Good point about hiring, unfortunately (or maybe fortunately?) I have my own, so I know I need 8' 4" or 7' 4" depending on whether canopy is up or down. I do now accept it's not possible to get accurate values in advance of arrival, but RS2021's post and the concept of % chance is quite interesting. If I know published bridge height, and the current river level below the next and previous high tide levels, I ought to be able to guesstimate current clearance on an *average* tide. That doesn't give me % chance of course, and all other factors (wind, pressure, rain, etc) notwithstanding, if it's a matter of a few inches either side of clearance on a descending tide I might be inclined to chance it. And the further away from my required clearance the guesstimate is the less chance I have of a successful transit. An exercise to try for next time perhaps.