ok, this sounds good.
If I drive upto Aber, and then boat across to Pwllheli, I'll only need to replenish fuel once at Pwllheli. By my reckonings (assuming reasonable weather!!), it's approx 30miles across from Aber to Pwllheli, which is probably just on or over an hr of travel time.... this is probably less than what it would be if I drove round
The only thing as you say, Ian, the 30mile crossing could be a bit dodgy if there's been some bad weather, or if there is some bad weather at the time. Although I trust the engine lots, I'd probably end up hugging the coast all the way around at which point I may as well drive anyway.
I'll look into this further at beginning of December