C&RT License Survey

[IanD]

14 minutes ago, beerbeerbeerbeerbeer said:

morning,

 

yes, it’s a single use of lock I’m thinking of, 

what happens with the lock when I leave is irrelevant,

isn’t it?

 

we’re comparing water used by one size of boat with another,

 

It makes no difference whether it's one use of a lock by one or more (or no) boats or many uses, the fact remains that the amount of water used -- meaning, transferred from the upper pound to the lower one -- by one lock cycle is exactly the same in all cases, regardless of how big or how many boats are in the lock. Assuming they stay afloat at all times... 😉

 

Widebeams in a wide lock use more water per boat movement than narrowbeams sharing a lock, but the same amount as one boat of any size -- even a canoe -- if sharing doesn't happen. Which is the vast majority of the time...

Edited December 18, 2023 by IanD

[David Mack]

11 hours ago, beerbeerbeerbeerbeer said:

 

A closed lock with a boat in has less water than a closed lock without a boat.

?yes?

Yes, but irrelevant, because we never completely empty the lock (in the way a bath empties when you pull out the plug), we only change the water level between the upper and lower pound levels.

A full lock with a boat floating in it contains the volume of water of the lock chamber from invert level to upper pound level minus the volume occupied by the boat. The same lock with water at the lower pound level contains the volume of water from invert level to lower pound level minus the volume occupied by the boat. So the amount of water transferred into or out of the lock when it is filled or emptied is the difference between those two volumes. And the 'volume occupied by the boat' cancels out when you do the subtraction. So the amount of water required does not vary with the size of the boat (or indeed whether or not there is a boat present).

[Alan de Enfield]

I'm bored with this lock volume / boat volume palaver, can we just get back to complaining about fat boats and non-CCing CCers ?

 

Bah Humbug !

[MtB]

2 hours ago, cowpie said:

What would happen if a boat is in a full lock and completely leak-free lock, ie all paddles closed. Then you lift a ton of ballast out of the boat?  There will not be a ton of inrushing water into the leak free lock.

Then you drop the ton of ballast into the water but because it is more dense than water it will not replace the full ton of water?

CRT advise me they have yet to find a leak-free lock!

 

 

Remind me never to share a lock with you, or anyone else who transits through locks like this...!

 

 

 

 

 

[magnetman]

Reports of idiots in wide beans putting cones and signs on 'their mooring spot' when going to get water. 

 

Things will have to change soon me thinks before the idiots take over. 

 

One thing the CRT need to do yesterday is gain control of their land. Stationary objects on towpaths = not acceptable. 

 

Major works being carried out (welding, cutting, drilling) on towpaths = not acceptable. Use a Boatyard for this. 

 

Get rid of all this inappropriate behaviour on the land and sort it out otherwise its going to all go wrong and get expensive. Just look how much the Ward case on the K&A cost. Outrageous and the place looked like a pie quay site. 

 

 

 

Canals are a public amenity. You don't get people cutting up sheets of MDF in the local park so why is this allowed on towpaths ?

Edited December 18, 2023 by magnetman

[beerbeerbeerbeerbeer]

1 hour ago, David Mack said:

Yes, but irrelevant, because we never completely empty the lock (in the way a bath empties when you pull out the plug), we only change the water level between the upper and lower pound levels.

A full lock with a boat floating in it contains the volume of water of the lock chamber from invert level to upper pound level minus the volume occupied by the boat. The same lock with water at the lower pound level contains the volume of water from invert level to lower pound level minus the volume occupied by the boat. So the amount of water transferred into or out of the lock when it is filled or emptied is the difference between those two volumes. And the 'volume occupied by the boat' cancels out when you do the subtraction. So the amount of water required does not vary with the size of the boat (or indeed whether or not there is a boat present).

Yes,

Im converted (for now)

after rereading and pondering on PaulC’s explanation

..and now your clear explanation makes a lot of sense and makes me see what magnetman was on about now. 
 

I’ll be in agreement 👍

 

(until someone puts a more convincing argument back the other way)

[Momac]

[Paul C]

No

[magnetman]

 

You have to remember that the 15 tonnes of water 'saved' when going into the lock is expelled from the lock (going down) when the level is achieved. If this didn't happen it would not be possible to open the gates. 

So while you may appear to have saved water this is then used up so there was no saving. 

 

 

Going down. 

 

The argument that the Boat has 'pushed water out' into the top pound must mean there is more water in the top pound so water has been saved is defeated because exactly the same amount must be pushed out the bottom of the lock. 

Edited December 18, 2023 by magnetman

[beerbeerbeerbeerbeer]

5 minutes ago, magnetman said:

 

You have to remember that the 15 tonnes of water 'saved' when going into the lock is expelled from the lock (going down) when the level is achieved. If this didn't happen it would not be possible to open the gates. 

So while you may appear to have saved water this is then used up so there was no saving. 

but that’s water ‘returned’ from the lower pound,

 

aren’t we only concerned with the reduced volume of water brought down with the boat from the pound above?

[magnetman]

 

 

The water in the lock must be larger than the water space occupied by the Boat otherwise the Boat would not be floating. 

 

The Boat is a block of water. 

Just now, beerbeerbeerbeerbeer said:

but that’s water ‘returned’ from the lower pound,

 

aren’t we only concerned with the reduced volume of water brought down with the boat from the pound above?

