Well, what is fair then?

[Gibbo]

I think I've cracked it for you. The volume of water that the boat displaces doesn't move out of the lock when the boat goes in. The level in the lock and the pound above goes up very slightly - a fraction of a mm as the water finds its own level. Local water swirls make it look as if it's coming out - but it isn't. It simpy can't, otherwise the water would have a slope.

 

But the change in water volume in the lock chamber from full (witha boat in) to empty (with a boat in) remains exactly the same. And it's exactly the same if there is no boat at all. and this is true in either direction.

 

Are you having a laugh?

 

Please tell me you are.

 

Gibbo

[Machpoint005]

Of course. But I think I've found the flaw in your (otherwise quite logical) reasoning.

Edited November 29, 2008 by Machpoint005

[Gibbo]

How can it possibly be otherwise, if the same amount of water goes through the paddles? The amount of water actually in the lock (before or after) is irrelevant.

 

Because................

 

Assume (going down a lock) 10,000 gallons goes through the paddles. The bottom pound now has 10,000 gallons more in it. When the boat comes out of the lock, a volume of water equal to the displacement of the vessel goes from the pound back into the lock. The bottom pound now contains 10,000 gallons more MINUS the displacement volume less.

 

I know you seem to think that water doesn't swap between the lock and the pound when the boat moves out but that is where your mistake lies.

 

Gibbo

[US Marines]

Well I still do NOT agree and my last maths (late last night/this morning!!) showed why.

 

If you believe that boats magically appear on the canal, having moved no water about previously, then of course I agree that the bigger the boat the bigger the "V3" pushed back into the pound (well I agree this bit anyway) when the boat enters the lock and there will be a net V3 - V3' between the boats at that lock after the whole locking operation is finished.

 

But you are all (well most) seeing the "King's suit of clothes" because boats DON'T magically appear on the canal - they were originally craned in (etc) and have reached their present position by traversing locks where their size made absolutely no difference to the water used.

 

As I said in my last posts, if I cruise up to the next lock, I push an amount equal to my displacement back into the pound. The pound's volume increases due to my size. A widebeam, which I am not, will push maybe 50% more back into the pound so our size does make a difference "at that instant in time".

 

However, we both got to that lock by traversing the previous lock, where the widebeam caused 50% more water than my boat to flow OUT of the pound back into the lock and so restoring the balance again.

 

Gibbo is suggesting that if I go down 100 locks, I will cause an additional usage of water of 100 x my V3 which will be around 1400 tons of additional water and that a widebeam, on the same trip, will use an additional 100 x maybe 23 tons = 2300 tons of water. Thus, the widebeam, will have caused an additional usage of 900 tons of water, compared to my boat.

 

This is nonsense.....what I give to the pound on entering a lock, due to my displacement, I originally took away when I entered the pound from the previous lock. There will be no net difference between the boats on such a journey or indeed any journey.

 

Chris

 

I can't (and won't!) speak for Gibbo and what he was saying but I agree with you Chris - and I always have - the only 'permanent' effect on the volume of water in the total system occurred when the boat was first craned in - ever since that point in time, the 'hole' it made in the water then has just been moving around the network.

 

Even this 'permanent' effect isn't really permanent because the boat will eventually be removed from the water, and the downstream flow and the management of the water levels will combine to soon fill up the 'hole' it made when it was in the water.

 

Brilliant - it really is good when we all agree !

 

 

 

Now - [tin hat on and running for cover fast] - the title of this thread is about 'fairness' in licensing fees - what's the answer to that then ?

 

 

Edited to add: Oh God - whilst I was typing this post, other stuff has obviously happened - I'll be leaving it to you guys now.

Edited November 29, 2008 by US Marines

[Machpoint005]

USM - dead right.

If water flows out at one end, it comes back at the other end, and there is no net change. That is the point. Misapprehensions occur when an intermediate (non-stable) condition is assumed to be stable.

[chris w]

The debate re water usage (as opposed to the OP's question!!!!!!!!!!) is whether a larger boat uses more water traversing a lock than a smaller boat. If a boat were to magically appear in a puff of smoke in the pound before the lock and enter the lock, then the larger magic boat will push more water back into the pound than the smaller magic boat.

