Also checked out the air and fuel pressures. Seems OK.
Bonkers really. I drove an hour each way to plug in the computer, give the boat a hose down, check the air and fuel pressures (and flush the motor at the same time), change the gauges and change the gearbox oil. So 1.5 hours working on it for 2 hours of travel.
But needs must. Still, it meant I left home at 4:30 and was still home in time for tea.