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mattsbsmith

Grand Union Paddington Arm Headroom

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Hi,

 

I've been looking at this page on the CRT website: https://canalrivertrust.org.uk/enjoy-the-waterways/canal-and-river-network/paddington-arm-grand-union-canal

 

It states that the headroom is 2.08m (6ft 9") and the draught is 1.28m (4ft 2"). I just wanted to check that I understand this correctly. 

 

Our boat has a draught of 24" (2 ft) so I assume we are okay on that measurement. 

 

As far as I understand, the headroom is the distance from the waterline to the lowest bridge. Is that correct? 

 

I appreciate headroom may of course change as the waterline changes but I assume CRT have listed the minimum it will ever be.

 

The reason I am checking is because the overall height of our boat (from the baseplate to the roof) is 2.5m (8ft 2"). The amount that sits above the waterline is 1.89m (6ft 2") so if the headroom measurement is as I understand we should be fine here too. However, if I've understood it incorrectly and headroom is equivalent to the total height of the boat, we will be in trouble when trying to navigate. The width is 13 feet in case that is of relevance (the CRT page states 14 ft as the max width).

 

Any guidance would be much appreciated.

 

Thanks,

Matthew

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Headroom is the distance above the water.  Easy to interpret for a girder bridge with a flat underside, less so for an arched bridge, where the headroom at a particular width is of more use.

I don't know the Paddington arm well enough to say whether the lowest bridge is arched or flat.

N

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On a canal the air draught would normally be measured with the canal at weir level. At times the water level could be higher, for example after heavy rain, or at the downwind end of a pound if there is a strong wind blowing along the canal.

 

On arched bridges the measurement is most usually taken to the highest point of the arch.

 

 

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1 minute ago, roland elsdon said:

Tunnel?

I was wondering about the tunnels on the Regents, but it is probably nearly 40 years since I last went through there. I have a distant recollection that the Humber Keel “Beecliffe” struggled through one of them in the 70’s, but presumably got through the rest of the Regents and Paddington Branch OK. 
 

Again I don’t really know but I don’t recall any “arched” bridges In the hump back sense along that stretch, more “flat” or gently curved, so I guess the OP should be fairly comfortable. The lowest bridges are often railway bridges (for obvious reasons of gradient) and these are usually flat.
 

Local knowledge needed!

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11 minutes ago, Balliol said:

On arched bridges the measurement is most usually taken to the highest point of the arch.

 

 

I'm not convinced this is true - the dimensions are normally for the largest craft so a profile will have been assumed - an air draught over a given width

 

Bit of a problem if the boat your using doesn't match the profile though

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18 minutes ago, magpie patrick said:

I'm not convinced this is true - the dimensions are normally for the largest craft so a profile will have been assumed - an air draught over a given width

 

Bit of a problem if the boat your using doesn't match the profile though

I agree. To be meaningful the published maximum air draught must apply over the full extent of the published maximum width. It therefore follows that all arched bridges would have a maximum height in excess of the published maximum craft dimension and that the published maximum air draught is not necessarily a singular critical limit that can never be exceeded.

 

JP

Edited by Captain Pegg

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If the maximum height of your boat above water level is 6ft 2in, you shoudl be fine on the Paddington Arm. As others have said, the critical point will be at the sides of arched bridges.

 

Where is the boat at present and how far are you thinking of taking it? Just pottering up an down the Paddington Arm will soon become tedious, and if you are a Continiuous Cruiser is unlikely to satisfy CRT.

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42 minutes ago, mattsbsmith said:

t states that the headroom (airdraft) is 2.08m (6ft 9") and the draught is 1.28m (4ft 2"). I just wanted to check that I understand this correctly. 

The airdraft may well be lower for a widebeam boat.

Are you talking about a Narrowboat or a 'fatty' ?

 

Just to explain

If your 'boat' is narrow your airdraft is the 'red' line height.

If you boat is 'wide' than your airdraft is the 'yellow' line height.

 

 

Inked108002-M_LI.jpg

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10 minutes ago, Alan de Enfield said:

The airdraft may well be lower for a widebeam boat.

Are you talking about a Narrowboat or a 'fatty' ?

 

Just to explain

If your 'boat' is narrow your airdraft is the 'red' line height.

If you boat is 'wide' than your airdraft is the 'yellow' line height.

 

 

Inked108002-M_LI.jpg

That narrowboat is one of those East West ones isnt it....

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22 minutes ago, Alan de Enfield said:

The airdraft may well be lower for a widebeam boat.

Are you talking about a Narrowboat or a 'fatty' ?

 

Just to explain

If your 'boat' is narrow your airdraft is the 'red' line height.

