Leaving gates open

[mayalld]

 

 

And that reason is?

 

Before you answer, there are signs on two locks at Wootton Rivers instructing boaters to leave the lock EMPTY and with lower paddles OPEN "to prevent draining of the pound".

 

I can't figure out how that would help but CRT know better than me. There are also locks in the Crofton flight bearing similar instructions but not giving a reason.

 

OK, I can suggest a possibility.

 

With the lock empty, the top gate makes the best possible seal that it can. With a part full lock, as the level rises part way up the top gate, the seal on the top gate becomes less secure.

 

So, if you empty the lock, and make sure it stays empty, the leakage through the top gate is less. If the lock is left full or nearly full, more water can pass through the top gate.

 

This can end up with a situation where the lock is about 9 inches down, leaking through the walls, and with almost no seal on the top gate topping itself up, and emptying the pound above.

[Dave_P]

 

 

And that reason is?

 

Before you answer, there are signs on two locks at Wootton Rivers instructing boaters to leave the lock EMPTY and with lower paddles OPEN "to prevent draining of the pound".

 

I can't figure out how that would help but CRT know better than me. There are also locks in the Crofton flight bearing similar instructions but not giving a reason.

Where there is a sign asking that a lock is left empty and open, the most obvious explanation is that there's a leak from within the lock and the top gates aren't balanced properly so they swing open when the lock is full. This would lead to the pound above draining. It's a unusual and specific circumstance so that's why CRT put the sign up. The exception proves the rule. Where there is no sign - shut the gates.

[Tacet]

 

 

Also, it is currently selfish and lazy if you leave gates open while almost everyone else closes them. This mean you get the 50/50 chance of the lock being in your favour, you almost never have to close a gate when it's not in your favour but then also never bother to shut a gate behind you. This means that you will average less work per lock by encumbering other boats with additional work. If you can't understand the maths behind this, then I can't really help you any further.

 

Well, I'll admit to not understanding the maths on the underlined bit. Assuming equal number of boats following and opposing you, some will have more work and some less, i.e. no net difference.

 

Dealing only with the effort and efficiency of lock working (i.e. putting aside water saving and people-drowning in-locks type issues), it is overall less work to leave gates open on leaving. If a boat next comes the opposite way, it is less work (gates are not needlessly closed only to be re-opened) and if a boat follows in the same direction, the subsequent boat only has to do what you didn't (i..e close the gates). Whilst "they have to do it rather than "you", "they" save the equivalent effort by not closing-up on departure and so-on.

 

Add in that it is less faff to close the left-open gates when you are lock-working anyway (i.e. turning the lock) than to do so either on arrival to a lock ostensibly in one's favour or on departure, both of which require someone to be put/collected from the bank other than in a close flight. Add-in lost levels due to minor leakage and the argument is more compelling.

[nicknorman]

In practice, top gates do generally leak less than bottom gates, but that's mainly down to them being smaller and lighter, and distorting less.

The hydrostatic pressure on bottom gates is far greater than at the top end, . . . . there's the the rise/fall of the lock plus the depth over the cill adding up to the head of water against the bottom gates, . . . at the top end there's only the depth over the cill.

Usually you are right on this sort of thing Tony, but in this case completely wrong. The pressure is due only to the level difference across the gate, nothing to do with how much depth of water below / depth of the gate below the lower level.

[Tam & Di]

 

Also, it is currently selfish and lazy if you leave gates open while almost everyone else closes them. This mean you get the 50/50 chance of the lock being in your favour, you almost never have to close a gate when it's not in your favour but then also never bother to shut a gate behind you. This means that you will average less work per lock by encumbering other boats with additional work. If you can't understand the maths behind this, then I can't really help you any further.

 

There's something I just can't understand about what you are saying here, maths notwithstanding. The "you" presumably means the "leave gates open" person. When following another boat the locks are never in his favour, but if "you" is following a person who is closing all gates behind him then he is saved the work of closing them himself when preparing the lock for his own use. He does however have to check that the "closer" has shut the paddles properly as they are often left partially open, so it only saves small effort. When "you" meets craft travelling in the opposite direction it would only then be 50/50 chance if everyone was a "leave gates open" person, but if the majority close gates on leaving "you" will never have a lock in his favour in that direction either. So "you"s odds are far less than 50/50. Put simply, the odds against ever finding a lock in your favour if gates are always shut by the previous user are 100%, unless meeting a craft in the opposite direction who sees you coming and is not mindless.

