I made the mast to fit under the bridge and left 1cm to spare but was really expecting they left a few cm as well to allow for wakes from passing boats,etc. The bridge is fairly new, like about 2 years old and was supposed to have 5.2m clearance at HAT which will be in 2 months time when high tide is another 22cm higher then today's high tide. I touched the bridge about 10cm before high tide so that's over 30cm clearance that I should have had. Also the 5.19 is for empty boat, with today's 300kg load it would have been more like 5.12 m
With no boats around and no wake I should have had about 40cm clearance but instead I was out by probably 20cm or so, all up the bridge height must be at least half a meter out from charts . I noticed the've recently changed the height of the bridge next to it from 6.6m to 6.1m after 35 years in operation, although is still displayed as 6.6m on charts, so maybe they are both sinking.
A laser measurer would only work right under the lowest part of the bridge so I'd have to be able to get right under the bridge first , so mast has to stay home or use a kayak. Easier to just cut another 20cm from the mast, move the spider and shorten the stays then have another go. Still, its disappointing when you can no longer rely on officially posted bridge heights.
"You could heel your yacht" - I could if was a beach cat but mine is too heavy to fly a hull. I could gain another 30cm if I flood the hulls up to cockpit floor then release the water once I got on the other side of the bridge. Just need to relocate the batteries to higher ground.