Height of a narrowboat

[PMcC]

Thanks "AIRDRAFT"  I had no idea it was called that many thanks.

Phill

[blackrose]

3 hours ago, Kev's Halcyon said:

Exterior height is usually 6 foot 10 inch. Possibly 2 foot to 2 foot 10 below the waterline, so you generally have 4 to 4 foot 10 above the water line. This will increase with any external fitting standing above the roof.

 

Kevin

Really? Are those the general dimensions? 

I've got an overall height of about 8ft and an airdraft of about 5ft 8in. It's never failed to get under any bridges. I've seen narrowboats with slightly greater (unadorned) airdrafts than my boat.

Edited February 17, 2018 by blackrose

[Dr Bob]

1 hour ago, rusty69 said:

Are you in Sweden?

No, sounds more like Latvia.

[Dr Bob]

42 minutes ago, Tam & Di said:

The height of your craft about water is the airdraft, and you can to some effect change this by adding/subtracting ballast - either solid fixed stuff or stuff like water in your tanks. However as you add more ballast to reduce the airdraft then the boat will sit deeper in the water - i.e. it will have greater draft, making it more problematic on shallow canals.

 

There is a major problem in trying to adjust the boats airdraft via adding/subtracting ballast and that is you have to lug the weight round with you ....so then it is not adjustable.

Far better is to adjust the airdraft by changing the density of the water you crusing on. If you therefore hit a shallow bit of canal, you turn on the salter machine which pumps water into jets on the bottom of the boat, but that water goes through cassettes of salt thus creating a salt water layer under the boat. Salt water is denser than canal water so the boat floats higher. To go under a low bridge or tunnel, instead of circulating the water through the salt cassette to the bottom of the boat mounted jets, you inject air into the water (or even methane if you have a couple of cows on deck) so the water under the boat is now saturated with minute air bubbles thus creating a layer of water with a density less than canal water. The boat therefore sits lower in the water. Air draft can therefore be controlled quite accurately giving about 9.5 inches of variation in air draft. Quite a few boats are using this technology now.

[Tam & Di]

3 hours ago, Kev's Halcyon said:

Exterior height is usually 6 foot 10 inch. Possibly 2 foot to 2 foot 10 below the waterline, so you generally have 4 to 4 foot 10 above the water line.

I'd have thought that overall height of most boats is more than that, but anyway the figures don't allow for the fact that most boats will have a greater draft at the stern than the bow either - i.e. they will have greatest airdraft at the fore end, and if they only draw 12" at the bow they'd have airdraft of 5' 10"

[rusty69]

2 minutes ago, Dr Bob said:

Quite a few boats are using this technology now.

Or just pull the plug out. Simples

[Jen-in-Wellies]

26 minutes ago, Dr Bob said:

There is a major problem in trying to adjust the boats airdraft via adding/subtracting ballast and that is you have to lug the weight round with you ....so then it is not adjustable.

Far better is to adjust the airdraft by changing the density of the water you crusing on. If you therefore hit a shallow bit of canal, you turn on the salter machine which pumps water into jets on the bottom of the boat, but that water goes through cassettes of salt thus creating a salt water layer under the boat. Salt water is denser than canal water so the boat floats higher. To go under a low bridge or tunnel, instead of circulating the water through the salt cassette to the bottom of the boat mounted jets, you inject air into the water (or even methane if you have a couple of cows on deck) so the water under the boat is now saturated with minute air bubbles thus creating a layer of water with a density less than canal water. The boat therefore sits lower in the water. Air draft can therefore be controlled quite accurately giving about 9.5 inches of variation in air draft. Quite a few boats are using this technology now.

Water density is the reason why Standedge Tunnel bookings are only available between March and November. In the Winter, the cold canal water is denser, leading to boats air draft increasing and there being too much risk of them striking the roof. CaRT are installing an air bubble system inside the tunnel to lower the water density for winter passages. It isn't finished yet, but there is a button on the wall by the Marsden end marked "Jacuzzi".

Jen

Edited February 17, 2018 by Jen-in-Wellies

[Alan de Enfield]

16 minutes ago, rusty69 said:

Or just pull the plug out. Simples

Another simple way is to just dig the bottom of the cut a bit deeper for whatever the distance is of the reduced height, this means the water will follow the contour of the bottom and give you more 'head-room' without altering the airdraft of the boat.

 

If the bottom is made gently sloping then there will not be a sudden 'drop-off', or 'step' to negotiate.

[PMcC]

25 minutes ago, Jen-in-Wellies said:

Water density is the reason why Standedge Tunnel bookings are only available between March and November. In the Winter, the cold canal water is denser, leading to boats air draft increasing and there being too much risk of them striking the roof. CaRT are installing an air bubble system inside the tunnel to lower the water density for winter passages. It isn't finished yet, but there is a button on the wall by the Marsden end marked "Jacuzzi".

Jen

What I don't understand is why not just fly over the tunnels surely it would be easier

 

[rusty69]

2 minutes ago, PMcC said:

What I don't understand is why not just fly over the tunnels surely it would be easier

 

Cos you'd need a fly-boat for that.

Edited February 17, 2018 by rusty69

[Dr Bob]

Just now, rusty69 said:

Cos you'd need a fly boat for that.

or even a flying boat

[ditchcrawler]

CRT publish the tunnel dimensions here https://canalrivertrust.org.uk/places-to-visit/standedge-tunnel-and-visitor-centre/boating-through-standedge-tunnel