C&RT License Survey

[agg221]

1 hour ago, IanD said:

This whole idea that boat displacement has any effect on water usage in a lock is wrong, the above post which says it's just lock area x lock fall is correct.

 

Imagine you're going down and the lock is full. When you go into the lock the water level doesn't change, regardless of the size of boat. Now empty the lock, the water level (drawn from below the boat) falls by the drop regardless of size of boat, so the water used is the same. Now open the bottom gates; moving the boat out of the lock doesn't change the water level.

 

One lock turn -- in either direction -- uses the same amount of water whether the lock has one or two narrowboats or one wideboat in it, or indeed no boat at all.

Got it. I had factored in that the volume of water in the lock at the start of the cycle is dependent on the displacement, but not that the amount of water at the end of the cycle is comparably dependent on displacement and therefore the total water transferred is identical.

 

The only relevant factor remaining as a difference between narrow and wide beam is that generally two narrowboats can share a lock whereas two widebeams can't.

 

Alec

Edited December 16, 2023 by agg221

[davidg]

31 minutes ago, agg221 said:

Got it. I had factored in that the volume of water in the lock at the start of the cycle is dependent on the displacement, but not that the amount of water at the end of the cycle is comparably dependent on displacement and therefore the total water transferred is identical.

 

The only relevant factor remaining as a difference between narrow and wide beam is that generally two narrowboats can share a lock whereas two widebeams can't.

 

Alec

 

Well done Grasshopper, you have chosen the path of wisdom. Now spread the word and put an end to this old canard.

[ditchcrawler]

What about the Falkirk wheel with boats just coming down ?

[Momac]

2 hours ago, IanD said:

This whole idea that boat displacement has any effect on water usage in a lock is wrong, the above post which says it's just lock area x lock fall is correct.

 

Imagine you're going down and the lock is full. When you go into the lock the water level doesn't change, regardless of the size of boat. Now empty the lock, the water level (drawn from below the boat) falls by the drop regardless of size of boat, so the water used is the same. Now open the bottom gates; moving the boat out of the lock doesn't change the water level.

 

One lock turn -- in either direction -- uses the same amount of water whether the lock has one or two narrowboats or one wideboat in it, or indeed no boat at all.

As a boat moves along the canal it displaces water  from in front of the boat to behind the boat. The weight of water displaced is the same as the weight of the boat.

So as the boat enters a lock it displaces water out of the lock into the canal behind the boat.

The water level does not change .

Lets say there is  500 Tonnes of water in the lock and the boat has a displacement of 15 Tonnes.

When the boat moves into the lock this causes 15 Tonnes of water to be displaced  so there is 15 Tonnes of boat in the lock and 485 Tonnes of water .

So when the lock operates it needs to move 485 Tonnes of water ..

As the boat moves out of the lock it displaces 15 Tonnes of water from the canal back into the lock.

 

 

 

[Ianws]

6 minutes ago, MartynG said:

As a boat moves along the canal it displaces water  from in front of the boat to behind the boat. The weight of water displaced is the same as the weight of the boat.

So as the boat enters a lock it displaces water out of the lock into the canal behind the boat.

The water level does not change .

Lets say there is  500 Tonnes of water in the lock and the boat has a displacement of 15 Tonnes.

When the boat moves into the lock this causes 15 Tonnes of water to be displaced  so there is 15 Tonnes of boat in the lock and 485 Tonnes of water .

So when the lock operates it needs to move 485 Tonnes of water ..

As the boat moves out of the lock it displaces 15 Tonnes of water from the canal back into the lock.

 

 

 

3% loss through displacement is probably negligible compared to the loss from gates between boats using them. 

[peterboat]

3 hours ago, agg221 said:

I believe that is correct. My point was that in consequence different types of boat will use different volumes of water. The unknown is whether the average (mean) narrowboat has more or less than half the displacement of the average widebeam. I am presuming more, on the grounds that the average length of narrowboats is likely to be around 50' (not tested, but 57' is a very popular length and has been for many years) and the average length of a widebeam is more like 60' as they have generally been built by a smaller number of builders over a shorter period. However, the average beam of a narrowboat is 7' whereas the average beam of a widebeam is not 14', more like 12'. Not allowing for swims (which given how bluff many modern boats are seems like it wouldn't change the figures much), that gives a surface area of 350sq.ft for a narrowboat and 600sq.ft for a widebeam. Assuming the same draft, that would mean the widebeam uses more water per lock than a pair of narrowboats.

