How much extra storage space do you really get WB -v- NB

[Robbo]

3 minutes ago, Machpoint005 said:

^^ Wot he said.

As I said, not everyone understands Archimedes. 

Although when you say Archimedes I keep thinking of the computer!

[Machpoint005]

1 hour ago, mross said:

The larger the boat the less water remains in the lock when the gates are closed.  Therefore less water needs to be drained from the lock to lower the boat to the exit level.  Try and imagine a boat that totally fills a perfectly cubic lock with only enough clearance to move in and out.  It would only take a few gallons to float the boat.  Conversely, a canoe will require almost 100% of the lock's water volume to transit.

If I imagine such a boat there is exactly one lockfull of water difference between a 'full' and an 'empty lock. Do you disagree?

Of course, an 'empty' lock isn't actually empty but that doesn't matter. If your cubic boat just fits into an empty lock, you still have to add one lockfull of water to take the boat to the upper level and float it out. The size of the boat makes no difference at all.

Just now, Robbo said:

Although when you say Archimedes I keep thinking of the computer!

Blimey, that's going back a bit! Was it a principled machine?

[mross]

7 minutes ago, Machpoint005 said:

The size of the boat makes no difference at all.

 

OK, Let's try again.  Consider a lock that holds one hundred tonnes full and twenty tonnes when 'empty' (ie ready to exit at lower level).  A locking with no boat will use eighty tonnes of water.  Agreed?  If a twenty-tonne boat enters the full lock it will displace twenty tonnes of water,  Now a locking will only use sixty tonnes of water.  A widebeam displacing forty tonnes will only use forty tonnes.  

[Robbo]

13 minutes ago, mross said:

OK, Let's try again.  Consider a lock that holds one hundred tonnes full and twenty tonnes when 'empty' (ie ready to exit at lower level).  A locking with no boat will use eighty tonnes of water.  Agreed?  If a twenty-tonne boat enters the full lock it will displace twenty tonnes of water,  Now a locking will only use sixty tonnes of water.  A widebeam displacing forty tonnes will only use forty tonnes.  

Still incorrect, as an empty lock is water + boat weight,  can't use your figures as there isn't enough  water when empty.

empty lock = 50 ton

full lock = 100 ton

 

1 boat,  25 ton

Full lock = 75 ton water 25 ton boat = 100

empty lock = 25ton water, 25 ton boat = 50

amount of water to turn lock 75-25=50 ton

 

another boat, 20 ton.

full lock = 80 ton water, 20 ton boat = 100

empty lock = 30ton water, 20 ton boat = 50

amount of water difference to turn lock  80-30=50 ton

 

[Neil2]

The twenty ton boat is still displacing twenty tons of water when the lock has been emptied.

 

Sorry, Robbo beat me to it and with more detail..

Edited March 23, 2017 by Neil2

[Alan de Enfield]

1 hour ago, Robbo said:

No, Re read it, he said displaces the same weight of water as the weight of the boat.

Ah, yes - I see it now.

44 minutes ago, Robbo said:

Although when you say Archimedes I keep thinking of the computer!

"Screw" that.

[mross]

I was wrong.  The size of the boat does not affect the amount of water used in a locking.  

[Drayke]

3 hours ago, Machpoint005 said:

Which doesn't affect the total volume of water passing through at all - just the rate at which it does so.

If I had two full buckets of water, one with a 25mm hole at the bottom, the other with a 1mm hole at the bottom, the second would take much longer to become empty but the final result would still be two useless empty buckets. 

(Except that Mr Oss has it slightly wrong. The widebeam is heavier so will push the water out of a lock quicker going downhill, but going uphill the locks will fill slower.So swings and roundabouts really... )

That depends on how much you open the sluices.

 

I said it with tongue in check.

[Drayke]

3 hours ago, Machpoint005 said:

Which doesn't affect the total volume of water passing through at all - just the rate at which it does so.

If I had two full buckets of water, one with a 25mm hole at the bottom, the other with a 1mm hole at the bottom, the second would take much longer to become empty but the final result would still be two useless empty buckets. 

Well fix it dear Henry dear Henry fix it.  

[Robbo]

1 minute ago, F DRAYKE said:

(Except that Mr Oss has it slightly wrong. The widebeam is heavier so will push the water out of a lock quicker going downhill, but going uphill the locks will fill slower.So swings and roundabouts really... )

That depends on how much you open the sluices.

 

I said it with tongue in check.

I hope that was reply was in jest, the boat effectively weighs the same as water so it's not heavier than it.  

