Lockage Water Used

[Señor Chris]

Going uphill:

To fill the lock requires a volume of water equal to the volume of the lock, less the boats displacement.

No, it's one lock-full, regardless of displacement.

 

A [possibly] simpler way of looking at things:

 

The amount of water 'used' is just the balance of water drawn from the upper pound, remembering that the lock must be refilled on the way down if full to begin with. It is only therefore necessary to consider movements that affect the upper pound.

 

Down:

Boat enters lock - pound gains displacement from lock

Lock refilled after boat leaves - pound loses lock-full

 

Up:

Lock filled - pound loses lock-full

Boat leaves lock - pound loses displacement to lock

 

So the only difference between the two is the displacement - a gain going down, a loss going up.

 

Exactly as Mr Jebb described.

[Gordias]

If the same boat makes a round trip the effects of the boat's displacement cancel out, and if the analysis starts with the lock set correctly, the "average per boat using the lock" is half a lockful.

 

I wonder if Mr Jebb's point was that for a canal that's used mostly for series of loaded boats passing through a lock, unloading, and returning empty, you'd prefer the loaded ones to be descending?

 

Either way, the best way to "save" water (assuming you don't mind the suggestions from boat users who would prefer not to wait) is to alternate one boat in each direction, so no water is ever "wasted" to set the lock.

 

... tempted to include a joke about CaRT and technology here, but decided against it

Edited December 2, 2015 by Gordias

[tidal]

There are times when I get a feeling of déjà vu on here

[Steilsteven]

There are times when I get a feeling of déjà vu on here

I'm sure I've heard of that before.

 

Keith

[tidal]

[NickF]

So going down moves water uphill!

Not exactly, the transfer of water from lock to pound occurs when the boat enters the lock and all is level! When a boat sails into a lock it has to displace some of the water from the lock, the only place for this water to go is back into the pound the boat has just left.

[Ray T]

Not exactly, the transfer of water from lock to pound occurs when the boat enters the lock and all is level! When a boat sails into a lock it has to displace some of the water from the lock, the only place for this water to go is back into the pound the boat has just left.

 

You often see the effect of this if a single boat enters a double lock going down, with one gate closed. The closed gate will open as the boat enters.

 

ETA. This happens on the Calcutt Flight.

Edited December 2, 2015 by Ray T

[ditchcrawler]

OK, what about the Falkirk wheel, I maintain if there is a steady row of boats descending and no one going up then water is transferred from the basin to the upper canal.

[Chewbacka]

A boat enters the top chamber, pushing it's displacement of water out of the chamber. The chamber goes down containg a chamberful less the displacement. At the bottom the doors open and the boat leaves and water must flow in to replace the boat. The chamber going up contains only water, so a single chamber full.

 

So -

going down = chamberful Less boat displacement

going up = chamberful of water

[Loafer]

A boat enters the top chamber, pushing it's displacement of water out of the chamber. The chamber goes down containg a chamberful less the displacement. At the bottom the doors open and the boat leaves and water must flow in to replace the boat. The chamber going up contains only water, so a single chamber full.

 

So -

going down = chamberful Less boat displacement

going up = chamberful of water

 

Not if there's a similar boat going up though?

[Chewbacka]

But the question - post 58 - was "I maintain if there is a steady row of boats descending and no one going up" which is what I was taking issue with.

[Scholar Gypsy]

OK, what about the Falkirk wheel, I maintain if there is a steady row of boats descending and no one going up then water is transferred from the basin to the upper canal.

 

Very nice. The energy argument does work in this case.

 

Moving the wheel by 180^o takes a fixed amount of energy to overcome frictional losses (the same as to boil a kettle, I recall). This is the same whether there is a boat in the cassion or not. So if a boat moves from upper level to lower level then conservation of (gravitational potential) energy means that an equal mass of water must move uphill. And vice versa. If this was not the case then you would have created a perpetual motion machine.

 

Of course in this case (neglecting losses and leaks) the water levels above and below the wheel would be unchanged by the passage of a boat.The upper level would have more water in it, but less boat, so the water level would be the same.

