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Air draft on Grand Union


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Just now, perfectlydressed said:

Hi can anyone tell me what the air draft is on the Grand Union for certain please?

 

No we can't because, as has been said, so often, it depends upon the profile of your boat. A narrowboat can have a higher air draft than a wide boat. Many bridges and tunnels are arches, so the air draft right at the side may only be a very few feet, but in the centre perhaps 10 feet or more.

 

The fact that you are asking this strongly suggest the boat may well be too wide and too tall.

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Quoted numbers are:

 

Brentford - Berkhamsted 8' 2" (2.49m)

Berkhamsted - Braunston 7' 10" (2.38m)

Braunston - Camp Hill 6'6" (1.98m).

 

However I endorse the remarks that it depends on width and profile of your roof.

Given how old the figures I have quoted are, I suspect they may b valid only for a narrow beam craft - a wide beam of those heights may well find places where they could not get through.

 

Where do you want to get from and to, please?

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26 minutes ago, perfectlydressed said:

Hi can anyone tell me what the air draft is on the Grand Union for certain please?

 

22 minutes ago, Tony Brooks said:

No we can't because, as has been said, so often, it depends upon the profile of your boat. A narrowboat can have a higher air draft than a wide boat

 

 

Here is why

The blue line shows the maximum air draft allowable for a Narrowboat, and the Yelow line shows the maximum allowable air draft for a fat-boat.

 

 

 

Arched Bridge and Widebeams.jpg

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53 minutes ago, perfectlydressed said:

Hi can anyone tell me what the air draft is on the Grand Union for certain please?

As others have said, depends on the cabin profile

 

39 minutes ago, alan_fincher said:


Given how old the figures I have quoted are, I suspect they may b valid only for a narrow beam craft - a wide beam of those heights may well find places where they could not get through.

 

 A few years ago on the Leicester section, we found that narrow boats travelling together had to leave the bottom of some locks singled out, as the cabin of the boat on the non-towpath side would catch the bridge over the lock tail unless that boat moved to the centre of the lock

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51 minutes ago, Tony Brooks said:

No we can't because, as has been said, so often, it depends upon the profile of your boat. A narrowboat can have a higher air draft than a wide boat. Many bridges and tunnels are arches, so the air draft right at the side may only be a very few feet, but in the centre perhaps 10 feet or more.

 

 

It also depends on the water level on the day. If (as there sometimes is) 4" or 6" of water missing from a particular pound, a boat might fit through a tight bridge one day but not on another. 

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This inability to give you THE answer is, as has already been said - but is not unique to the canals.

 

Many road bridges will be signed with painted vertical lines showing the maximum height allowable AT THAT WIDTH and that position under the bridge. So without knowing 'one' we cannot tell you the 'other'

 

 

image.jpeg.23dd175bbb3938698f3a6550431c6bba.jpeg

 

Image result for road bridge showing height in the centre

 

 

 

Edited by Alan de Enfield
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2 hours ago, Alan de Enfield said:

This inability to give you THE answer is, as has already been said - but is not unique to the canals.

 

Many road bridges will be signed with painted vertical lines showing the maximum height allowable AT THAT WIDTH and that position under the bridge. So without knowing 'one' we cannot tell you the 'other'

 

And even then you can be caught out.  Many moons ago I was involved in the transportation of a load which measured 16' 6" high.  Research showed the lowest bridge, which was flat, was marked at 16'9".  All good, and plans approved.  On the day we approached with caution and had a couple of bods up on the load sighting through.  Long story short we touched the bridge.  Fortunately it was a dual carriageway and we had two escort vehicles following line abreast who were gently holding back the traffic.  Reversing out we found the outside lane was a tad higher so squeezed through.  Police arrived due to us causing a reasonable amount of chaos and the inquest started. Turned out the road had been tarmacked a few times and was a bit higher than advertised.  Moral is, trust nobody.🙂

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3 hours ago, perfectlydressed said:

Hi can anyone tell me what the air draft is on the Grand Union for certain please?

 

3 hours ago, IanD said:

Which section(s) of the GU are you asking about?

Well I can tell you that in the sections between the bridges it's mostly unlimited.

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50 minutes ago, Ken X said:

 

And even then you can be caught out.  Many moons ago I was involved in the transportation of a load which measured 16' 6" high.  Research showed the lowest bridge, which was flat, was marked at 16'9".  All good, and plans approved.  On the day we approached with caution and had a couple of bods up on the load sighting through.  Long story short we touched the bridge.  Fortunately it was a dual carriageway and we had two escort vehicles following line abreast who were gently holding back the traffic.  Reversing out we found the outside lane was a tad higher so squeezed through.  Police arrived due to us causing a reasonable amount of chaos and the inquest started. Turned out the road had been tarmacked a few times and was a bit higher than advertised.  Moral is, trust nobody.🙂

 

When my boat was moved even with everything folded down it was still too high when on a standard truck. We had to hire a special (very special) low loader that had a hydraulic bed that was certified to be road-safe when be lowered to 100mm road clearance, everytime they came to a bridge they had to drop the bed, drive thru and then lift it again. Good job we had escorts as well.

 

 

 

21-10-19t small.jpg

Edited by Alan de Enfield
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4 hours ago, alan_fincher said:

Quoted numbers are:

 

Brentford - Berkhamsted 8' 2" (2.49m)

Berkhamsted - Braunston 7' 10" (2.38m)

Braunston - Camp Hill 6'6" (1.98m).

 

However I endorse the remarks that it depends on width and profile of your roof.

Given how old the figures I have quoted are, I suspect they may b valid only for a narrow beam craft - a wide beam of those heights may well find places where they could not get through.

 

Where do you want to get from and to, please?

 

Quoted where?

 

The current CRT published dimensions issued in August 2022 are:

 

8' 9" from Brentford to Long Buckby (by which I suspect it means the bottom of Buckby locks i.e. Whilton)

6' 3" from Long Buckby to the top of Camp Hill locks

 

The historic (and therefore presumably legally binding) headroom from Long Buckby to Camp Hill is 8' 0" so whether the 6' 3" relates to some temporary works, some issue that has arisen since 1967 or the construction of something below 8' 0" I don't know. It could relate to the width vs height issue but CRT dimensions don't appear to make that consideration in general.

 

 

Edited by Captain Pegg
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