Tag Archives: ships

Ships displace huge amounts of water, and it doesn’t come back immediately when they are gone!

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Last weekend, while wave watching at one of my favourite spots, I observed something curious.

Look at the movie below, this is what the turbulent wake of a ship usually looks like right behind the ship: As the ship moves forward through the water, it displaces water and right behind it, it creates a hole that has to be filled in again by water from behind the ship and from the sides. So right behind a ship, water is sucked towards the ship. So far, so good.

But now look, there is a ship coming out of the locks at Kiel Holtenau.

What that means is that it is pretty much coming out of a dead end, since, in order to keep the water level inside the Kiel canal stable, the lock closes it off from Kiel fjord at all times by either set of doors.

The wake of the ship looks pretty normal so far:

But any ship displaces a huge amount of water. The one above is 115m long, 19m wide and has a drought of 5.4m (according to my favourite app). That means that it displaces almost 12000m3 of water! And this water has to come from somewhere (otherwise the ship would leave a trench in the water where it went, much like your hand leaves a trench when you pull it through sand at the beach).

But since the ship is coming out of a dead end, there is only so much water that can fill in said trench from behind and the sides. So even after the ship has sailed, there is still water moving back into the narrow entrance of the locks!

See below: (Surface) water on either side of the wake is moving to the right, driven by the wind. But in the wake itself, water is moving left, still filling in what was sucked out of the entrance of the lock! And that for quite some time after the ship is gone. At the end of the movie below, the camera turns and you can see the (white-and-green) ship sailing away just to give you an idea of how long this is after it left the locks…

Isn’t that cool?

P.S.: Yes, I though about whether there might have been water pumped out of the end of the dead end to fill up the lock chamber again, but I don’t think that’s it. Do you?

When commuting is actually enjoyable. #wavewatching

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What I love about my job (in addition to the awesome job itself, obviously)? That my office is located in pretty much the coolest spot in Hamburg when it comes to touristy views of the city. So much great wave watching (and ship watching) to be done here!

For example below, see the small ferry on the right, and how well you see the bow waves in this kind of light?

And below, it has turned and is heading out into the main Elbe arm and you can spot the turbulent wake that reflects the sun very differently from the rest of the water on either side.

And then just casually strolling past dry docks, container terminals, huuuge ships…

I really enjoy this every day! Hamburg, the gateway to the world.

Sightseeing in Berlin? Any excuse for a #wavewatching trip!

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Berlin is full of interesting history to discover … for example that of ships that have gone past on the Spree! :-D

Let’s start with some easy wave watching. In the picture above, you see a ship and its wake (both parts: the turbulent one where the ship has gone, and the feathery wake that forms the V with the ship at its tip). And you can make out the wake of a ship that has already gone round that bend of the Spree: the turbulent part showing a different surface roughness, and reflected remains of the feathery V on the right shore of the Spree. So far, so good!

Below, you see two turbulent wakes: The one of the ship you still see, and then the one of a ship that went the other way, but already went out of the area captured in the picture.

Berlin Cathedral Church seen from across the Spree

And here is a series where you see the feathery wake reach the side of the Spree…

Bode museum and television tower Berlin

…get reflected there…

…and then meet the reflection of the other side of the V to form a checkerboard pattern! Would you have known what’s going on here if you hadn’t spotted the ship just about to leave the picture, or seen the previous images?

Below is another nice one. What happened here? A ship sat there, waiting, and then started moving again right before I took the picture! This is the beginning of a turbulent wake right here.

Reichstag, home of parlament

And below another nice wake plus reflection.

And here you see another feathery wake, plus the turbulent wake of the same ship on the other side of the Spree.

Reichstag, home of parlament

Similar picture as above, except in a different spot…

German Chanellery in Berlin seen across the Spree

Yes, that’s a pretty good representation of what sightseeing trips with me are like ;-)

Wave watching at the locks in Kiel Holtenau

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Yes, we are back to wake watching! Today I went to a new-to-me wave watching spot: The bridge across Kiel canal close to the Holtenau locks, which you see in the background of the picture below. And I should have checked out my favourite ship tracking app for better timing, I had to wait for quite some time before there were any ships apart from the small ferry which you see crossing right at the locks! But the wait was well worth it in the end!

In these pictures, you see very clearly the different parts of the wake. The turbulent wake right behind the ship where the ship has displaced a large volume of water and where the ship’s propeller has induced a lot of turbulence. The turbulent wake is bound by the foam created by the breaking bow waves. And outside of all of this, the V of the feathery wake opens up with the ship at its tip.

I am super excited about these pictures. Do you see the wake reflecting on the right (south) side of the Kiel canal?

And while it was pretty easy to interpret the pictures above, and the one below is still fair game because the turbulent wake of the third ship is still clearly visible, even though the ship is not, it is getting more and more complicated, isn’t it?

But now, with two of the three ships gone, it has suddenly gotten a lot more complicated. And it doesn’t help that the sides of the canal aren’t completely straight which leads to the mess in the lower right corner…

This is definitely a new favourite wave watching spot which you might see more of in the future! This stuff makes me so happy :-)

Long-distance wave watching during sunset

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Have you ever noticed how much you can observe when you look at water from a distance? For example in these pictures, you see the tracks of ships that are long out of sight! Do you see the circle that one obviously drove before leaving our field of view?

