Just drive like the clappers and the wash of your boat will ensure that she stays exactly in the middle of the tunnel.
That was the advice I was given. Didn’t work. There seems to be a kink in the middle of the tunnel, or maybe that was my imagination. Your imagination does seem a bit overactive when you’re in the pitch dark surrounded by water.
Glad we fixed the problem with the headlamp; last time I drove through Islington Tunnel it was with three battery operated torches strapped to the front of the boat.
A few tips: open all your curtains and put all your lights on: then you can see the sides of the tunnel better and avoid bumping into them; make sure your headlamp is pointed upwards a bit so you don’t blind oncoming boats; and sing “What shall we do with the drunken sailor?” very loudly as you drive through the tunnel.