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whistler49
whistler49

Posted: Sat Nov 02, 2013 6:07pm

Post Subject: Air Draft

I have ordered a new 57' narrow boat and have questioned the builder on the air draft - about 6' is the answer. Fine - what restrictions does that present. CRT tells me the Harecastle Tunnel is 7' 7" - I thought it less that that last time I went through it. Every 'expert' or blog on the internet has different height restrictions on different canals,5'9" appearing to be the lowest. Is there a definitive list that can be relied upon, is 6' air draft acceptable, and is there a need for an article on this in the mag?

Tony-B
Tony-B

Posted: Sun Nov 03, 2013 9:36am

Post Subject: Air Draft

British Waterways used to publish a boat profile guide but this seems to have disappeared with the move to CaRT. The profile of the boat is important when you talk of air draft because most tunnels and bridges are arches that drop down at the sides so the shape of the boat affects the clearance. A boat with vertical cabin sides would need a greater air draft than one with sharply inwardly inclined cabin sides. This means the air draft required to pass under bridges varies from boat to boat. The amount of "stuff" you put on the boat will also alter its air draft. The next problem with giving you a definitive answer is that water levels go up and down - even on canals - while bridge and tunnel heights do not. This means that any air draft given can only ever be a guide. I had hoped that the CaRT Waterway Guides would give some idea of bridge clearance but when I checked for the low railway bridge on the South Stratford canal I found no height data, an omission in my view. I think that an approximate 6ft air draft will only stop you in a very few places like the Froghall tunnel and some of the very low bridges on the less popular routes in the Fens and Withan Drains. However I have not travelled all the system. I do occasionally have to unscrew my radio aerial for really low bridges but that only amounts to once or twice a year. The swing bridge into Bristol Docks and the Stratford bridge I mentioned are cases in point. Although it is difficult getting permission to navigate the Dudley tunnel (which is very low) I know of one determined boater who got that permission and the went to great lengths to ballast his boat down to the required air draft. He used dustbins and children's paddling pools full of water and a load of bricks. Most of use would just use the Netherton tunnel to get to the same place. Likewise until they restore a lot more of the canal beyond Froghall there is little point in trying to pass that tunnel. The varying profile of boats, the varying water levels and the times scaffolding is hung under structures all mean that there can never be a definitive maximum air draft height given for any structure, this makes it unsuitable as a magazine article in my view. The Editor may think differently though. I am sure there will be very few parts of the system you will not be able to visit as long as you keep your roof free of clutter. For example specify the low profile "flying saucer" roof vents rather than mushrooms. Place and flue at the lowest part of the roof or in the centre. I regret that all my Nicholson's Guides are on the boat so I can not consult them on your behalf. Tony Brooks

wirren
wirren

Posted: Sun Nov 03, 2013 7:51pm

Post Subject: Air Draft

Hi Ian, Our Sea Otter has a 6' air draft in its specification . We have been through the Harecastle 7 times now & sometimes in the middle low section it's nail biting stuff, just got to keep the boat in the centre. It's the arch sides that you have to keep away from. I fit a go cart tyre on the front roof corners for peace of mind. I also aim to be at the front of any queue ( even if I have to wait ) it's best to go through at reasonable pace as it can help to maintain a straight line. Enjoy your boat, I'm sure you will. Mark.

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