For the ships far out in the fjord, you can’t actually see the waves so much as the turbulence they created that left the surface smoother, thus better reflecting the light from the low sun (and appearing yellow-ish). And how cool how you see how newer tracks run over older ones! Only for the ferry in the bottom left you can actually see the waves themselves.

In the picture below we actually see the waves that both ferries made.

Zooming in: How cool does it look to have these waves almost all the way across the water? And do you see how they are bound by the ship’s V-shaped, feathery wake? I find it really fascinating that there are such large surface elevations, but only inside of the ship’s wake.

I just love wave watching, even when I am not even that close to the water :-)

Ships sailing through trees

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Ships sailing through trees? What?

The other day I went on a trip to Husum with my sister and her family. While walking along the sea, we saw the weirdest thing: Birch trees growing in the middle of the water! From their positions it was clear that they were some kind of marker for the waterway, but it looked very strange. But google suggests that this kind of marker is very common in wadden seas, where the water is too shallow for traditional buoys.

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“Pricke” – birch trees serving as markers for the water way

When coming from the sea, you’ll see the birch trees on the port side of the waterway, and on the starboard side there will be poles with branches which are tied together on the very top of the pole, branching out below. Apparently this is called “Pricke” in german. You live and learn! :-)

Ship lift Scharnebeck

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Today I’m going to share a long movie with you, but I’m planning to talk about ship lifts in more detail soon. But just how awesome is it that they can lift ships (SHIPS!) 40 meters up just like that? Each of the troughs carries 5,800 t water. You see the counterweights move when the troughs move, and it is totally fascinating.

I went there with my parents, but this is pretty much all they saw of me for a very long time :-) Weirdly enough I was the only person standing right at the railing. Well, maybe not so weird considering how wet I got. But you’ve gotta do what you’ve gotta do and I definitely enjoyed watching!

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Fascination.

The movie below is sped up by a factor 3.5 because there was so much footage that I wanted to show…

Currents caused by thrusters

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Or: fast inflow into nearly stagnant water body

Did you ever notice how when certain ferries dock, they stop, already parallel to the dock, a couple of meters away from the dock and then just move sideways towards the dock? Usually they don’t even move passenger ferries any more, just use thrusters to keep them steady while people get on and off.

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Currents caused by thrusters of a harbor ferry in the port of Hamburg

But why this weird sideward motion?

One reason is the Coanda effect – the effect that jets are attracted to nearby surfaces and follow those surfaces even when they curve away. You might know it from putting something close to a stream of water and watching how the stream gets pulled towards that object, or from a fast air stream that can lift ping pong balls. So if the ship was moving while using the thrusters, the jets from the thrusters might just attach themselves to the hull of the ship and hence not act perpendicularly to the ship as intended.

But I think there is a secret second reason: Because it just looks awesome :-)

How the shape of your bow can save you a lot of time and money

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My dear ship builder and naval architect friends, if this post seems horribly oversimplified to you, you are very welcome to write a guest post and go into this topic in as much detail as you feel is needed :-)

So now my dear non-ship builder and non-naval architect friends, here is a post about ships. And be warned: it is very simplified. I have been taking pictures with a post on this topic in my mind for more than a year now, so here we go:

Have you ever noticed the bow waves that ships make?

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Bow wave on a ship somewhere in Cornwall

It’s pretty easy to imagine that a lot of energy is lost generating the wave field around the ship. Energy that could be used on propulsion or on something completely else instead.

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Energy wasted on creating an enormous wave field.

So what if the solution to this problem was really simple? As simple as a ball right in front of a ship’s bow, just below the water line? That would produce a wave field as seen below.

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Wave field created by a submerged buoy in a current.

And indeed that is what you see when you look at big container ships like the one on the picture below.

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Bulbous bow on a container ship in the port of Hamburg

So why would this work? In the picture below, I’ve sketched an over-simplified explanation. In A) you see a ship moving from left to right, and the bow wave that is created by the ship moving through the water. Then in B) you see the wave field created by a submerged ball (compare to the ball in the third figure in this post – that’s not so unrealistic!). And then in C), you see the water levels from A and B added together: They cancel each other out (pretty much). Voila!

Bugwulst

Sketch explaining how a bulbous bow cancels out the wave field created by a conventionally shaped bow.

Of course, it is not quite that easy in reality. Having a bulbous bow is only an advantage if you are planning on driving with a set speed most of the time, since the wave field created by both the bow and the bulb depend on the ship’s speed, and both have to be tuned for a specific speed. And you will still lose energy to the wave field that you are creating as you are moving your ship through the water, but not as much as before. But still, since you see bulbous bows on most large ships these days, it seems to be working quite well, and, according to Wikipedia, yields fuel savings of the order of 10-15% for any given speed. Not too bad!

“Isostasy” of ships

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Empty ships look weird.

Since we talked about the ship-and-anchor thing last week (you know – what happens to the water level when an anchor that was previously stored on board is thrown into the sea) I remembered that I took pictures when I went to Gothenburg in September that I had been meaning to share on here.

We (or I, at least) hardly ever see empty ships. For one, it doesn’t make a whole lot of sense economically to have ships driving around empty, but also the stability of ships is maximal at a certain position of the ship in the water. Therefore people will always try to drive a ship that is neither loaded too full or not enough. But don’t empty ships just look funny?

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Ships in the port of Gothenburg

Especially when you see sister ships next to each other where one is full and the other is empty (below).

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Ships in the port of Gothenburg