Panama Canal Question

[DefinitelyMe]

To answer the OP's question. Our advisor explained this to us.

For both sets of locks, the ship we were with was maxed out on draught and beam, so when it's coming into or going out of a lock the hardest part is forcing the water around and underneath the ship and out of the lock. So as the ship comes in it pushes water ahead of it and when it goes out it's trying to suck water from forward and push it back to fill in the space behind it. Apparently, during these maneuvers the ship's engines will often be full ahead. Make sense?

Going in is always a little easier than going out, because going in the water rises (by a LOT!) and then spills over through the overflow ports into the next section. But going out there's nowhere for the water to come from except in front of the ship.

So, the first set of locks you're going up, which means that the ship comes in shallow but has an easy time leaving because it can suck water under the keel. It makes sense to have small boats behind because the ship has a pretty easy time and doesn't need to be going full ahead to get out of the lock, but might run into the small boats if they were ahead.

But in the second set of locks it's much harder because the depth under keel is virtually nil as the ships are coming out of the locks. They are full ahead and ours still took about 15 minutes just to get out of the lock. So you want the small boats ahead. They can scurry off as soon as the lock doors open and be tied up in the next one ready to go when the ship finally gets there.

There's one other thing - in the penultimate lock, the lock doors open and all the salt water in the last lock mixes with the fresh water in the penultimate one. Because salt water is more dense it goes under the layer of fresh, and the fresh water (along with anything floating on it) rushes forward. This is by far the most dangerous lock for small boats, which often end up spinning around all over the place or being slammed into the (closed) lock doors at the other end. They would rather have yachts hitting the lock doors than a ship, which is what would happen if the yachts were behind.

This is how our advisor basically explained it and it makes sense to me. Cool eh?

[Jim Woodall]

DefinitelyMe:

Excellent Explanation!!

It makes lots of sense, thank you so much for explaining this. I asked several people who have transited the canal and no one knew the reason.

[Lodesman]

Originally Posted by DefinitelyMe

There's one other thing - in the penultimate lock, the lock doors open and all the salt water in the last lock mixes with the fresh water in the penultimate one. Because salt water is more dense it goes under the layer of fresh, and the fresh water (along with anything floating on it) rushes forward. This is by far the most dangerous lock for small boats, which often end up spinning around all over the place or being slammed into the (closed) lock doors at the other end. They would rather have yachts hitting the lock doors than a ship, which is what would happen if the yachts were behind.

I like the rest of your explanation, but this part doesn't make sense. The locks are filled by freshwater. The final (lowest, ocean-side) lock will be full of brackish water at low-level, but that is filled with fresh to come level with the penultimate lock. Surely the little bit of brackish water, being denser will sit at the bottom of the lower lock, well below the sill of the penultimate lock. The last lock (ocean-side) might experience the phenomenon you mention - as its water will have been largely diluted and comparatively fresh when the doors open to the brackish water.

[daletournier]

Originally Posted by LittleWing77

Well then, back to my original reply in Post #3.
If "uplocking" the water rushes in from the top of the lock, so - heaviest boats astern, recreational boats up front.

If "downlocking", the water is let out from the bottom of the lock like water rushing out of a bathtub. This time, you'd want the heaviest boat in front, closest to the water rushing out.

I guess you'd have to see it from a risk-assessment perspective: Hypothetically, if in the first case it was opposite - and you had the commercial vessel up front, you would open the lock, water would rush in from the top of the lock and if the big, heavy vessel began to move excessively and/or broke free, it could potentially smoosh all the little vessels behind it quite easily. If it's in the back of the lock as the water rushes in, it's not going to do anything except move perhaps side-to-side or bash into the end
the lock.

In your "downlocking" scenario, same thing. As the water is rushing out, you want the heaviest boat near the suction. That water rushing out will (relatively) assist in keeping that heavy commericial vessel in place at the back of the lock and away from the smaller lighter vessels.

Does that help?
Warmly,
LittleWing77

In the last lock Panana city side which has the most turbulence we had a very large car carrier right up our bum.

[LittleWing77]

Sorry, Dale, I had deleted my post almost immediately because I thought I would be contributing to the confusion - and obviously I'd got it wrong.

DefinitelyMe's Post #16 seems to have sorted it out.

Best,
LittleWing77

[daletournier]

Originally Posted by LittleWing77

Sorry, Dale, I had deleted my post almost immediately because I thought I would be contributing to the confusion - and obviously I'd got it wrong.

DefinitelyMe's Post #16 seems to have sorted it out.

Best,
LittleWing77

Hi mate, I hadn't read all the posts.

[DefinitelyMe]

Originally Posted by Lodesman

I like the rest of your explanation, but this part doesn't make sense. The locks are filled by freshwater. The final (lowest, ocean-side) lock will be full of brackish water at low-level, but that is filled with fresh to come level with the penultimate lock. Surely the little bit of brackish water, being denser will sit at the bottom of the lower lock, well below the sill of the penultimate lock. The last lock (ocean-side) might experience the phenomenon you mention - as its water will have been largely diluted and comparatively fresh when the doors open to the brackish water.

Yes you're right, it is brackish, but I'll have a stab at an explanation:

First, a couple of points to clarify:
- the penultimate and last locks are back-to-back
- The tidal range on the Panama City side is over 20 feet.
- minimum depth in the locks is about 40 feet.

