Mid-afternoon Brain Teaser

They should be charged less as less water would need to be pumped in to the lock. Unless I'm thinking about it wrong.

I agree. Bigger ships would have greater displacement and thereby need less water.

Doesnt matter, whatever be the ships size, water required to be filled into the lock is the same and besides,the water is filled using gravity feed. hence, both small and larger ships must be charged the same.

You're probably thinking about the AMOUNT of water IN the lock. Larger boats would need more water to keep them floating.. Think about it this way. Boats displace water, so the displacement of a 20' speedboat weighing 2500 lbs would be 2500 lbs of water. A cruise ship displaces around 30,000 tons of water. Think about this simple experiment: say you have an empty swimming pool that is 100' by 50' and is 25' deep (a lock). You put a small rowboat with two people and their fishing gear in the center of the pool (lock). Now, add water until the rowboat just begins to float. You will see that the pool is only a foot deep or so. If you replace the rowboat with a 35'cruiser it will just sit on the bottom until you add more water to cause it to float; then a 70' yacht, etc. I think you get the idea now...

The smaller boats should be charged more. They displace less water and require the pumps to run longer to equalize the water levels across lock gates.

Having used the locks on the Mississippi and Illinois Rivers, I can state:
1) There are no pumps to fill or empty a lock chamber. It's done by gravity and valves. See: http://terrax.org/sailing/locks/canallock.aspx for an example of how the Western Rivers locks (USA) operate. Most other locks are similar.
2) Unless a vessel changes its displacement (or goes aground) during a lockage, the amount of water needed to fill or empty a chamber never changes for the same lift. It's the same even if a chamber is empty. Imagine that you are only transfering the water underneath the vessel, not the water surrounding the vessel.
3) I'm glad I boat in an area where lockages are free, although I'd like to cruise the Trent-Severn waterway for its unusual locks. Go look them up! 8^)

Thanks for the lesson in locks operation. I figured that gravity feed was used when going from upstream to downstream but I thought some sort of pump operation was needed if you were traveling in the opposite direction. ;o)

No pumps are needed. Water is always added from the high side of the lock and drained to the low side of the lock regardless of the direction the boat is traveling, whether is is being lifted or dropped. I agree with everything Madhatter said. Once the locks are closed the amount of water that is drained/added is the same regardless of the size of the vessels traveling through.

A late comment - amount of water used is plan area of lock x difference in water levels, irrespective of presence of or size of boat.

With ref to need for pumps - every operation of the lock uses a flow of water, downhill, naturally. This is fine and the whole system can work by gravity provided there's an adequate supply of water higher up the system, as I'm sure there is on the Mississippi. But there are (or were) canals in UK where there isn't and water has to be pumped back up.

What's unusual about the Severn-Trent (that's what we locals call it, regardless of direction of travel) locks?

Could it be the Mississippi ones that are unusual? ;o)

Most of the locks on the Trent-Severn Waterway National Historic Site of Canada (that's what Parks Canada calls it) are similar to the US Western Rivers locks. In fact, most locks worldwide are of a similar pattern as it's relatively cheap and easy. However, there are a few in the TSWNHSC that are quite different. There are two flight locks, Ranney Falls (11/12) and Healey falls (16/17), two lift locks, Peterborough (21) and Kirkfield (36), and the Big Chute Marine Railway (44). The URL for the Parks Canada page for the TSWNHSC is: http://www.pc.gc.ca/lhn-nhs/on/trentsevern/visit/v isit6_e.asp and one that has better pictures of Big Chute: http://www.edto.net/photo_bigchute.htm. There is a fee for the TSWNHSC, based on boat length and duration of the pass.

I have revealed my ignorance of the geography of Canada.

I thought you were talking about Severn-Trent UK.

Apologies! And thanks for the explanation.

What do you espect from a Canook? They act like they are a real country and almost as good as we are!

This is late, but I found unique "lock". The Falkirk Wheel (Scotland) connects the Forth & Clyde Canal with the Union Canal, at an elevation difference of 115 feet (35 meters). Formerly connected by a flight of 11 conventional locks, removed fron service in 1933, a new (2002) device now connects these waterways.

"Wheel" is about the best description of it - it's NOT your typical means of getting from one waterway to another. 8^)

It's quite a device - go see it.

Their official website is http://www.thefalkirkwheel.co.uk/

I believe the amount of water a boat displaces is irrelevant. If the drop in elevation is 50 feet from the upper reservoir to the lower reservoir, then the volume in the lock @ 50 foot depth has to be transferred each time the level of the lock is raised or lowered. It is the same effort whether the boat is large or small. The same amount of water is transferred.