 

My figures could be wrong, but I don't know where to get better data from and the difference appears to be sufficient that the principle would still apply if there was considerable variance.

 

What probably makes more difference though is that to lock through two widebeams takes about twice as much water as to lock through two narrowboats (should two come along at once and be going the same way).

Alec

A widebeam will use less water as it displaces more. 

[Momac]

10 minutes ago, Ianws said:

3% loss through displacement is probably negligible compared to the loss from gates between boats using them. 

I agree but that's not the point.

 

32 minutes ago, peterboat said:

A widebeam will use less water as it displaces more. 

True but water used by boats using  locks is not really significant in the scheme of things as far as maintaining the canals is concerned. Even with no boats moving the canals will lose water eg. through leaky gates and evaporation which will probably be far more than any loss caused by boats using locks.

So in that respect wide beam or not does not consume any more or any less water resources.  

 

As far as resources like drinking water and waste disposal is concerned this is more a function of numbers of people and numbers of days out on the waterways . But those things do not come into the licensing fee calculation. 

 

[Mike Todd]

3 hours ago, IanD said:

This whole idea that boat displacement has any effect on water usage in a lock is wrong, the above post which says it's just lock area x lock fall is correct.

 

Imagine you're going down and the lock is full. When you go into the lock the water level doesn't change, regardless of the size of boat. Now empty the lock, the water level (drawn from below the boat) falls by the drop regardless of size of boat, so the water used is the same. Now open the bottom gates; moving the boat out of the lock doesn't change the water level.

 

One lock turn -- in either direction -- uses the same amount of water whether the lock has one or two narrowboats or one wideboat in it, or indeed no boat at all.

When a boat goes into a full lock, it displaces its volume back into the pound above. This affects the calculation.

[Momac]

3 minutes ago, Mike Todd said:

When a boat goes into a full lock, it displaces its volume back into the pound above. This affects the calculation.

Almost . 

The volume of water displaced is the volume of the boat below the water line.

 

[IanD]

54 minutes ago, Mike Todd said:

When a boat goes into a full lock, it displaces its volume back into the pound above. This affects the calculation.

No it doesn't. When the boat is outside the lock, the water is at a given level. When it moves into the lock, the water level doesn't change, so this doesn't "use" any water -- meaning, water that has to be replaced.

1 hour ago, peterboat said:

A widebeam will use less water as it displaces more. 

Nope. Really, just nope. The same amount of water is "used" (moved from above lock to below lock) regardless of how many boats of what size are in the lock when it empties or fills.

 

Go and make a drawing showing the state of the (full) lock before the boat enters it, after the boat enters it, after the boat has gone down in the lock, and after the boat has left the lock. The amount of water moved from the upper pound to the lower one -- "used" -- is the same in all cases, it's the drop in water level (the fall of the lock) multiplied by the area of the lock.

 

Archimedes understood this, but it seems that you don't... 😉

Edited December 16, 2023 by IanD

[Guest]

5 minutes ago, IanD said:

No it doesn't. When the boat is outside the lock, the water is at a given level. When it moves into the lock, the water level doesn't change, so this doesn't "use" any water -- meaning, water that has to be replaced.

Nope. Really, just nope. The same amount of water is "used" (moved from above lock to below lock) regardless of how many boats of what size are in the lock when it empties or fills.

 

What was it you said earlier this evening?

 

Oh yes this.....

 

"This must be the biggest display of pointless "mine's bigger than yours" willy-waving on the forum for some time... 😉"

 

Hypocrite.

[IanD]

5 minutes ago, M_JG said:

 

What was it you said earlier this evening?

 

Oh yes this.....