So let's say it's high tide, and minimum depth in the last lock is therefore 60 feet. Lock doors open to the Pacific. Salt water is more dense, so it forces it's way into the lock underneath the layer of fresh, or brackish, and the fresh will rush out of the lock. Compound that effect with fact that whatever ship is in the lock is forcing itself out, and in return forcing salt water in to replace it. By the time it's done the water in that lock is basically all salt. Now the door closes and the lock begins to fill with fresh water. I can't find the numbers but, at least at high tide, it doesn't take much fresh water to top up the lock. Maybe 15 feet or so, making the water in that last lock about 4/5 salt.

When we did it it was high tide. The doors opened between the penultimate and the last locks the whole raft of small craft was catapulted forward, with the line handlers sprinting along the dock to keep up despite all of us having our engines quite hard astern. The surface of the water was full of dying fish due to the sudden change in salinity. It was quite surreal. The wheel was torn out of my hands and the rudder jammed hard over due to our astern speed through the water, but still we were careening towards the far lock door. Fortunately the advisors had positioned a big Leopard in the center of the raft and the helmsman of that boat was excellent, otherwise we'd have been in trouble. Many yachts have suggested that the authorities allow us to go into that penultimate lock backwards so as to maintain steerage, but they won't allow it for some unknown reason.....

Interestingly I haven't heard of such difficulties on the Caribbean side (anyone care to refute that?). Perhaps because on that side the last lock doesn't need to be so deep owing to the reduced tidal range?

[Lodesman]

Sounds plausible. That is predicated on a spring tide - neap range is about 6 ft, and having the lock ahead maxed out (Panamax vessel) prior to your entrance. IME the water level isn't quite even when they open the doors - and there is always a bit of water rushing out of the lock. I've noticed that in other canals too.

[jkleins]

Originally Posted by Jim Woodall

I should have been more clear:



During uplocking, regardless of the particular lock, recreational vessels are astern of large commercial vessels. During downlocking, regardless of the particular lock, recreational vessels are forward of large commercial vessels.



jkleins, was your experience different when uplocking and downlocking?



I asked this on the blog of some sailors who had transited the canal several times over the years in both directions.They didn't know the reason, but in 5 total transits over a decade it was the same procedure for them each time.



Again, there must be a reason but I can't find a definitive answer.

Yes I think I just misunderstood. We were behind uplocking and in front downlocking. Just going the opposite direction then you. I think the explanation about the water going in and out is the answer. We were behind a big empty ship that hit the gas hard to take off and nearly swamped us. Our advisor was yelling in the radio and he stopped in time. I would not have wanted to be behind him if he needed to do that for very long.

[jkleins]

Originally Posted by Lodesman

So while I understand your meaning as East = Gatun locks, that is actually further west than Pedro Miguel and Miraflores.

That is why I said “coast”. No confusion in that [emoji3]

[belizesailor]

Originally Posted by jkleins

We were the exact opposite. Behind on the west coast and in front on the East

Originally Posted by Lodesman

Which direction did you go? It's easy for there to be a misunderstanding when talking about the canal - as was mentioned earlier you travel east (actually southeast) going from the Atlantic to the Pacific, and vice versa. So while I understand your meaning as East = Gatun locks, that is actually further west than Pedro Miguel and Miraflores.

Just to clarify, Panama does not have either an east or a west coast. It has a north and a south coast. The canal runs roughly N-S.

[belizesailor]

Originally Posted by DefinitelyMe

To answer the OP's question. Our advisor explained this to us.

For both sets of locks, the ship we were with was maxed out on draught and beam, so when it's coming into or going out of a lock the hardest part is forcing the water around and underneath the ship and out of the lock. So as the ship comes in it pushes water ahead of it and when it goes out it's trying to suck water from forward and push it back to fill in the space behind it. Apparently, during these maneuvers the ship's engines will often be full ahead. Make sense?

Going in is always a little easier than going out, because going in the water rises (by a LOT!) and then spills over through the overflow ports into the next section. But going out there's nowhere for the water to come from except in front of the ship.

So, the first set of locks you're going up, which means that the ship comes in shallow but has an easy time leaving because it can suck water under the keel. It makes sense to have small boats behind because the ship has a pretty easy time and doesn't need to be going full ahead to get out of the lock, but might run into the small boats if they were ahead.

But in the second set of locks it's much harder because the depth under keel is virtually nil as the ships are coming out of the locks. They are full ahead and ours still took about 15 minutes just to get out of the lock. So you want the small boats ahead. They can scurry off as soon as the lock doors open and be tied up in the next one ready to go when the ship finally gets there.

There's one other thing - in the penultimate lock, the lock doors open and all the salt water in the last lock mixes with the fresh water in the penultimate one. Because salt water is more dense it goes under the layer of fresh, and the fresh water (along with anything floating on it) rushes forward. This is by far the most dangerous lock for small boats, which often end up spinning around all over the place or being slammed into the (closed) lock doors at the other end. They would rather have yachts hitting the lock doors than a ship, which is what would happen if the yachts were behind.

This is how our advisor basically explained it and it makes sense to me. Cool eh?

Cool. Thanks for posting the explanation!

A video of currents ripping in the locks as you describe above.

https://www.dropbox.com/s/kcresenhe9...92107.mp4?dl=0

[Lodesman]

Originally Posted by belizesailor

Cool. Thanks for posting the explanation!

A video of currents ripping in the locks as you describe above.

https://www.dropbox.com/s/kcresenhe9...92107.mp4?dl=0

Don't think this shows what was described - it's just the turbulence from the locks flooding. Not a great view.