Newbie Bridge height calculation question

Mark26 said:
Hi, I’m in Penton Hook as well, with the same airdraft.
Cookham lock cut cut looks very tight to me from the helm, but we’ve never had a problem.
One day the lock keeper told me there was a good foot clearance, it looked more like an inch from where I was, but when he’s on the lock he has a clear and level line of sight.

After leaving the lock heading upstream, you will notice the river bank is lined with timber, normally the water level is a couple of inches below the timber. I always look at that, if there isn’t a couple of inches between the water and the bottom of the planks, then I am very cautious and would probably lower my mast.

A good thing to do with low bridges such as this and Windsor is to get someone else to take the helm and approach the bridge very slowly whilst you stand on the foredeck, or better still the front cabin roof, so you are looking back at the highest part of your boat as you pass under the bridge. If you are looking from the same level instead of looking up you will get a much better idea of how much clearance there is.
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Hi Mark, thanks for the advice...i am on H pontoon, hopefully down this weekend, if your about please drop over and say hi... always good to pick the brains of those more experienced than me :-)
 
A friend who had gone up the Thames a few years before we did, and kindly lent us some navigation books, said that they fixed a bamboo cane to the pulpit that was just taller than their air draft. Any bridges they were uncertain about they could approach dead slow and see if the cane cleared the bridge. If we had taken their advice we might not have had a close encounter with the Windsor Eton bridge! However that was due to bad helming and not watching that I was going under the centre of the arch.?
 
Grehan said:
On the Canal du Midi, Capestang bridge here is reckoned to be the most awkward because of it shape, although it's not the absolute lowest.
View attachment 111916
Approaching (on a de Groote)
View attachment 111917
Squeezing!
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You say it is not the absolute lowest, though all the guides I have read seem to say it is the minimum at 3.3. Have you done the canal? I am looking to do it this year, my solar arch is 3.5m, but I can easily remove the panels and a bit of the arch (by design to make it through the canals, which will get me to just under 3.3m. How many other bridges are there that are below 3.5m? Thanks for any info.
 
Leighb said:
A friend who had gone up the Thames a few years before we did, and kindly lent us some navigation books, said that they fixed a bamboo cane to the pulpit that was just taller than their air draft.
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Yes, that's standard practice and we also have a makeshift wind sock at the top, which is a useful reference when approaching bridge arches or lock entrances. The cane or pole doesn't necessarily take account of the width of (say) the wheelhouse, which can be significant even if below the absolute air height.
 
luckybeanz said:
You say it is not the absolute lowest, though all the guides I have read seem to say it is the minimum at 3.3. Have you done the canal? I am looking to do it this year, my solar arch is 3.5m, but I can easily remove the panels and a bit of the arch (by design to make it through the canals, which will get me to just under 3.3m. How many other bridges are there that are below 3.5m? Thanks for any info.
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Yes, done Capestang bridge and the Midi quite a few times (since 2004) and my comments stand. It's an awkward shape, with 'shoulders', but the absolute lowest are the two bridges at Carcassonne.
WATERWAY DEPTHS, HEIGHTS AND WIDTHS Practical Navigation //Waterway Depths, Heights and Widths
 
There may be another option for working out the bridges which is to use a laser red dot spirit level held or fixed horizontal at the highest point of the boat and see if the red dot hits the bridge.

Might be worth a play. Don't know how well it would work though.
 
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