 

"This must be the biggest display of pointless "mine's bigger than yours" willy-waving on the forum for some time... 😉"

 

Hypocrite.

Why don't you just take your troll postings over to Thunderboat and try and wind people up there instead? 😞

 

Meanwhile, Archimedes was still right... 😉

[Guest]

Just now, IanD said:

Why don't you just take your troll postings over to Thunderboat and try and wind people up there instead? 😞

 

Meanwhile, Archimedes was still right... 😉

 

I haven't been on Thunderboat for about two years, probably longer.

 

If you ever took an occasional step back you would realise why people respond to you as they do.

[phillarrow]

16 minutes ago, IanD said:

No it doesn't. When the boat is outside the lock, the water is at a given level. When it moves into the lock, the water level doesn't change, so this doesn't "use" any water -- meaning, water that has to be replaced.

Nope. Really, just nope. The same amount of water is "used" (moved from above lock to below lock) regardless of how many boats of what size are in the lock when it empties or fills.

 

Go and make a drawing showing the state of the (full) lock before the boat enters it, after the boat enters it, after the boat has gone down in the lock, and after the boat has left the lock. The amount of water moved from the upper pound to the lower one -- "used" -- is the same in all cases, it's the drop in water level (the fall of the lock) multiplied by the area of the lock.

 

Archimedes understood this, but it seems that you don't... 😉

I don't think this is right?

 

Think about your drawing:

In an empty lock the entirety of the volume of the pound is made up of water. When the gates are opened, some of that water goes into the lock below until they are level.

 

Now draw it again from side on with a boat in it. You're right that the water level doesn't rise when the boat enters the top pound. However, there's now something new as well the water in that pound, i.e. a boat. In order for the water level to stay the same, and for the boat to be in the pound, some water MUST have been displaced backwards out of the pound. Therefore, when the gates open and the level drops, it takes less water volume to do so. Then, when the boat leaves the pound, it 'pushes' water from the lower level back into the pound. 

 

In both scenarios, the levels (heights) of the pound stays the same, but surely there is less total water in the pound in the second scenario?

Edited December 16, 2023 by phillarrow
Typo

[Momac]

11 minutes ago, IanD said:

 When the boat is outside the lock, the water is at a given level. When it moves into the lock, the water level doesn't change

This is correct

The water level does not change because the water displaced by the boat is displaced  out of the lock.

 

[Arthur Marshall]

3 minutes ago, M_JG said:

 

What was it you said earlier this evening?

 

Oh yes this.....

 

"This must be the biggest display of pointless "mine's bigger than yours" willy-waving on the forum for some time... 😉"

 

It beats the nonsensical argument about surcharges and who hates who more. Thank gods for thread drift , say I.

Anyway, the displacement. A boat displaces water in the pound it's in, and an open lock is just an extension of the entire pound. So, if a boat is in the pound, it's already displaced that volume of water over the entire pound, including the open lock. So going into it will make no difference whatsoever - a boat doesn't just carry its displacement along with it like a cellar.

It's like the old paradox of why a bullet can never hit a running man.

[Momac]

4 minutes ago, Arthur Marshall said:

- a boat doesn't just carry its displacement along with it like a cellar.

 

That would be good way to think of it .

Once the lock gates are closed the weight in the lock does not change compared to the empty lock with the gate open or closed  . But the weight in the lock is now part water and part boat . The boat has displaced some water equal to the weight of the boat.

 

[Ianws]

2 hours ago, MartynG said:

I agree but that's not the point.

 

True but water used by boats using  locks is not really significant in the scheme of things as far as maintaining the canals is concerned. Even with no boats moving the canals will lose water eg. through leaky gates and evaporation which will probably be far more than any loss caused by boats using locks.

So in that respect wide beam or not does not consume any more or any less water resources.  

 

As far as resources like drinking water and waste disposal is concerned this is more a function of numbers of people and numbers of days out on the waterways . But those things do not come into the licensing fee calculation. 

 

I don't understand why you say that's not the point then straight away go on to make exactly the same point.

