It seemed OK in the Ham tunnel until the roof arch became rocky and very uneven. Then I watched the port & starboard nav lights get very close to the lumps of rock sticking out, but actually we didn't touch at all.

The tunnel was smooth brick for a distance at each end but rocky in the mid section. The 600 metres seemed to take forever.

It was a relief to exit to the top lock and then onto the wide open river Meuse again.