A week ago already, Frauke and I went on an evening walk in Kiel Holtenau. Beautiful wave watching to be done there as always! Here you see the one side of a ship’s V-shaped wake approaching our vantage point. You can see the individual “feathers” of the wake: Short wave crests, all parallel to each other, but slightly shifted to the side to form a straight line (well, two straight lines to form a V with the ship at its tip, but the other side of the V is not visible on this picture).
And this is what it looks like when the wake has moved past us: Looking on the back of the feathery shapes. The ship that made all these waves has long sailed away.
Wakes are always interesting to watch. But usually, I am showing wakes of ships going straight ahead. So today, I have something cool for you: The wake of a ship doing a 90 degree turn!
And what that does is that the feathery wake that is usually V-shaped now gets deformed!
And this deformation of the wake means that on one side of the wake, the feathery waves that are usually parallel now become fanned open, while on the other side they get bunched together. See?
After the ship had gone a lot further, there were still effects of its wake visible, both of the waves created as well as the turbulent wake that is still visible in a surface roughness that is different from the rest of Kiel fjord, and a little foam.
Fascinating how long such a wake stays visible!
And fascinating that such a small boat — even though it was going a lot faster — does create waves that are a lot higher than the much larger ColorLine does!
If you look at the large ColorLine, you see that there is a large turbulent wake, but (at this speed) hardly any waves created, so hardly a V-shaped wake!
I’m lucky to have great friends like Alice, who was spontaneous enough to go on a mini cruise with me today (for which I was only given tickets when I was already on my way to meet her somewhere else). So we boarded the historic MS Stadt Kiel and the adventure began! (Note the Europe flag? Hope you’ve been voting already when you are reading this, otherwise stop reading and go vote! :-))
I had never been on the MS Stadt Kiel before, even though I’ve seen it many times. It’s lovely inside — historic charm and the smell of marine diesel. What more could you want on a gloomy grey Sunday? And a super nice crew of volunteers who run the ship!
Plus we got to see all my favourite spots, like the light house at Holtenau. You also see the pilot station right behind the light house, that’s where the pretty orange pilot ship lives that you see at least in every other of my blogposts ;-)
And the Kiel Canal locks at Kiel Holtenau; looking at them from Kiel fjord. I usually take my pictures either from the shore on the left close to where you see the tower, or from the bridge that you see in the background.
And then, as you do on historic cruises, there was Swing dancing with a dance crew who was performing for us and then even gave us the opportunity to join in, which, of course, Alice and I did. Unfortunately I wasn’t wearing exactly historical costumes, but hey! It was fun! Thanks, Christian! :-)
For privacy reasons as well as for fairness, I had to give everybody the same face that I am making on the picture ;-)
Yesterday, I took some pretty pictures of a red balloon floating on Kiel fjord, some seagulls swimming close to it, and — of course, most importantly — the seagull’s waves. You see some that they just made where you can still see how they relate to where they are swimming now. But then there are also these large circles from previous movement, and the origin of those we can only guess. As we see from the seagulls’ wakes, they haven’t been swimming in that direction long, and they started out from a resting position. Maybe the large circles are from when they landed? We can only speculate.
I’m showing you the pictures of the seagulls and the ballon because I think they are pretty, but also to have a reference for what “normal” waves look like. “Normal” meaning that they are waves whose restoring force is gravity.
There is, of course, other kinds of waves.
Check out the picture below. It’s super choppy, but do you see parts that look different? It’s an overall choppy day, so it might be a little difficult to see what I am talking about.
Let’s zoom in to see some capillary wave action! Capillary waves are the ones that are restored by surface tension rather than gravity. They are a lot shorter than “normal” waves, wavelengths are only up to less than 2 cm long! And they often appear as several wave crests right behind each other, like below. Short wavelengths travel faster than longer ones, which is why from a main crest, more and more capillary waves emerge which seem to be bunched up moving right in front of the main crest. Pretty cool, I think!
Edit, a couple of minutes after initial publishing this blog post:
I saw a friend use a comic app on Instagram and, of course, went down that rabbit hole. So here is a recap of the pictures as the app sees them below. Do you feel like the waves are easier to see in the comics than in the pictures?
Below, you see the seagulls as they have just started paddling forward, and the large circles are still fairly close to where the seagulls are.
Now the seagulls have swum a little further, but you still see where they initially started out. And you see that the time lag between the two pictures really isn’t that large — the large wave ring hasn’t propagated a lot compared to the balloon (which is also freely drifting, so maybe that’s not the smartest comparison).
