How to Calculate Clearance under a Bridge on a Tidal River

[@joreka2048]

Thank you for such an easy way of explaining it, love you videos man

[@tonywalker2372]

There's more to it than at first one would think, thank's for the tutorial.

[@lubberwalker]

Lovely clear explanation. In fact excellent. I have 3 notes. 1. You said you would, but didn't cover what happens when you get it wrong. It was like the last page of a whodunnit ripped out of the library book! The anticlimax was palpable. 2. I've been learning for so long, I can remember that airdraught used to be related to MHWS, at least that was what I was taught at the turn of the century. I have a handwritten scrawl of the imminent change, in my 5th edition reeds skippers's handbook (2007) ex Malcolm Pearson. 3. You say on a rising or falling tide... between these two depths. You then agreeably suggest that in reality you should go through nice and slowly. To join those dots, I would submit that ergo you don't really have the options of rising/falling, but just whichever of those equates to going against the stream. Particularly if said stream is springs and you're nearer the mid twelfths. This strategy has the biproduct of reducing the odds of meeting someone coming the other way at the bridge apex....just when you're uncontrollably rocketing through with no water over your rudder. 4. OK I said 3 notes but...in addition to the real life meteorological points you helpfully added... In my brain a bridge (generally) suggests a river. Rivers have a source of water volume and movement, related to rainfall on land, that's in addition to those of tide. It's worth noting these fluval factors exist and can considerably add to strength of stream firstly and secondly volume (height). So even the "stand" will be subject to this....turning it into an ebb of indeterminate strength and depth. In fact moving the expected stand to a different position up or down river. My brain is bleeding. Moral of the story. Don't do these calculations in the week after a storm or period of incessant rain. As in just don't trust air draught calcs in Britain.

[@davidshipkiss]

Nicely explained, thank you!

[@From_Refugee_To_Yacht_Owner]

I'm enjoying the videos. Much appreciated.

[@lubberwalker]

Wouldn't it be great if we had the reciprocal of a depth gauge up there, to let us know how close we shaved it?

[@lazalale]

Great video

[@edwardlongole1081]

Thank you very much!

[@thomasodea4120]

H.A.T isn’t changed for yearly fluctuations in tide hight .. so it’s not for the year as you as you are saying.

[@FreeSailingTutorials]

It's been a while since I recorded this video, so I can't tie your comment to the video. The values of Lowest Astronomical Tide (LAT) and Highest Astronomical Tide (HAT) are usually determined by inspection over a span of years. Springs and neaps vary and are, of course, detailed in the annual almanac.

[@tommooe4524]

Just check your depth and forget the mumbo jumbo

[@FreeSailingTutorials]

Good luck with that.