 

How is it 'returned'? 

 

There is no reduced volume brought down. Its impossible for it to make any difference because the Boat is simply behaving as a block of water. The same as any other block of water. A lock with no Boat in it has exactly the same block of water in it its just not a Boat. 

 

 

[beerbeerbeerbeerbeer]

so: the boat displaces water at the top and then displaces water at the bottom,👍

 

but the water at the bottom was/is always there, that water at the bottom is not water brought down with the boat….🤔

or don’t that matter?

[magnetman]

 

Once the Boat is afloat and has completed the initial displacement of water caused by it being placed into the water it can't do anything else than function as a block of water. 

 

Its impossible for this to happen unless the weight of the Boat is altered, it is aground or it is lifted out of the water. 

 

None of these things happen during a lock cycle so ... Boat = block of water. End of story. 

[phillarrow]

The problem with those pics is that you've shaded in an area of water that equates to a 3m depth, but then drawn the canal bed well below this. The way the top drawing is displayed, if the bottom drawing was accurate, the boat would have grounded. 

 

To do this properly, you would need calculate the entire volume of the lock underneath boat in the second pic, both before and afterwards, then subtract the latter from the former. Do the same for the total volume in the first pic. The difference will be the same in both scenarios.

[magnetman]

 

3 minutes ago, beerbeerbeerbeerbeer said:

so: the boat displaces water at the top and then displaces water at the bottom,👍

 

but the water at the bottom was/is always there, that water at the bottom is not water brought down with the boat….🤔

or don’t that matter?

 

The 'water at the bottom' is a smaller amount the bigger the boat. This is because the Boat has shoved out exactly the same amount it apparently saved when it entered the lock. 

 

Think of it like waterline v bottom of Boat. There is a portion of the Boat under the water. This is the key factor. The Boat is not floating on the surface. 

Edited December 18, 2023 by magnetman

[phillarrow]

To add to my initial reply:

 

Add 1m for the depth of water in the lower canal, i.e. what's in the lock below your shaded bit.

 

Total lock volume in the first pic is now: 4 x 20 x 4 = 320. 

After the lock has emptied, it is 4 x 20 x 1 = 80.

Therefore, change in water = 240

 

In the second pic, total volume of water = 320 - 15 = 305

After emptying, total is 80 - 15 = 65

Therefore, change in water = 305 - 65 = 240!

Edited December 18, 2023 by phillarrow
Typo

[IanD]

An easy way to think of this -- imagine the surface of the water with the lock full is like a piston with a lump in it where the boat is. Now push it down by the fall of the lock, the amount of water pushed down and into the lower pound is lock area x lock fall, regardless of the size or shape of the boat lump.

[magnetman]

The Boat is a block of water. 

[Momac]

2 minutes ago, phillarrow said:

The problem with those pics is that you've shaded in an area of water that equates to a 3m depth, but then drawn the canal bed well below this. 

 

How is that a problem? That's how it is isn't it . The boat has to be afloat still with the water in the lock at the lower level. 

its just freehand diagrams , not to scale . 

 

25 minutes ago, Paul C said:

No

Yes

[phillarrow]

Just now, MartynG said:

How is that a problem? That's how it is isn't it . The boat has to be afloat still with the water in the lock at the lower level. 

its just freehand diagrams , not to scale . 

 

See my second reply. It's a problem, because it's not the amount/mass/volume that matters, it's the change. And that change is unaffected by the boat because of the water you left out of the pics.

 

Have a look at the calculations I've done. Your drawings have actually really helped to prove this, you just missed out one vital bit.

[magnetman]

People forget that a significant portion of the Boat is below the waterline. 

 

The Boat does not change its shape during the move. 

Edited December 18, 2023 by magnetman

[Allan(nb Albert)]

30 minutes ago, magnetman said:

 

Once the Boat is afloat and has completed the initial displacement of water caused by it being placed into the water it can't do anything else than function as a block of water. 

 

Its impossible for this to happen unless the weight of the Boat is altered, it is aground or it is lifted out of the water. 

 

None of these things happen during a lock cycle so ... Boat = block of water. End of story. 

First you argued that a boat is a "hole in the water". Now you tell us that a boat is a "block of water". 

 

Next you will be telling the forum gullible that it is both at the same time...

 

 

 

[magnetman]

1 minute ago, Allan(nb Albert) said:

First you argued that a boat is a "hole in the water". Now you tell us that a boat is a "block of water". 

 

Next you will be telling the forum gullible that it is both at the same time...

 

 

 

Its the same thing. A hole in the water is the same as a block of water for all the time it remains afloat. 

[Barneyp]

4 hours ago, Alan de Enfield said:

I'm bored with this lock volume / boat volume palaver, can we just get back to complaining about fat boats and non-CCing CCers ?

 

Bah Humbug !

I think the fact that we can't agree on the "lock volume / boat volume palaver" despite the fact it is a logical fact based problem with a definite correct answer, probably explains why we got nowhere on the rights and wrongs of the licence fee system and surcharges etc, which is far more complicated as it has no overall correct answer (other than "I'm right and if you disagree your wrong"😁)

Edited December 18, 2023 by Barneyp

[magnetman]

 

When the Boat is initially added to the water it creates a hole. Once it is in the water it acts exactly the same as a block of water the same shape as it.