Not quite . . . Picture a ship which is the shape of the interior of the lock and only one inch smaller in width, length, and depth. For the sake of this illustration, let's agree that the ship floats and has a draft of 10 inches. Let's also use a scaled-down version (so that the calculations are easy) and that the lock is 101 inches long, 51 inches wide, and 25 inches deep, and the ships must be raised 20 inches to get to a higher level. The volume of the lock at the high water mark (20 inches) is 101 X 51 X 20 = 103,020 cubic inches. The volume (displacement) of the ship at its high water mark is 100 X 50 X 10 = 50,000 cubic inches. The amount of water which needs to be pumped in is 53,020 cubic inches. Now, picture a ship which is much smaller and displaces only 5,000 cubic inches of water. The amount of water which has to be pumped in is 98,020 cubic inches.

But with either ship, when it enters the lock at the lower level, it displaces either 50,000 cubic inches or 5,000 cubic inches of water. It will still take 103,020 cubic inches of water to raise it because you have to replace the displacement of the ship at the lower level.

The volume dispalced below the waterline of the vessel does not need to be pumped, so the larger the vessel's displacement, the less water there will be in the lock to pump.

Think of it this way, if no ship was in the lock and the water level must be changed by 50 feet, you would need to pump all of that volume to equalize the locks. If, on the otherhand, we had a ship that was 99% the size and shape of the lock, there would be almost no water in the lock, so you couldn't pump as much water as in the first example.

You are correct. The ship would take up 99% of the volume of the lock and when the water was lowered, it would be sitting on the bottom without enough water to float it out.

Depends on the direction it is going (up or down).

This is hard to explain in just words, but here goes. First of all, the volume of water required to raise a boat from the lower pool level to the upper pool level will be the same for any size boat, no matter the displacement. Because you only need to change the water level, the boat is already floating and displacing water and will displace the same amount of water when it leaves the lock. Suppose that when the boat enters the lock and the gates close the level is at 10 ft, and the upper pool is at 20 ft. As water is added to the lock the deck of the boat rises, and it will rise 10 ft., since the deck is connected to the hull, the bottom of the boat will rise 10 ft. Where was the water added to generate this lift of 10 feet? Underneath the boat, in the volume of the lock that is beneath the hull, a generally rectangular shape of some area and 10 feet in height. The same volume of water that would have to be added if the boat displaced 50 cubic inches or 50,000 cubic inches. Because the water added to generate the lift is not only below the waterline of the boat, it is below the hull of the boat and independent of the displacement of the boat.

Doh! I think you are right!

We're glad you used words, cause we can't see hand signals..

If the water level is the same before and after use the boats should be charged equally because there is no need of pumping or any changes. Simple no?? BTW i tried to login but its not working

Contact the CR4 Admin - send an email to cr4admin@globalspec.com. Those guys are pretty quick to help.

What if a smaller chamber is used to move a smaller boat. The chamber would be smaller ,thus reducing time it took to raise or lower it. The bigger the boat the larger the chamber ,taking more time to fill...I would think time is the cost factor and a smaller boat should also be able to move faster though the lock reducing time again ...Obviously I knowing about locks but thats my theroy

If you neglect the power and time requirements for filling and emptying the locks, they become negligible. The lock will generally take the same time to fill and empty no matter what. The big boats should pay more, simply because when they are in the lock, less vessels will fit in it with them. If it costs $10.00 to go through one cycle at a particular lock, and no one is making a profit, the total income necessary to run the lock is $10.00 per cycle. If only one huge boat can fit in the lock, that boat needs to cough up $10.00 If there are two boats, they each need to cough up $5.00. If boat "A" is twice the size of boat "B", they each still pay $5.00. and so on and so on. The cost of running the lock should be split evenly by the number of boats within it. This would work to the small boats' advantage sometimes, because the small boat can just wait until there are many other small boats. That way, they can split the cost among more vessels

Obviously they should not be charged more because they need more water. They should be charged more because they are bigger and can afford it.

After all, it is commerce!

maybee i dont know anything about locks, but if it has a gate with a body of water on the other side, the water level will equalize when it is open to release the ship and it won't matter.

You would need a heck of a lot more water to transfer a smaller boat. It doesn't displace as much as a larger vessel, requiring more water to bring the lock up to level.