 

However, being magic boats, they did not have to enter the pound from the previous lock and so did not remove the same amount of water from the pound as occurs in real life.

 

Chris

[Gibbo]

I think I've cracked it for you. The volume of water that the boat displaces doesn't move out of the lock when the boat goes in.

 

Do you honestly believe this?

 

Where does it go then. It was in the lock before the boat went in. Once the boat has gone into the lock it is no longer there. It can't be. There's a bloody boat in the way!

 

The level in the lock and the pound above goes up very slightly - a fraction of a mm as the water finds its own level. Local water swirls make it look as if it's coming out - but it isn't. It simpy can't, otherwise the water would have a slope.

 

Again do you really believe this or are you having a laugh.

 

The boat is already in the pound, the gates are open. Moving the boat into the lock CANNOT alter the level in the pound or the lock.

 

Gibbo

[chris w]

On this point, I absolutely agree with Gibbo, that an amount equal to V3 (the boat's displacement) moves out of the lock as you enter it and so increases the pound's volume JUST AS when I entered the pound from the previous lock, I caused the same amount V3 to flow OUT of the pound, into the previous lock, thus decreasing the pound's volume. ie: net change to pound due to the boat's displacement = zero.

 

Chris

Edited November 29, 2008 by chris w

[Machpoint005]

OK consider this, then. When the lock is full, it's part of the top pound.

When the lock is empty, it's part of the bottom pound.

Movement of water into or out of the bit we call the lock is irrelevant.

I'ts only when the gates are closed and water starts to flow through the paddles that the situation changes. Anything before this starts is irrelevant. Anything after the water stops flowing and the gates can be opened is irrelevant. The volume of water goes down by exactly one lockful in the top pound, and goes up by exactly one lockful in the borrom pound, and all the net movement of water is through the paddles.

The calculation doesn't start until we start to shift water about, and the 'lockful' is the cuboid of water bounded by the lock walls, the lock gates, the lower level (ie level with the lower pound) and the upper level (ie level with the upper pound). This is the only way in which we can satisfy the laws of physics, and must therefore be correct.

[US Marines]

Oh no - here I go again (and I said I wouldn't too !)

 

I don't think anyone is disputing what you say in your post directly above this one Machpoint.

 

However......

 

Because a boat displaces water, when its upstream of the bottom lock gates, there is a boat sized 'hole' in the water in the top pound that, when the boat moves downstream of the bottom gates, is 'backfilled' from the bottom pound. Therefore, when you just look at the effect of one downhill locking manoeuvre in isolation, taking a boat through the lock causes less nett water to flow into the bottom pound than if you went through the same locking cycle without a boat in the lock - because, in that case, there is no boat sized 'hole' in the top pound to backfill.

 

This effect is bigger with a heavy boat than a light boat and, compared to the overall amount of water that flows into the bottom pound from the top pound during a locking cycle, it is small. But it does still exist.

Edited November 29, 2008 by US Marines

[Pretty Funked Up]

http://jasonwilsondesign.com/rubbish/locksim.html

 

Nice little demonstration, could you adjust the figures at the top so they only include water? (not the boat as well)

[Jason Wilson and Family]

Nice little demonstration, could you adjust the figures at the top so they only include water? (not the boat as well)

 

I could... but it wouldn't make much difference. As people are STILL arguing it's clear that there's not goign to be any change in opinions no matter how wrong.

[Machpoint005]

Oh no - here I go again (and I said I wouldn't too !)

 

I don't think anyone is disputing what you say here Machpoint.

 

However......

 

Because a boat displaces water, when its upstream of the bottom lock gates, there is a boat sized 'hole' in the water in the top pound that, when the boat moves downstream of the bottom gates, is 'backfilled' from the bottom pound. Therefore, when you just look at the effect of one downhill locking manoeuvre in isolation, taking a boat through the lock causes less nett water to flow into the bottom pound than if you went through the same downhill locking cycle without a boat in the lock - because, in that case, there is no boat sized 'hole' in the top pound to backfill.

 

Are you sure about that? Think of my frozen lockfull, with a dip in the top and a lump in the bottom. What matters is what happens between the time the top gates close and the bottom gates open. Before and after those two key events, nothing happens (there is no flow through the lock!)

