low (e.g. 65 deg-F), if cabin hatches and doors are left open, or the AC outlet air vent is blocked (by shoes/bags/linens/etc).

Hopes this helps.