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 ;-)
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)
You know how they say that the journey is the destination? That was certainly the case for my spontaneous mini-vacation yesterday (and how awesome is it that my #BestTravelBuddy is up for a cross country trip on a day’s notice?). We went all the way from the east coast to the west coast — which in Germany admittedly isn’t that terribly far — to visit the island Sylt in the North Sea for a day.
But it got even better when we reached the west coast. This is my kind of train ride!
Below is a view of the dam that connects the island Sylt with the main land, and here again you see how windy it is, and this is in the lee of the island. In the lee of those shallow dams you see that it really doesn’t take long for the surface roughness to increase again.
So are you excited to see the wind-ward side of the island now? I’ll post some wave watching from that side soon, but I first have to wade through literally thousands of pictures to cut it down to a handful. I’m already down to about the 100 best, but now I can’t decide which ones to post, because I like them all…
But here is a picture of the train ride back. Do you notice how there are regions with really low surface roughness on either side of the dam, suggesting that this dam is sheltering the water surface from the wind in two directions? Of course it isn’t — it’s just ebb tide and the smooth surface areas towards the right of the dam are wet sand that look similar to a smooth water surface.
So that’s my wave watching from the train! Excited to go back soon! :-)
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 :-)
After talking a lot about turbulent wakes this week, here are two pictures of different kinds of wakes. They are of course turbulent, too, but on a very different scale.
In the picture above, see how you see pairs of eddies on either side of the row boat’s wake? That’s where the oars were in the water! But this wake stays visible only for seconds, maybe a minute. Nothing you would be able to see for a long time from afar!
Same for the waves the birds made. Can you still spot that they were swimming in the same direction as the row boat and then made a 180° turn? Maybe you can, maybe you can’t, but that’s how quickly those wakes vanish.
Now below: This is a very interesting wake. Since the SUP board is pretty much flat on the water and doesn’t displace a lot of water while moving through the water, it pretty much only creates the V-shaped wake, not a turbulent one the way a ship does when it’s displacing a large volume of water in order to get forward.
Think I’ve said everything there is to say about waves? Well, then just enjoy this one from the ColorLine ferry that sailed past a couple of minutes ago… How beautiful is this? :-)
Since we seem to be on the topic of wake watching these days, here are some pictures I took when visiting my friend Liz at the European Cruise Service’s offices in Bergen the other day. She had already told me about the awesome wave watching to be done from their meeting room, but see for yourself!
Above, you see a very nice example of the turbulent wake of that cruise ship substantially modifying the wave field even after the ship is gone (or, in this case, after the ship has turned to leave in the other direction. Doesn’t this whole picture look very Titanic? Or is that just me?). What is going on there is that the turbulence introduced in the water by the ship and its propellers moving a lot of water around sticks around for quite some time. While the water is still moving due to the turbulence, “normal” surface waves can’t propagate in the turbulent area. The water’s surface thus looks very smooth there, a lot less rough than in areas where there are wind waves. And the smooth areas reflect light similarly to a mirror, whereas the rough areas’ light reflections seem to resemble maybe a disco ball?
Below, you see both parts of a wake quite well: The turbulent wake right behind that ferry (which will show up all smooth from a distance), and then the feathery V wake (with the ferry at its tip) that spreads on either side of the turbulent wake.
And you see some more old turbulent wakes in the picture above, for example one that the ferry in the foreground is following closely (see how it stretches out before the ferry?) and one that turns left to go towards the invisible Askøy bridge (you can still make out the ferry where the wake begins).
Do you see the potential of this wave watching spot? I definitely have to come back!
Even if you are not into wave watching, it’s a super interesting place to visit because it gives quite an interesting look on the city, even with Ulriken being disguised by the low clouds that day…
Would you be interested in a wave watching tour when you visit Bergen (or Kiel, or any other place)? If so give me a shout, we might be able to arrange something ;-)
Speaking of wake watching, the other day I wrote about long distance wave watching in the sunset, i.e. what kind of things one can deduce on surface roughness (and its causes) from different reflections of the setting sun on the water. And then I was asked why ships’ wakes were still visible for such a long time after the ships had already sailed. So here is my attempt at an explanation:
Check out the pictures above and below. In both you see the turbulent wake of the RV Kristine Bonnevie on our recent student cruise. You clearly see where the ship’s hull has passed through the water, moved forward by the ship’s propeller, which is very clearly introducing a lot of turbulence. And you very clearly see where the ship has not been: a more or less undisturbed wave field full of small wind waves, that looks substantially different from the turbulent wake.
Now why does the turbulent wake look so clearly different from the rest of the water for such a long time, even when the ship is gone? Shouldn’t the wake be invaded by surface waves at their wave speed?
Yes, that should happen, if the wake wasn’t turbulent. As the wake is turbulent, however, there are eddies moving the water around for quite some time after the ship has passed. If the water is being moved faster than the phase speed of the waves, they can’t propagate in there, the “flow” is too fast, the waves are washed away. See where the hydraulic jump is happening in the picture below, and waves seem to be squeezed together outside of the turbulent wake?
Just because it’s fun, here my hydraulic jump animation: the wave (person) is traveling exactly as fast as the current (escalator), it therefore doesn’t move. More Froude number animations + explanations here if you wanna look at what happens if the wave is moving faster or slower than the current…
Anyway. Back to pretty pictures. Below, you see a wake that is a little older: The surface is still a lot smoother than over the rest of the fjord, because the waves still haven’t propagated into the turbulent region. And when they do, longer waves propagate in first, because their phase velocity is faster than that of short waves. But the long waves’ effect on surface roughness is smaller than that of short waves, so the wake still appears smooth for even longer.
Only when all the turbulence has died down and the water is stagnant again (Or moving with the surrounding water) will the wave field be able to grow back to look the same as everywhere else. And therefore, even if you look at water from a distance, you can see where ships have been, even when they’ve long gone themselves.
It all began when I spotted a wake (the feathery, dark line going across the water behind that boat house) and decided I needed to show the world how cool it is to do #wakewatching.
Check it out in the images below:
The water is pretty calm, apart from some locally generated wind waves. But there is a long, feathered wave crest coming in. What I mean by feathered is that it’s not actually one continuous wave crest, but several crests that propagate shifted from each other, but in total forming what seems to be one long line. In the left of the picture below you can actually see the two wave crests that follow each other closely.
A little while later you can see the wake starting to interact with the shallow bottom — wave height increasing, and the sea wall — waves reflecting.
Below you see that the wave actually starts breaking when the water depth becomes too shallow.
And below you see the wave crests that were reflected on the sea wall!
The reflection is actually easier to see when we look down the other way: See the Vs with their tip at the sea wall, exactly where the original wave crests is transformed into the reflected wave crest?
Next time you see a wake approaching a sea wall, you should look out for these pattern — a couple of minutes well spent! :-)