 

This effect is bigger with a heavy boat than a light boat and, compared to the overall amount of water that flows into the bottom pound from the top pound during a locking cycle, it is small. But it does still exist.

It is negligible. The displacement volume of a boat is several orders of magnitude smaller than the volume in the pound. Even if locks are in a flight (or a staircase) the water use is one average lockful of water going from top to bottom, and one average lockfull of water when going from bottom to top. I say 'average' because no two locks in a flight are exactly the same size. But the average lockful is completely independent of the displacement of the boat. Unless the displacement is so great that extra water flows over the by-pass weir. But that wasn't the argument.

 

I think we are all agreeing, but we don't realise it.

[wonderdust]

Are you sure about that? Think of my frozen lockfull, with a dip in the top and a lump in the bottom.

 

But you dont get a lump in the bottom!

[OptedOut]

I think the flight bottom backpump would have cut in by now.

[Machpoint005]

But you dont get a lump in the bottom!

Yes, you do. It's the space that had the boat in it, when the boat has gone. The 'empty' lock still has water in it, and the water in the empty lock has a dip in the top.

[US Marines]

Are you sure about that? Think of my frozen lockfull, with a dip in the top and a lump in the bottom. What matters is what happens between the time the top gates close and the bottom gates open. Before and after those two key events, nothing happens (there is no flow through the lock!)

Yes.

 

You can't pass a boat through a frozen lock. A lock is no different to any other part of the system, when you move your boat forward through the water, the 'hole' left behind it is mostly backfilled from in front of it (completely backfilled when travelling upstream). If you did manage to succeed in locking a boat across solid ice, the boat would leave a hole in the top pound and sit on top of the ice in the bottom pound. If all the ice was then melted, the top pound's level would be slightly lower (until it was replenished by downstream flow) and the bottom pound's level would be slightly higher (until it decreased by downstream flow and the management of the water level (by weirs etc) re-establishing dynamic equilibrium).

 

I repeat, this 'frozen' example is not relevant to reality because the liquid water flows backwards through pressure differences to maintain its level.

 

It is negligible. The displacement volume of a boat is several orders of magnitude smaller than the volume in the pound.

I did say it was small !

 

I think we are all agreeing, but we don't realise it.

We all realised it a little while ago - not sure that you did though !

Edited November 29, 2008 by US Marines

[Dominic M]

OK consider this, then. When the lock is full, it's part of the top pound.

When the lock is empty, it's part of the bottom pound.

Effectively, yes. When the boat enters it will displace its own weight and that body of water can only go one way - through the open gates behind it. But then it's being doing that all the time the boat has been moving along the pound - many will be aware of how a boat coming past on the canal is pushing water past creating a brief level change that then stabilises as water rushes to fill the "hole" left by the boat.. Your visualisation of what then happens next once the locks gates are closed, be it travelling uphill or down, explains it perfectly. Whilst a heavier boat will mean less water in the lock the lock still has to make level, and when the boat leaves the lock and equal amount of water as that displaced when it entered has to fill the "hole" left by the boat. The weight of boat is irrelevant - the higher pound will lose the same amount of water whichever direction the boat is going in and that amount will be equal to the lock chamber's capacity, less the amount always retained below the lower cill level. This is precisely what Chrisw's maths explained when he launched his V2 stuff. The fact that the operation of one lock has been used to try and get this across has been for simplicity, but it is the same if the boat passes through 100 locks.

 

I can see there is not going to be agreement on this but nothing will convince me otherwise. Any other contrary belief involves scrapping the laws of physics as we know them.

[US Marines]

I can see there is not going to be agreement on this but nothing will convince me otherwise. Any other contrary belief involves scrapping the laws of physics as we know them.

Dominic - I actually think that we do all now agree ! (even perhaps Machpoint now ?)

 

There is only one boat sized 'hole' and this moves with the boat. The only effect caused by a boat on the volume of water in the system as a whole was made when the boat was first craned into it, and this effect will remain until the boat is removed from the system.

 

The effect of the boat's position within the system at any one time is only to displace some water out of the pound it is currently in, back into the pound it last came from.

 

Weird though it may seem at first, this includes backfilling apparently 'uphill' through a lock (though, of course, because of the way a lock works, the backfilling water does not move backwards up the height of the fall of the lock).