 

Tam

[Paul C]

 

There's something I just can't understand about what you are saying here, maths notwithstanding. The "you" presumably means the "leave gates open" person. When following another boat the locks are never in his favour, but if "you" is following a person who is closing all gates behind him then he is saved the work of closing them himself when preparing the lock for his own use. He does however have to check that the "closer" has shut the paddles properly as they are often left partially open, so it only saves small effort. When "you" meets craft travelling in the opposite direction it would only then be 50/50 chance if everyone was a "leave gates open" person, but if the majority close gates on leaving "you" will never have a lock in his favour in that direction either. So "you"s odds are far less than 50/50. Put simply, the odds against ever finding a lock in your favour if gates are always shut by the previous user are 100%, unless meeting a craft in the opposite direction who sees you coming and is not mindless.

 

Tam

 

It would be 100% chance for the oncoming boater.

 

If gates are left open, the chance of it being set for the next boater is 100% if they're coming the opposite direction; and 0% if same direction (ie following you). If you assume equal traffic and equal spacing (which doesn't really hold true) it could be averaged out at 50%.

 

If gates are not left open, there's a good chance the lock will part fill or part drain, so the chance of it set is, overall, much less than 50%. And the gates would need to be opened (going down) anyway, thus requiring a stop to do so.

[mayalld]

 

There's something I just can't understand about what you are saying here, maths notwithstanding. The "you" presumably means the "leave gates open" person. When following another boat the locks are never in his favour, but if "you" is following a person who is closing all gates behind him then he is saved the work of closing them himself when preparing the lock for his own use. He does however have to check that the "closer" has shut the paddles properly as they are often left partially open, so it only saves small effort. When "you" meets craft travelling in the opposite direction it would only then be 50/50 chance if everyone was a "leave gates open" person, but if the majority close gates on leaving "you" will never have a lock in his favour in that direction either. So "you"s odds are far less than 50/50. Put simply, the odds against ever finding a lock in your favour if gates are always shut by the previous user are 100%, unless meeting a craft in the opposite direction who sees you coming and is not mindless.

 

Tam

 

The maths are fairly simple.

 

If we exclude the case where an approaching boat from the other direction can be seen (in which case we are all agreed that gates should be left open), and consider the case where everybody leaves a lock not knowing whether the next boat will be coming the same way or the opposite way.

 

Let us also not consider the various moves along the lock, and consider instead just the number of times the gates must be operated.

 

There are effectively two different regimes - "Close 'em up" and "leave 'em open", so we need to consider 4 different cases;

 

1) The rule is "close", and all boaters follow the rule

2) The rule is "close", and a single boater doesn't follow the rule

3) The rule is "open", and all boaters follow the rule

4) The rule is "open" and a single boater doesn't follow the rule.

 

Case 1 is the current situation, and it has a satisfying degree of equality.

All boaters have exactly 4 gate operation operations to perform.

 

Case 2 is the current situation, but with some people arbitrarily deciding to change the rules that apply to them.

It works well for the maverick, because he will always save one gate operation, and will have to operate a gate 3 times.

The following boater (following the rules) will have either 3 or 5 gate operations, so may lose out, but on average will not.

 

Case 3 is the sunlit uplands of what will happen if all leaks are fixed, and we move to "leave 'em open"

If you arrive at a lock set for you, you will have just 2 gate operations, a distinct saving.

If you arrive at a gate set against you, you will have 4 gate operations, no more than now.

 

Case 4 is the same, but some people will cling to what they know

The rebels will have 3-5 gate operations.

The conformers following a rebel will have 3 gate operations.

 

So, the upshot is;

 

If the underlying reasons for closing gates was fixed, it would make life easier for all if we left gates open when no other boats could be seen. Individuals adopting this practice gain for themselves, but may cause extra work for those who follow the rules.

 

For the time being, the reasons for shutting gates hold sway, notwithstanding the time and motion analysis above.

[Tony Dunkley]

Usually you are right on this sort of thing Tony, but in this case completely wrong. The pressure is due only to the level difference across the gate, nothing to do with how much depth of water below / depth of the gate below the lower level.

 

I'm right with this as well. The pressure head on the bottom gates when the lock is full of water to the top level is greater than the pressure head on the top gate with the water in the chamber at the lower level, except at the relatively few locks where the rise/fall of the lock is equal to or less than the depth over the top cill.

[Tony Dunkley]

 

The maths are fairly simple.

 

 

The whole matter is very simple, and there's no need for any maths or any other sort of theoretical analysis.