[Drayke]

4 hours ago, Neil2 said:

 

I agree a nicely proportioned luxemotor or tjalk is a thing of beauty and designed for sailing though I fear we'll be seeing less and less of all wide beams on the network in future as the gap between the bottom and the top decreases every year. 

In which case so will a lot of older narrow boats as there draft is a lot more that widebeams.

[JJPHG]

ok - since my question seems to have been somewhat hijacked I might as well put in my two pennies worth.

The displacement of the water by the boat is proportional to the boats draft displacement and therefore is a function of both it's draft dimensions and the boats total weight (assuming buoyancy).  

My next point is where does the displacement occur?  As the boat enters the lock sure - the water is displaced but its displaced out of the lock (upstream or downstream), as it enters the lock.  Therefore once the lock gates are closed and it becomes essentially a closed system there is no further displacement.  The boat is part of the system (well its draft displacement is if we are just considering the water as the system) and therefore its existence in the lock will have NO effect on the rate at which the lock empties (or fills).  It is not an external force pushing the water out faster.  

However as the volume of water in the lock with the boat in it will be less than when empty (i.e. without a boat in it -because so is taken up by the draft displacement volume) the amount of water in the lock would be less.

So my logic (which I am quite happy to be corrected on) is that a boat with a bigger draft displacement will use less water in the lock.  There is however no real 'saving' of water.  The moment the boat enters the water (or weigh/cargo is added to it) the displacement occurs.  That displacement works its way out of the system at a rate dependent upon the flow of the canal or river

Edited March 23, 2017 by JJPHG
Got it wrong

[JJPHG]

Just another thought.  If we really want to save water should we refrain from locking in winter when the density of the water is at it's greatest!? 

[Machpoint005]

11 hours ago, JJPHG said:

ok - since my question seems to have been somewhat hijacked I might as well put in my two pennies worth.

The displacement of the water by the boat is proportional to the boats draft displacement and therefore is a function of both it's draft dimensions and the boats total weight (assuming buoyancy).  

My next point is where does the displacement occur?  As the boat enters the lock sure - the water is displaced but its displaced out of the lock (upstream or downstream), as it enters the lock.  Therefore once the lock gates are closed and it becomes essentially a closed system there is no further displacement.  The boat is part of the system (well its draft displacement is if we are just considering the water as the system) and therefore its existence in the lock will have NO effect on the rate at which the lock empties (or fills).  It is not an external force pushing the water out faster.  

However as the volume of water in the lock with the boat in it will be less than when empty (i.e. without a boat in it -because so is taken up by the draft displacement volume) the amount of water in the lock would be less.

So my logic (which I am quite happy to be corrected on) is that a boat with a bigger draft displacement will use less water in the lock.  There is however no real 'saving' of water.  The moment the boat enters the water (or weigh/cargo is added to it) the displacement occurs.  That displacement works its way out of the system at a rate dependent upon the flow of the canal or river

You are over-complicating a very simple situation by drawing lines in arbitrary places. Mross now agrees with Robbo, Neil, me, MtB and other (not surprising, since we are all correct).

And thanks to Mross for his gracious admission of a mistake - have a greenie Sir. 

[mross]

1 hour ago, Machpoint005 said:

And thanks to Mross for his gracious admission of a mistake - have a greenie Sir. 

It did hurt!  I was kicking myself!

[Robbo]

46 minutes ago, mross said:

It did hurt!  I was kicking myself!

Well it would hurt if ya kick yourself

Edited March 24, 2017 by Robbo
Spelling

[bargemast]

15 hours ago, mross said:

I was wrong.  The size of the boat does not affect the amount of water used in a locking.  

You were right to admit that you were wrong though.

 

The same mistake is made by many others too, but they often don't want to understand their error.

 

Peter.

[NickF]

I would argue that it is Mike the Boilerman who is wrong ........ the mistake he made was to bring the subject up in the first place as it always results in a discussion similar to the above and no one ever agrees. Therefore Mike the Boilerman is wrong but I suspect he did it on purpose!

[Bewildered]

On 24 March 2017 at 14:16, NickF said:

I suspect he did it on purpose!

Introducing dolphins to a lock isn't going to affect the displacement or the speed they fill and empty 

[WotEver]

8 minutes ago, Bewildered said:

Introducing dolphins to a lock isn't going to affect the displacement or the speed they fill and empty 

Besides, they never ever help with the paddles. 

[Trillian]

13 hours ago, WotEver said:

Besides, they never ever help with the paddles. 

They do however distract the onlookers who then don't notice me make a right mess of things!

[Bewildered]

so long, and thanks for all the fish!