Edited November 29, 2008 by US Marines

[Dominic M]

Dominic - I actually think that we do all now agree ! (even perhaps Machpoint now ?)

 

There is only one boat sized 'hole' and this moves with the boat. The only effect caused by a boat on the volume of water in the system as a whole was made when the boat was first craned into it, and this effect will remain until the boat is removed from the system.

 

The effect of the boat's position within the system at any one time, is only to displace some water out of the pound it is currently in, back into the pound it last came from.

 

Weird though it may seem at first, this includes backfilling apparently 'uphill' through a lock (though, of course, because of the way a lock works, the backfilling water does not move backwards up the height of the fall of the lock).

Well, I think a number of us agree - including Machpoint005 who had it right from the start (although I couldn't quite see his later idea that the water didn't get pushed out of the lock through the open gates when the boat entered - but if you read what he stated overall then he has sided firmly with Archimedes. Pity he doesn't get to post on this forum. How's your classical Greek ?).

Edited November 29, 2008 by Dominic M

[Gibbo]

I don't know why I'm bothering but here goes anyway........

 

Well, I think a number of us agree - including Machpoint005 who had it right from the start.......................

 

Well he didn't did he.

 

This is what he said.................

 

Fill an empty lock - no boat in it. You have put in a cuboidal 'block of water'.

Empty the lock - no boat in it. You have got rid of a cuboidal block of water.

 

That bit is correct. He went on to say...........

 

Now put a boat in - any boat. Fill the lock. You have put in a cuboidal block of water with a boat shaped depression in the top. You started with a flat surface with a boat-shaped depression in it, and finished with one. However, the imaginary block has a depression in the top and a lump on the bottom!

 

That bit is incorrect. The "lump on the bottom" stays in the top pound. It does not move down to the lower pound.

 

Therefore in the case of this one single lock, less water is moved down to the lower pound than with no boat in the lock.

 

Gibbo

[Pretty Funked Up]

What happens if the wind is blowing from the east?

 

 

sorry couldnt resist

[US Marines]

What happens if the wind is blowing from the east?

 

 

sorry couldnt resist

 

At this time of year we get bleeding cold !

 

BW should put all their wind generators on the eastern side of the country, so its the coldest winds that they slow down....

 

 

Actually, now I think about it - its not fair - those boaters on the west side of the country get milder weather and lots of rain compared to those on the east side, who get more temperature extremes (both hot and cold) and more droughts.

 

I think these differences should be reflected in the licence fees.....it is simply indisputable that these factors affect the number of potentially enjoyable cruising days in each region, as well as water usage.

 

(and now it becomes clear that the thread about (apparently) appalling weather in Yorkshire is a blatant attempt to sway the numbers in their favour ! )

Edited November 29, 2008 by US Marines

[Machpoint005]

I don't know why I'm bothering but here goes anyway........

 

 

 

Well he didn't did he.

 

This is what he said.................

 

 

 

That bit is correct. He went on to say...........

 

 

 

That bit is incorrect. The "lump on the bottom" stays in the top pound. It does not move down to the lower pound.

 

Therefore in the case of this one single lock, less water is moved down to the lower pound than with no boat in the lock.

 

Gibbo

We nearly all agree, and have done for some time. However, someone doesn't get it. And someone else needs to be able to distinguish between an analogy and a literal description.

And one of these two somebodies doesn't understand my sense of humour. Can't blame him for that.

 

BUT: How can the lump on the bottom (my unfortunate phrase) stay at the top when the boat is still floating in the bottom of the lock? Are we sure we are all talking about the same lump, or shall I draw a diagram?

 

Res ipsa loquitur, I say.

[Gibbo]

We nearly all agree, and have done for some time. However, someone doesn't get it. And someone else needs to be able to distinguish between an analogy and a literal description.

And one of these two somebodies doesn't understand my sense of humour. Can't blame him for that.

 

BUT: How can the lump on the bottom (my unfortunate phrase) stay at the top when the boat is still floating in the bottom of the lock? Are we sure we are all talking about the same lump, or shall I draw a diagram?

 

Res ipsa loquitur, I say.

 

There isn't a lump on the bottom. That's your phrase (it's not unfortunate, I quite like it, it's descriptive). What you perceive to be a lump on the bottom is a lump of water that stays in the top pound.

 

Gibbo