 

The Falkirk wheel is just a machine, in the formal sense of the word. So is a lock. So is the Anderton lift.

[Chewbacka]

 

...............The Falkirk wheel is just a machine, ..................

Not JUST a machine, but a very elegant machine

[mayalld]

No, it's one lock-full, regardless of displacement.

 

A [possibly] simpler way of looking at things:

 

The amount of water 'used' is just the balance of water drawn from the upper pound, remembering that the lock must be refilled on the way down if full to begin with. It is only therefore necessary to consider movements that affect the upper pound.

 

Down:

Boat enters lock - pound gains displacement from lock

Lock refilled after boat leaves - pound loses lock-full

 

Up:

Lock filled - pound loses lock-full

Boat leaves lock - pound loses displacement to lock

 

So the only difference between the two is the displacement - a gain going down, a loss going up.

 

Exactly as Mr Jebb described.

 

The whole displacement question is a red herring.

 

The issue is very much one of how much is taken from the top pound

 

Consider as a starting position;

 

• A single lock between 2 pounds
• Both pounds start at exactly weir level
• For the purposes of measurement, the weir of the lower pound doesn't run to waste, but instead runs into a reservoir that is equipped to back-pump to the upper pound.
• The lock contains 150,000 litres of water
• The difference between the upper and lower levels is 100,000 litres
• Our boat displaces 25,000 litres

Look at various operations;

• Our boat is in the lower pound, but the lock is full. We empty the lock for passage. 100,000 litres runs over the weir to the reservoir
• The lock is empty, we motor in, and fill the lock from the upper pound. Once the boat reaches the upper level, we pump 100,000 litres from the reservoir to refill the upper pound.
• We decide to go back down. As we empty the lock, 100,000 litres flow over the weir.
• We now refill the empty lock, and backpump 100,000 litres from the reservoir to fix the level in the upper pound.

[NickF]

 

 

The whole displacement question is a red herring.

 

The issue is very much one of how much is taken from the top pound

 

Consider as a starting position;

 

• A single lock between 2 pounds
• Both pounds start at exactly weir level
• For the purposes of measurement, the weir of the lower pound doesn't run to waste, but instead runs into a reservoir that is equipped to back-pump to the upper pound.
• The lock contains 150,000 litres of water
• The difference between the upper and lower levels is 100,000 litres
• Our boat displaces 25,000 litres

Look at various operations;

• Our boat is in the lower pound, but the lock is full. We empty the lock for passage. 100,000 litres runs over the weir to the reservoir
• The lock is empty, we motor in, and fill the lock from the upper pound. Once the boat reaches the upper level, we pump 100,000 litres from the reservoir to refill the upper pound.
• We decide to go back down. As we empty the lock, 100,000 litres flow over the weir.
• We now refill the empty lock, and backpump 100,000 litres from the reservoir to fix the level in the upper pound.

 

Nicely put! So all is well as long as you don't crane your boat out at any stage! Does you argument work going over a summit or through a sump pound? I think it probably does , displacement not making any difference but I can't quite get my head round it.

[Machpoint005]

My 2 penneth. Assume your boat weighs 30 tons and exactly fits the confines of the lock, which contains 30.1 tons of water. You displace, back into the upper pound ( assume you're going downhill) that 30 tons of water leaving the .1 tons in the lock to float you. You release that into the lower pound, open the gates and you've only used .1 tons of water.

Going up the same happens, you displace all but the .1 tons back into the lower pound, close the gates, and it only takes .1 tons to fill the lock (because the boat is taking up the rest of the lock.). A large boat therefore uses less water that a small one to operate a lock.

Bob

 

Look up the Principle of Archimedes some time. The weight of the boat exactly displaces the same weight of water. If it didn't the boat would either sink or rise up majestically into the sky (although air is also a fluid...)

[Gordias]

Dave

 

Your example is a round trip, and the displace differences cancel out. IMO it's the most realistic scenario though, so the result is "more correct" than the single ascent or descent examples.