 

If everybody closes up behind their boat at every lock, regardless of whether or not there is any point in doing so, then nobody will ever have a lock ready, . . . . that's a 100% certainty.

 

If everybody leaves the gates open, when there is no serious leakage at the other end and therefore no point in closing them, then there's a 50 /50 chance that the next boat to come along will find the lock ready.

[Dave_P]

Usually you are right on this sort of thing Tony, but in this case completely wrong. The pressure is due only to the level difference across the gate, nothing to do with how much depth of water below / depth of the gate below the lower level.

I thought the same, but didn't dare say!

 

There's something I just can't understand about what you are saying here, maths notwithstanding. The "you" presumably means the "leave gates open" person. When following another boat the locks are never in his favour, but if "you" is following a person who is closing all gates behind him then he is saved the work of closing them himself when preparing the lock for his own use. He does however have to check that the "closer" has shut the paddles properly as they are often left partially open, so it only saves small effort. When "you" meets craft travelling in the opposite direction it would only then be 50/50 chance if everyone was a "leave gates open" person, but if the majority close gates on leaving "you" will never have a lock in his favour in that direction either. So "you"s odds are far less than 50/50. Put simply, the odds against ever finding a lock in your favour if gates are always shut by the previous user are 100%, unless meeting a craft in the opposite direction who sees you coming and is not mindless.

 

Tam

By, 'in your favour' I mean't either full or empty. Not whether the gates are open or closed. Does that help?

[nicknorman]

I'm right with this as well. The pressure head on the bottom gates when the lock is full of water to the top level is greater than the pressure head on the top gate with the water in the chamber at the lower level, except at the relatively few locks where the rise/fall of the lock is equal to or less than the depth over the top cill.

Ok I take the point for locks where the cill is exposed when the lock is empty. As you say, most but not all.

I thought the same, but didn't dare say!

 

You were lucky then! But he was only correct for some locks.

[Dave_P]

 

It would be 100% chance for the oncoming boater.

 

If gates are left open, the chance of it being set for the next boater is 100% if they're coming the opposite direction; and 0% if same direction (ie following you). If you assume equal traffic and equal spacing (which doesn't really hold true) it could be averaged out at 50%.

 

If gates are not left open, there's a good chance the lock will part fill or part drain, so the chance of it set is, overall, much less than 50%. And the gates would need to be opened (going down) anyway, thus requiring a stop to do so.

This is quite right, but if the lock is part filling or part draining then it is definitely leaking, so closing both ends is necessary to save water.

[Bewildered]

Ok then what is the correct procedure when after using a lock you close the gates,happily cruise off, and then happen to glance over your shoulder to find that the gates have opened of their own accord?

Do you

a.) moor up, return to the lock, shut the gate again, and add or remove water necessary to hold gate in place

Or

b.) think, sod it, I've closed them once and complied with the rules, and just keep cruising

Edited September 1, 2016 by Bewildered

[nicknorman]

Ok then what is the correct procedure when after using a lock you close the gates,happily cruise off, and then happen to glance over your shoulder to find that the gates have opened of their own accord?

Do you

A) moor up, return to the lock, shut the gate again, and add or remove water necessary to hold gate in place

Or

think, sod it, I've closed them once and complied with the rules, and just keep cruising

Generally the latter. Some gates are badly-hinged and will always swing open. Quite a few like that on the S Stratford we've just done. If the other gate were leaking badly the gate would be kept closed.

[MtB]

Ok then what is the correct procedure when after using a lock you close the gates,happily cruise off, and then happen to glance over your shoulder to find that the gates have opened of their own accord?

Do you

a.) moor up, return to the lock, shut the gate again, and add or remove water necessary to hold gate in place

Or

b.) think, sod it, I've closed them once and complied with the rules, and just keep cruising

 

 

The latter.

 

And if you meet a boat coming the other way who will know you left it open when he gets there, instead of feeling faintly sheepish as you pass, cheerily shout "I've left a gate open for you at the lock as I knew you were coming!"

[billS]

When single handing the locks left open option is even more attractive.

 

On a fully closed lock you have to get off the boat outside the lock to open and close the gates twice per lock -every lock

 

In the left open scenario, it is only on average once every two locks - a saving of 75%.

[Tam & Di]

 

By, 'in your favour' I mean't either full or empty. Not whether the gates are open or closed. Does that help?

