Tag Archives: wake

Hijacking other people’s “good morning!” tweets to talk about a duck’s wake

A beautiful picture: the pink sky, purple clouds, a peaceful channel flowing in between lush greens that the calm water surface mirrors back, a bridge somewhere in the background, connecting the shores, both in reality and in the image on the water. Early morning harmony. Hygge?

And what jumps at me?

Waves!

Which I think are really beautiful: Featured in the dark images of the trees on the water, a duck’s wake reflects the light sky back to us, thus becoming visible. And once we spot the V in the waves, with the almost invisible duck at its tip, we can see how the space between the feathery sides of the V is filled with half circles, connecting the feathers. They get more and more difficult to see the further away from the duck we look. The contrast becomes less clear where they aren’t set against the dark backdrop, and the more the waves dissipate with time.

This kind of waves is so common all around us, all the time. Did you ever really stop and look? It’s so worthwhile to really observe these things, to me that is happiness :-)

The Teltow channel and the bridge connecting Lankwitz and Steglitz, by Henning Krause. Picture used with permission

Spotting both the V-shaped and turbulent wake of a faraway ship on a calm day

The title says it all, I guess ;-)

In the picture above, you can still see the ship on the left, and having seen the ship, I am sure you can recognise the turbulent wake in the picture below, too: It’s the lighter blue stripe towards the horizon with darker, rougher sea surface to either side.

And in the top picture, you see individual “feathers”, i.e. parts of the V-shaped wake with the ship at its tip, coming towards us, whereas in the bottom picture, a little later, the one part of the V has reached us and we see the “feathers” as the wave crests that are more or less perpendicular to the bottom of the picture.

I find it interesting how the perspective makes it seem as if the wavelength gets a lot longer towards us, but that’s really only the perspective. Also the closest two or so crests are really hard to see — can you spot them? The closest one you can see better on the right side of the picture where there is a sudden change from a darker to a lighter part coming across, and the second one you see more easily on the left side, again, with a quick change between darker and lighter. And the third one is fairly easily visible all across the picture.

Do you do wave watching when you are at the water?

A #friendlywaves from a field trip in a Norwegian fjord

The other day, my friend and co-author Pierré sent me pictures he took during fieldwork in a Norwegian fjord. As I, sadly, wasn’t there, all I can do now is admire the pictures and wish I had been there. And, of course, do a #friendlywaves — an interpretation of a wave field that a friend sent me a picture of. Let’s see what he thinks about my interpretation!

So here we go. As you see, it’s a foggy day, and from the time he messaged me at, I know it was a foggy morning. The light seems to kinda be coming from a low angle which would support the morning (or evening) theory, but that’s always very hard to tell in the fog.

There are some waves on the sea surface, and below you see two distinct wave fields at a small angle to each other. What caused them?

I am guessing that the ones that look like sections of a circle are from some kind of point source, which would be located somewhere below and to the right of the picture’s lower right edge. Maybe something regularly dripping into the water, or a buoy being deployed. I think I’ve seen something like that when a CTD was coming up again and the wire was dripping as it went over a pulley. In any case, I am pretty sure the ship was on station as the picture was taken.

The second wave field, more or less parallel to the lower edge of the picture below, I would guess is the background field. Could be caused by anything, but nothing very close by: It’s not locally generated wind waves. If I had to guess it’s wind waves that have run for a little while. It might also be the ship gently rocking, radiating straight-ish wave fronts, but I doubt it.

As to what we can say about the spot the picture was taken in: There are no structures/shore lines really close by (otherwise we’d see reflections in the wave field), and the water depth is more than a meter or so — it’s definitely long compared to the wave length of the waves shown here as they can’t “feel” the ground (which we see from their shape — not shallow water waves).

Picture by Pierré de Wet, used with permission

The next picture, I am assuming, was sent to me to capture the mood. And to make me jealous. Yes, it worked ;-)

Picture by Pierré de Wet, used with permission

Below, we see that the ship is now moving. We are looking down and back and see the wake developing: The turbulent wake in the top left of the picture, one side of the feathery V-shaped wake on the right of the turbulent wake. The feathery waves are fairly steep, but that’s because of how they were generated, not because of any interference with the ground. The ground is still more than at least two or so wavelengths away (and it better had be, judging from the size of the ship).

There was hardly any wind when this picture was taken, the sea surface doesn’t show any locally created wind ripples.

Picture by Pierré de Wet, used with permission

I think it’s so fascinating to see the sharp line in the lower middle of the picture, separating the part of the sea surface that has been influenced by the ship from the one that hasn’t received any signal of the ship’s presence yet. If you think about the V-shaped wake as of the ship’s Mach cone, the outside of the V is where people would first hear the sonic boom after the ship has flown past!

The picture below is looking at a similar situation wake-wise. Now, though, there is a little wind: You can clearly see the enhanced surface roughness, and indeed individual capillary waves, in the bottom right corner.

Below is a third picture of the same situation. Now there are some small waves in the surface, however not locally produced, I think. Maybe they already sailed out of the spot (can you say breezy? It’s really not a windy spot) shown above?

