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Bridge heights

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JohnS
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Joined: June 1st, 2017, 6:55 am

Bridge heights

Post by JohnS » April 21st, 2019, 8:20 am

Hi all, does anyone know how often, if at all the bridge clearance boards are calibrated?
I’m well aware that there’s usually a few extra inches added on for contingency, which is good especially as some of the boards seem to lean over more each time I pass them. On the southern broads they appear to be more accurate. The reason I’m asking is I went under Beccles bridge last night, and I took extra precaution of taking screen down as it was going to be tight, when I went through I was shocked, it wasn’t just tight, there’s no way my screen would’ve gone under. So I have a suspicion the actual clearance at Beccles oldroad bridge may be lower than the board suggests 😳
I could be wrong of course, when it’s tight the bridge above your head always looks really close.
Anyway, I was just curious about calibration. I often see the rangers washing signs at Breydon but never see them measuring them, and never seen a ranger checking anywhere else.
I will bring my laser from work next weekend and double check the height of my boat.

Hylander
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Re: Bridge heights

Post by Hylander » April 22nd, 2019, 7:46 am

On a lighter note - it give new meaning to the word 'duck'. I have always been told that whatever the bridge height says it always errs on the side of caution and gives you a little bit more room , not less.

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Miles
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Re: Bridge heights

Post by Miles » April 22nd, 2019, 9:22 am

Not many Donalds on the Broads :D
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JohnS
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Re: Bridge heights

Post by JohnS » April 23rd, 2019, 11:04 pm

Hylander, I agree, certainly all the bridges on the northern side have a good few extra contingency inches, but slightly less so in my experience on the southern side where they seem to be more accurate. I've been through Beccles numerous times over the years and I have got a pretty good grasp of the height of my boat, all I can say for sure is, it was way tighter than previous trips under with the same guage reading. I'm just a bit concerned as to weather they ever get checked :? It's all well and good putting gauges at bridges, but surely they need to be checked every now and again? Maybe once a year should do, Or to at least check that the ones that are drooping to one side aren't actually on the move. The 3 gauges for Ludham bridge I saw in the winter all read different heights, they can't all be correct :lol:
Anyway, I got through so no harm done, I was just curious if anyone knew if anyone has ever seen them being checked.

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Miles
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Re: Bridge heights

Post by Miles » April 24th, 2019, 6:06 pm

Have you had any joy regarding this subject at all because it could explode into quite a big subject to handle?
I spoke to a chap years ago who reckoned he had dropped a weight of Postwick Bridge and that there was a huge disparity in his findings.
In fact I think he said there was way more room.
What about Potter?
Is it the apex or a horizontal line across inches below the keystone.
I'm addition, many have said that the Potter Bridge pilots height gauge states total different again. Maybe a bright physical line on the sides marking the actual true point of height may be better.
I know my boat could do 6.25 feet with the mast down but at Wroxham I just get through at the apex, so are the measurements spot on or not.
Any why is no pilot necessary for Wayford Bridge? I ask as it is a very low bridge.
Probably due to the lack of resources behind there.
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Vetchugger
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Re: Bridge heights

Post by Vetchugger » April 25th, 2019, 12:10 am

I think you have hit on part of the reason in your answer Miles. Its a question of beam as well as height especially at Potter. Martham Boats are not as wide as most hire cruisers and manage the bridge regularly. Wroxham is a bit more forgiving in the arch. Wayford Bridge is essentially "square" which makes passage, at the right air draft, relatively straight forward.

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