[ChristinaM]

The average difference is 8" but with tides it can be up to 12' and it changes constantly. It'd be really tough for the ships to handle in the confined space especially when eddies form along the edges and with currents changing over a period of hours. A lot of these ships only travel at 10-15 knots and they aren't very maneuverable.

I was recently on a sailboat going through Hell Gate on the East River in NYC. It has about a 6' tidal range. We can motor at 6 knots. When the tide was at peak flood into Long Island Sound we were doing about 1/2 knot over the ground. You can time an East River transit to work around the tides, the Panama Canal is too long for that to work.

(I don't recommend transiting Hell Gate under those conditions, the UN closed the river longer than they said they would and we only managed because there wasn't any wind. We should have anchored and waited a few hours, we would have gotten through almost as quickly.)