[LadyG]

With respect to usage of Elsan/pumpout, I would argue that the single boater who CCs uses that particular facility less over 52 weeks than a family of four using their boat 15 weeks. I've never seen this argument discussed.

Quite a lot of cc boaters I have seen don't live on board , they just move every second weekend. Presumably they use the boat for family holidays when weather is suitable. So just classing cc as being charged more because they use facilities more is too simplistic, probably incorrect in many cases.

Let's face it, CRT need more cash, and one way is to charge a premium to those likely to pay.

[Momac]

10 minutes ago, Ianws said:

I don't understand why you say that's not the point then straight away go on to make exactly the same point.

My point is/was the weight of the boat in the lock  reduces the weight of water that the lock has to move compared to an empty lock. Others are suggesting otherwise.

I agree with your new but related point that  its all insignificant in the scheme of things. 

I hope this helps.

[Ianws]

16 minutes ago, MartynG said:

My point is/was the weight of the boat in the lock  reduces the weight of water that the lock has to move compared to an empty lock. Others are suggesting otherwise.

I agree with your new but related point that  its all insignificant in the scheme of things. 

I hope this helps.

Another factor could be that the relative amounts displaced by different boats are pretty irrelevant compared to the frequency the  particular lock is worked.

 

 

 

[Paul C]

Think of it like this............a lock contains (say) 200m3 of water when its empty, and (say) 1000m3 of water when its full (no boat in it).

 

(With a 20t boat in it, the figures are 180m3 and 980m3).

 

To get from empty to full needs 800m3 of water, irrespective of if there's a boat in it or not. The formula is simply:

 

length of lock x width of lock x rise

 

NOTICE THAT THE DISPLACEMENT OF THE BOAT(S) IS NOT A FACTOR HERE!!!

 

So, a single boat transiting needs 800m3. If its a broad lock and 2 narrowboats can fit in, each of those needs 400m3 to transit the lock (800/2).

[Peanut]

Will this help.

 

Suppose I have a ten ton boat.

 

I travel along the canal and the boat moves ten tons of water out of the way as it passes along. Water going from the in front of the boat to fill in behind.

 

I now come to go down a lock, suppose that a full lock contains one hundred tons of water.

 

As I enter the lock, I displace ten of those tons back into the top pound, and close the gates.

 

There are now ninety tones of water in the lock, and ten tones of boat, as Archimedes applies.

 

I lower the lock to the level of the lower pound, and one hundred tons of water empties from the lock, ten of those tones are the water displaced by the boat from the bottom of the lock.

 

Opening the lower gates, the boat leaves the lock and displaces ten tones of water from the lower pound back into the lock, just as it would have done when travelling along the upper pound.

 

This is independent of the boat's weight.

[peterboat]

2 hours ago, IanD said:

No it doesn't. When the boat is outside the lock, the water is at a given level. When it moves into the lock, the water level doesn't change, so this doesn't "use" any water -- meaning, water that has to be replaced.

Nope. Really, just nope. The same amount of water is "used" (moved from above lock to below lock) regardless of how many boats of what size are in the lock when it empties or fills.

 

Go and make a drawing showing the state of the (full) lock before the boat enters it, after the boat enters it, after the boat has gone down in the lock, and after the boat has left the lock. The amount of water moved from the upper pound to the lower one -- "used" -- is the same in all cases, it's the drop in water level (the fall of the lock) multiplied by the area of the lock.

 

Archimedes understood this, but it seems that you don't... 😉

Still wrong

Edited December 17, 2023 by peterboat

[magnetman]

The only way that the displacement could alter water usage is if the Boat was craned into the lock. If it goes in and is at all times floating then the water use will stay the same whether it is a canoe or a barge. 

 

The Boat is just a hole in the water. That hole exists as long as the Boat is floating. The fact that the water level does not go up is not relevant. 

 

 

If it was correct that a larger displacement would use less water then there would come a point where a Boat would be large enough to pass through a lock using no water. 

 

I'm sure if this was possible someone would have done it

 

The hole exists whether the lock is full or empty as long as the Boat is floating. If it isn't floating it won't be getting through the lock. 

 

Edited December 17, 2023 by magnetman