 

That does explain your statement, but it also demonstrates that you are wrong. Tony has alread said the same in far fewer words, arriving at a lock where the gates are closed at either end means you must stop and someone gets off before you can go into the lock - 100% of locks are against you.

 

To put it another way if it is simpler, a lock can only be said to be ready in your favour if you can motor in without waiting first.

 

Tam

Edited September 1, 2016 by Tam & Di

[Tony Dunkley]

But he was only correct for some most locks.

 

I've corrected that for you, Nick.

[nicknorman]

The latter.

 

And if you meet a boat coming the other way who will know you left it open when he gets there, instead of feeling faintly sheepish as you pass, cheerily shout "I've left a gate open for you at the lock as I knew you were coming!"

The exception being if you have a following boat, then I'd want to make sure the gates were closed and whilst your at it, might as well open a paddle for them.

[john6767]

You lot should try the Nene, leave the bottom guillotine up which every way you are travelling, what a pain.

 

At least the few locks on the Nene that are mitre gates both ends are leave the exit gates open, as of course you do on all the locks on the Avon for example.

 

I assume there are specific reasons for the guillotine case, but on a river you would have thought the leaving exit gates open would always be the way, but it is not, the Thames for example, you close the gates behind you.

[FadeToScarlet]

You lot should try the Nene, leave the bottom guillotine up which every way you are travelling, what a pain.

 

At least the few locks on the Nene that are mitre gates both ends are leave the exit gates open, as of course you do on all the locks on the Avon for example.

 

I assume there are specific reasons for the guillotine case, but on a river you would have thought the leaving exit gates open would always be the way, but it is not, the Thames for example, you close the gates behind you.

Absolute worst case scenario is following someone upriver who isn't following the rule, so you have to work each lock (and they are heavy and awkward) three times, rather than just twice.

 

Best case scenario is someone arriving to go downstream as you're in the lock going upstream, so only one lock operation.

 

Idyllic scenario is sharing with Alan on Bletchley who sends his son ahead (or he goes himself) to lockwheel by bike, which really speeds things up!

[nicknorman]

You lot should try the Nene, leave the bottom guillotine up which every way you are travelling, what a pain.

At least the few locks on the Nene that are mitre gates both ends are leave the exit gates open, as of course you do on all the locks on the Avon for example.

I assume there are specific reasons for the guillotine case, but on a river you would have thought the leaving exit gates open would always be the way, but it is not, the Thames for example, you close the gates behind you.

For the nene it's because the closed guillotine is a barrier to flood water. Whereas with the guillotine open, water can flow over the top gates without flooding the lock side, therefore assisting the weirs and sluices in times of high flow.

[john6767]

Absolute worst case scenario is following someone upriver who isn't following the rule, so you have to work each lock (and they are heavy and awkward) three times, rather than just twice.

Best case scenario is someone arriving to go downstream as you're in the lock going upstream, so only one lock operation.

Idyllic scenario is sharing with Alan on Bletchley who sends his son ahead (or he goes himself) to lockwheel by bike, which really speeds things up!

I agree, when going up and a boat appears going down you feel like you have won the lottery!

For the nene it's because the closed guillotine is a barrier to flood water. Whereas with the guillotine open, water can flow over the top gates without flooding the lock side, therefore assisting the weirs and sluices in times of high flow.

If it is in flood perhaps, but than you should not be on the river. The top of the guillotine is always much lower than the lock side, as is the top of the top gates, I can't see how you could flood the lock side.

[FadeToScarlet]

For the nene it's because the closed guillotine is a barrier to flood water. Whereas with the guillotine open, water can flow over the top gates without flooding the lock side, therefore assisting the weirs and sluices in times of high flow.

Not so much flood water, just normal flow.

 

The topgates were designed to assist the weirs with the flow over them. Because the guillotine gates are higher than the topgates, leaving that closed will muck up the level on that particular reach of the river.

 

However, the EA have added planks to a lot of them to lessen the flow (e.g. Titchmarsh) and there is a lot of debate locally about whether that's good or bad.

[GUMPY]

You lot should try the Nene, leave the bottom guillotine up which every way you are travelling, what a pain.

 

At least the few locks on the Nene that are mitre gates both ends are leave the exit gates open, as of course you do on all the locks on the Avon for example.

 

I assume there are specific reasons for the guillotine case, but on a river you would have thought the leaving exit gates open would always be the way, but it is not, the Thames for example, you close the gates behind you.

Nene is because the top gates act as a weir, wont happen with guillotine as its to high.

Being really picky Thames locks should be left with all gates closed and empty