But my capillary waves become a little clearer now, I feel: The bunches of parallel wave crests on the right half of the picture that are now drawn in black (while all the choppy stuff is just shared, but not contoured).
What do you think? Are these pictures helping to show what exactly I am talking about, or is it just as confusing as before, only in a different way?
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?
(Disclaimer: The physics the title refers to are somewhere in the second half of the blog post when I am done rambling)
In case you are wondering why I am blogging so much all of a sudden: Sometimes I just love to spend a couple of hours on my sofa, drink something warm, and play with my blog (as I told you I would last Saturday, when I wrote all the stuff that got published recently [technically it’s still said Saturday morning as I am writing this, I am just scheduling all these posts to be published over the next couple of days. I usually select and upload the pictures I want to use on my blog the day I take them, and I always know what I want to write about them, too. In case you were wondering about my blogging process…]). Anyway, moving on.
The pictures for this post were taken a couple of weeks ago, when it was still feasible for me to be at Kiel fjord in the mornings when the sun was this low. Early bird and all, but these days the sunset is too early to just accidentally observe.
What really irritates me is how the condensation trails in the sky look like scratches on the picture. Even though I took the pictures on my phone and then watched them on the phone’s screen (so there is no way they could have gotten scratched somehow) I kept thinking they were scratches. But the pictures are still pretty…
But what the low sun made really easy to observe because of the sharp contrasts between lit and shaded sides of the structure, is how you can actually use the deformation of the structure in the reflection to determine the slope of the water’s surface.
As you know, you can only see the reflection of whatever is exactly in the pathway of the ray from your eye, reflected at the sea surface, and going out at the same angle it came in. Even if you were looking in the same direction all the time, if the slope of the surface changed, what you could see in the very same spot would change, too. Hence if you look at reflections on water, they move and get deformed as waves go past the spot you are looking at…
Above, looking at the white hand rail’s reflection, it becomes very obvious that the wave field is actually quite complex. There are waves that pull the hand rail’s reflection out to the right side, and those that move it up and down in the picture. I find it absolutely fascinating how some parts of the hand rail are visible several times in the reflection, how there are even bits of handrail that seem completely detached from the rest (see the little white dot inside a white loop somewhere in the bottom right?) and how the whole thing still seems so organic and smooth.
Below, you even see how you can see how each wave crest relates to a “spike” in the reflection.
When looking at waves in pictures, it is usually pretty difficult to see which parts of the pictures correspond to which side of the wave, the one facing us or away from us (unless, of course, the waves are breaking, or you see stuff like total internal reflection going on). But the reflections make it a little easier, I think.
And just because staring at the reflections made me feel a little dizzy, here is something to give your eyes a little rest: The view towards the Baltic Sea out of Kiel fjord.
Hope you are all having a nice day full of #wavewatching! :-)
Walking along a beach, first, the waves looked like this: One wave breaking at a time.
That’s the situation you also see in the foreground of the picture below, while in the background, a little further down the beach, something else starts happening.
If we look closely at that situation (shown in the picture below), there are several waves breaking at the same time, one behind the other.
And it isn’t just coincidence, it keeps happening throughout hundreds of pictures I took that windy Sunday. Why is that?
I think (and this theory would be easy enough to test if the water was warmer or if I wasn’t such a sissy) that the slope of the beach is just different on either side of this little jetty or whatever it is. The shallower the slope, the earlier waves of the same wavelength can “feel” the sea floor, or the shorter waves have to be to “feel” the sea floor at the same distance from the water line.
So I think the slope on the left of the jetty is shallower than on the right, making the incoming wave field that is the same on either side (I’m assuming, but give me a good reason for why it shouldn’t be?) behave differently.
Funnily enough, the only reason I ended up on that beach was that I wanted to go watch a cruise ship go through the locks and into the Kiel canal with a friend. And, funnily enough, the ship decided to not go through the Kiel canal, as it did the week before. So we decided that we should go to the beach. Very good decision! :-)
But here is a “before” pic from when I was still thinking I would be writing a blog post about the ship going through the locks. Isn’t the seagull hilarious, posing like that?
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
When it’s all foggy and there are hardly any waves, sometimes help comes from the most unexpected places. Today: condensation trails that are reflected on the water!
Isn’t it interesting to see how depending on the angle of the trails waves show up a lot or hardly at all? The condensation trail on the right really looks like a snake that fell into an ants’ nest, whereas the one on the left is wriggling calmly and composedly.
(I think the assumption that the waves are more or less the same for all trails is fair to make. Don’t you agree?)
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)