If you boat is 'wide' than your airdraft is the 'yellow' line height.

 

 

Inked108002-M_LI.jpg

That illustrates the point nicely but surely the published maximum craft dimensions are complementary and any craft inside both will fit?
 

If you published the width as per your yellow outline and the height of your red outline as the single limiting dimensions it would include craft that don’t fit. Those dimensions are legally binding on CRT.

 

JP

Edited by Captain Pegg

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You won't have any difficulty down the Paddington arm and will no doubt be OK through the Islington tunnel to Kings Cross as we were in our 13' 6" beam barge with quite a big airdraft. We moored outside the Canal museum after prior arrangement. Fantastic experience in the centre of the capital.

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27 minutes ago, Alan de Enfield said:

The airdraft may well be lower for a widebeam boat.

Are you talking about a Narrowboat or a 'fatty' ?

As they say it is 13 feet wide, I don't think it is a narrow boat!

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3 minutes ago, alan_fincher said:

As they say it is 13 feet wide, I don't think it is a narrow boat!

 

Thank you.

 

Fatal error - didn't read to the last line.

 

That information could have an effect on the available airdraft and the C&RT figure is probably incorrect for that beam.

Edited by Alan de Enfield

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1 minute ago, David Mack said:

And with a dip in the canal under the bridge like that, short length boats might get through where long boats of the same airdraft might not.

Mind you - a drop of water would assist !!

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1 hour ago, magpie patrick said:

I'm not convinced this is true - the dimensions are normally for the largest craft so a profile will have been assumed - an air draught over a given width

 

That depends upon whether you are talking about the bridge dimensions or the maximum permissible vessel size.

 

The EA bridge heights on the Thames are to the crown of the arch, as are PLA figures, as are French figures. BW / CRT have often quoted bridge heights on some waterways as the height to the crown. However, I think that the simple answers are. (1) that there may be more than one way of expressing the bridge size, and (2) that the listed sizes are very often conservative. 
 

In respect of the latter the headroom for the Paddington Branch is variously listed between 6’ 9” and 7’ 4”. 

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Hi all, 

 

Thanks so much for your responses. They're really very helpful (and much more useful than the response I got from CRT!). 

 

The clarification of the headroom and the additional info re: bridge calculations is very useful. To summarise, it looks like we should be fine.

 

To answer David's question, we actually have a residential mooring so won't be heading too far in either direction (we actually only want to potter about in the school holidays!) I was also recommended the Nicholson guide so will pick one of those up. 

 

Thanks again, 

Matthew 

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I think you will find that the lowest bridge on the arm is the wooden footbridge at Smith's Farm just south of Western Avenue Bridge 17B.

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On 19/03/2020 at 11:20, Up-Side-Down said:

I think you will find that the lowest bridge on the arm is the wooden footbridge at Smith's Farm just south of Western Avenue Bridge 17B.

I was led to believe that the lowest bridge in those parts is the one by Packet Boat Marina. FOR NARROWBOATS, if you can get through there, you can go most places.

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The Islington tunnel is well arched. The charity boat based at Paddington often goes through it, BUT they have big fenders bolted to the cabin sides where the roof contacts the arch if the steerer misjudges.

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53 minutes ago, monkeyhanger said:

I was led to believe that the lowest bridge in those parts is the one by Packet Boat Marina. FOR NARROWBOATS, if you can get through there, you can go most places.

Not on the Paddington arm, the bridge above Cowley lock is the one that normally sorts out the question of headroom - many a broads style cruiser has been 'modified' there!

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I never had a problem anywhere on the Paddington arm on a 12ft widebeam. Never had a problem with bridges or tunnels on broad canals anywhere else either. 13ft is pushing it a bit but as long as your cabin sides have some tumblehome and the roof has some curve to it you should be ok.

Edited by blackrose

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On 18/03/2020 at 18:59, Alan de Enfield said:

The airdraft may well be lower for a widebeam boat.

Are you talking about a Narrowboat or a 'fatty' ?

 

Just to explain

If your 'boat' is narrow your airdraft is the 'red' line height.

If you boat is 'wide' than your airdraft is the 'yellow' line height.

 

 

Inked108002-M_LI.jpg

Don't forget to include the height of the low loader the boat is sat on! Also, you'll be limited to just the left hand side of the bridge and then have the problem of crashing head first in to the oncoming car that is on the wrong side of the road. The dip in the level under the arch is useful though. Why can't CaRT do something like that? I've only seen the Paddington Arm once, when I went for a walk while waiting to meet someone arriving at the station. I don't remember any bridge looking like that.

Jen

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