 

Here's what happens on the way down, from the natural starting point.

 

Initial conditions:

• A boat in the upper pound
• Lock empty (i.e. at the level of the lower pound)

 

Abbreviations:

• One boat displacement of water = 1B
• One Lockful of water = 1L

 

A reminder (NB: this is consistent with Dave's post and as far as I remember all the others in this thread, but I've seen it handled incorrectly elsewhere):

• Emptying a lock releases 1L of water regardless of whether it's empty or has boat(s) in it. This assumes the boat isn't on the bottom after the lock is emptied of course

 

Actions and effects on the amount of water:

• Lock is filled.
  • 1L of water is transferred from the Upper Pound into the lock. We have to assume this water is replaced to bring the pound to its normal level before the lock is isolated from the upper pound.
• Boat in Upper Pound enters the lock
  • 1B of water is transferred from the lock to the upper pound. This doesn't affect the water level in the pound or the lock.
• Lock is emptied
  • 1L of water is transferred through the lower pound - it may be "lost", or (as in this scenario) transferred into a suitable reservoir.
• The boat leaves the lock
  • 1B of water is transferred from the pound to the lock.This doesn't affect the water level in the pound or the lock.

 

Now we can see what's happened to the water:

• The upper pound has lost 1L - 1B of water
• The lock is back where it started, at the level of the lower pound
• 1L of water has been released into the reservoir below the lower pound
• The lower pound has lost 1B of water (replacing the boat in the lock)

 

Going the other way does the same thing in reverse, so a round trip answer with the same boat shows 2L being consumed from the upper pound, and both pounds back where they started.

Edited December 3, 2015 by Gordias

[Machpoint005]

 

 

The whole displacement question is a red herring.

 

 

Exactly. For the reason given above.

Forget about the boat's displacement - it is utterly irrelevant.

[Steilsteven]

Not exactly, the transfer of water from lock to pound occurs when the boat enters the lock and all is level! When a boat sails into a lock it has to displace some of the water from the lock, the only place for this water to go is back into the pound the boat has just left.

I know this thread will go on for a long time yet because it is very hard to convince anyone of what is actually happening, apart from setting up a pump and a huge container next to a lock.

 

Where people go wrong with this ( myself included until I got my head around it ) is that they get stuck with the idea that the upper and lower pounds are separate from each other, they aren't!

 

When the boat enters the lock from the upper pound, it has already entered the lower pound because the water at the bottom of the lock ( up to the level of the lower pound ) IS the lower pound.

 

No water gets pushed into the upper pound at all.

 

Keith

[Machpoint005]

I see what you mean but it's merely a question of definition (or semantics). You could equally argue that when opening the top gate on a full lock the lock is part of the UPPER pound.

[Hawkmoth]

 

Look up the Principle of Archimedes some time. The weight of the boat exactly displaces the same weight of water. If it didn't the boat would either sink or rise up majestically into the sky (although air is also a fluid...)

Isn't that exactly what I said. You displace the 30 ton weight of your craft back into the upper pound.

Bob

[Machpoint005]

Isn't that exactly what I said. You displace the 30 ton weight of your craft back into the upper pound.

Bob

 

Your account also suggests that only 0.1 tonnes of water passes into the lower pound, which would mean that the process would be very quick. A moment's thought would tell you that the lock empties in the same time (all else being equal) regardless of the size of the boat, or indeed regardless of whether there's a boat in there at all.

 

(OK we all know that to empty a 'boatless' lock we fling the paddles wide open, which we wouldn't do if the boat was present, but the same amount of water still passes through the paddles).

Edited December 3, 2015 by Machpoint005

[ditchcrawler]

OK any bets on how long this thread will run for?

[cuthound]

I'm amazed, 4 pages in and no one has critisised CRT about leaking lock gates

[Steilsteven]

I see what you mean but it's merely a question of definition (or semantics). You could equally argue that when opening the top gate on a full lock the lock is part of the UPPER pound.

 

Yes.

 

Keith