Picture by Pierré de Wet, used with permission

What I find fascinating above is how clearly you see the one leg of the V-shaped feathery wake develop, and even in the foreground of the picture how you can see individual turbulence cells from where the bow wave broke as the ship sailed through the water.

What else do you observe? It’s not so easy to look at other people’s wave pictures and make sense of them! How did I do, Pierre?

Windy days at Holtenau locks: Now THAT’s a turbulent wake!

Now that the weather is nice and sunny again, here is what it looked like only last Saturday. It wasn’t even really stormy, but windy enough so that the ships leaving the locks at Kiel Holtenau were working a lot harder than usual. Especially difficult when you are almost empty and then there is a lot of wind! See that wake?

Right behind the ship you see above, there was a second ship leaving the locks. See how milky the water looks where the first ship went from all the air bubbles that were pushed under water by the ship’s propeller? You can even see some of that water spreading underneath that floating barrier in the foreground!

And see the difference between the waves on the upwind side of the ship and the downwind side?

Here is the picture that my friend sent me that she took from inside of the café that we were sitting in before I HAD to go outside and take pictures. If I am being sent pictures of my back every week by my friends, are they trying to tell me something? :-D

Wave watching at Kiel Holtenau locks

On Sunday, I set out to see a large cruise liner go through the locks at Kiel Holtenau.

What happened, though, was that a ship with a smiley painted on its deck came first. Do you see the two shadows to the right of the ship, the left one aligning with the one side of the wake’s V? That’s the pillars the bridge is resting on.

This ship has a very interesting wake, since it consists of several Vs. Not quite sure why. Also, it seems to be driving in a very non-straight line, judging by its turbulent wake.

But watch what happens when the wake hits the sides of the canal.

The green thingy interrupts the straight line of the shore and creates these beautiful ring waves!

A little while later they have spread half way across the channel, while on the other side, the wake is just reflected on the shore.

It looks funny how the reflections are so asymmetrical relative to the ship, but of course the ship isn’t driving in the middle of the channel, so they have to be.

And on the other side of Kiel fjord? Yep, the cruise liner speeding past the locks. Clearly they decided to not take the shortcut through Kiel canal.

And now the small ferry is starting to cross. And in the background: The cruise liner!

I realize the earlier pictures in this posts were a lot nicer than these, but look how funny: Above you see the small ferry going around the larger ship, and the wake tracking where it went on its turn. And below, it has turned into a V! Waves are funny.

Interesting pilot ship #wavewatching at Kiel canal

Some throwback Friday evening wave watching (at the locks at Kiel Holtenau with my friend Sara for a nice and relaxing end of the week) to start the new week. The best!

First: The pilot boat going towards the locks. Unusually visible wake — they are going fast today! Plus an interesting sheltering of waves: The wind is coming towards us so outside of those floating pontoons are a lot larger than the ones on this side that haven’t had enough fetch to build up.

Below we see the same wake: But do you see how it’s just ending on the left? That’s because the pilot boat went in behind the jetty on the far side of the fjord, and it’s only these bits of the wake that were able to propagate outside before the boat went in and the waves don’t make it out of the small channel created by the jetty.

And below the pilot boat going out again in a curve: Love how you see the turbulent wake as well as the deformed V-shaped feathery wake. When you look from the pilot boat down on the picture, do you see the individual “feathers” of the V? Love this perspective on wakes!

And this is what you will see of me when you meet me for a coffee anywhere near water. Sorry Sara, but thanks for the picture! :-)

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

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 ;-)

You are watching seals? I am watching waves!

On a recent evening stroll with a friend, the seal basin looked like this:

“Do you think there are any seals in there today?” she asked. “Why yes, of course, don’t you see the waves?” I replied. Because obviously in a basin sheltered by the wind and with no moving parts in it except possibly a seal or three, there is no other mechanism that I could imagine that would create such a wave field. Sometimes I wonder what everybody else is thinking about all the time that I am thinking about waves while they aren’t… Who’s missing out on the cooler thoughts, me or them?

Anyway, we got to do some proper seal watching and wave watching, respectively:

Pretty, isn’t it? the wake of a seal. Pay close attention, I might be testing you on this some time soon ;-)

Wake comparisons: Row boat and motor boat

I just love this picture: The two boats in the front are going at the same speed (the trainer is driving right next to the person in the row boat over a long distance), yet look at how different the two ships’ wakes look!

The motor boat has this huge, breaking, turbulent wake. Even though it rides so high up in the water, it displaces a lot of water and creates a wake with a large amplitude (how large the amplitude is is visible in the picture below, where some poor people were sitting in row boats when a motor boat sped past. But also here: Look at how cool these feathery waves that constitute the wake look together!).

But then, going back to the original picture (which I am showing again below) — look in contrast at the row boat’s wake. You see the paired eddies where the oars were in the water, and you see a tiny little trail where the body of the ship went. But that’s all. Yet both boats are going at exactly the same speed! Pretty cool, isn’t it? (Also pretty scary how much energy the motor boat is spending on moving water and moving a larger hull and a heavy engine rather than just propulsion when the payload of both boats is more or less the same — one person)