Hi,
I was wondering,, I have seen many pictures of harbours with what looks like a single gate lock. The most recent one is in Sunderland:
http://maps.google.co.uk/maps?hl=en-GB&ll=54.912531,-1.362173&spn=0.002094,0.005681&t=h&z=18
Now I was wondering, what purpose are these lock gates? Afterall, the tide will only be of equal height to that in the other area twice a day, and then not for very long, so a very fast passage would be required.
Many Thanks
TFM