Wake of the Stena Germanica — what’s going on there?

After having talked about wakes quite a bit recently, I’m going to show you a couple more pics today (bit not as many as I did two days ago, sorry! ;-))

And today we are focussing on the wake of one specific ship, the Stena Germanica that we sailed on for a mini cruise to Gothenburg (highly recommended!!). And even though that cruise sadly ended a month ago, I am still puzzled by what we saw:

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Look at the turbulent wake directly behind the ship. Do you see how the two sides are markedly different from each other?

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One side seems to be a lot more turbulent than the other.

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And I didn’t find an explanation for that. According to the internet, the ship has two propellers and on each of those propellers the pitch of the blades can be changed so that the propeller can always run at a constant speed and the ship’s velocity is changed by changing the propeller blades’ angles.

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Maybe that’s what is going on? But would they run two propellers at different pitches even when just steaming straight ahead?

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Btw, look at that beautiful wake pattern! You can see both the feathery V going out from the ship and those half circles filling in the V. I don’t think I have ever seen that this clearly on a ship this size before. But then maybe I just wasn’t observing well enough.

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I love it!

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Now. The next morning: It is quite windy now, and the difference between the two sides of the wake is quite pronounced. Also very interesting: The foam on both sides is behaving very differently! One side (the upwind side) has a much sharper edge than the other.

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But this surely can’t be the effect of just the wind?!

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Looks great though!

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Also very interesting: When arriving in Gothenburg, we met another Stena Ferry, and the same thing could be seen. Here she is after she passed by:

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And her wake stays visible for quite a while with this marked foam stripe right in the middle of the wake, as if she had counter-rotating propellers that set up a convergence zone there?

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Same phenomenon again when leaving Gothenburg later that day:

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And arriving in Kiel the next morning, we could beautifully observe the different parts of the wake again:

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What do you think is going on here? Why is the wake of the Stena Germanica not symmetric? I’m having sleepless nights over this :-)

More wakes

And now you thought I was done showing you wakes? Ha, I was not nearly done! I told you, watching waves makes me happy :-)

And from Stena Germanica’s sun deck we had an excellent view over the Kiel fjord and later the Port of Gothenburg…

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Expedition learning

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Last week, we ran an “expedition learning” course for 17-year olds. They were separated into several groups, working on different topics, and mine (unsurprisingly) worked on waves. You can see here what kind of stuff we observed when first testing the stretch of coastline we wanted to do our expedition to. And now you’ll get a picture dump of the actual expedition.

We started out in not-so-ideal-but-really-not-too-bad-either kind of weather, as you can read off the tracks below: It had been raining a little, but not very hard, and it had stopped by the time we got there.

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The drift lines looked quite promising.

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My group dove right into it (only figuratively, luckily, not literally). However I wasn’t quite sure if this guy knew what he was getting into?

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At this point we were still very close to the car, so I thought that it might be quite smart strategically to let them figure out here how high the waders go and what happens if the waves are higher than the waders… And the wakes of two ships  meeting up at a headland are a very good place to learn about that kind of things!

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This headland is a very good place to start observing waves in any case. Especially at the typical wind direction found here. Because then, looking back from the light house to the land, you see a large area that is sheltered where waves only build up gradually. Which is a very nice contrast to the waves arriving upwind and makes it very easy to observe differences.

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And then if you look downwind from the headland, you see waves sneaking around the headland from both sides. Those coming from the right are from the fully developed wave field that has been growing all the way down Kiel fjord, and then those coming in from the left are the ones that only started growing downwind of the little barrier shown in the picture above.

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Can you see it? Maybe easier on a panorama kind of picture?

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Of course we always like to look at the ring waves that appear when other waves hit stones…

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I didn’t foresee that wave watching would happen mostly from within the water, but the guys in my group made a good case for walking on the sand bank to actually measure the wave hight depending on the water depth (rather than just observing and estimating from dry land, as I would have done), but why not?

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Luckily, they found the shallowest part of the sand bank in exactly the same spot I would have told them to look for it based on the wave field ;-)

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Btw, a nice example of coastal dynamics right below. We had a coastal dynamics group, too, but I don’t even know if they looked at this kind of stuff, I mainly saw them taking soil samples.

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And I know I made the same observation in the same spot last time, too, but I think it’s fascinating how the different directions of the ripples and drift lines and waves all come together.

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In any case, a nice day at the beach!

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Well, most of the time anyway.

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Luckily, we found shelter!

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Those, btw, are Annika and Jeannine, who were working with a different group on coastal vegetation.

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But: New and interesting pattern on the beach once the rain was done!

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The kids spent the next two days putting all their observations on maps and preparing a presentation, and I am really happy with how it turned out. Of course there is some room for improvement still, but how boring would it be if there wasn’t? ;-) All in all I think it was a pretty successful course!

Wakes and what they do to the sun’s reflection

When I said that wake watching made me happy last week, did you really think those were all the wakes I was going to show you? Ha! No, I have plenty more! :-)

Today, I want to show you a couple that have one thing in common: the way that they show up against the sun’s reflection and thus become a lot more visible than they would be if they were just reflecting a uniformly blue or grey sky.

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Weekend wave-watching

Of course I did not only take pictures of lighthouses and instructional activities during the teacher training at Lotseninsel last week. I also took TONS of pictures of water! Some of which I’ll share with you now.

For example below you see where the Schlei flows into the Baltic Sea. This is actually a fairly narrow outlet, and you can see the strong current and the eddies that are formed where it flows into the Baltic Sea! It had been raining a lot previously, so there was a lot of water trying to get out of the Schlei!

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A similar pattern can be spotted at the outlet of the marina, but in this it’s mainly wind-driven.

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And very nice here: Long swell and short wind waves on top of it.

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Of course I also looked at wakes. This is a particularly nice one:

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Oh, and reflections. Isn’t it super pretty how the mast gets reflected with all these little twists and turns?

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And then we had some shielding from the wind, and waves only appearing after a certain fetch.

Btw, that’s the house we all — and all the teachers — stayed in.

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Here we see waves being dampened by some algae stuff, and being deflected downwind of those patches.

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Here is another view of the strong current going out of the Schlei and the distinct separation between the two water masses.

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And now the same thing in combination with the sailboat’s wake. So pretty!

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When we were on our way home, the wind had picked up substantially and we saw lots of foam stripes! Langmuir circulation, nowhere near the coast line.

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Here we get a last glimpse of the house we had stayed in… And more foam stripes!

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And some more ;-)

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And then in Maasholm, we see the waves arriving upwind of the pier and then the tiny ones in the sheltered area. You can see a gust of wind somewhere in the foreground to the right, where there are all those small ripples in a darker patch.

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It was a pretty windy day!

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And more foam stripes…

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And a wake!

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And another wake!

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And just a couple of pictures of water, because I love water.

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Reflected wake

The best ship-watching of the year happens during Kiel Week (even if I do a fair bit of ship-watching year round ;-))

But this year, I was absolutely fascinated with wake-watching. Look at the sailing ship below and its beautiful wake!

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You very clearly see the streak directly behind the boat, caused by turbulence where the hull pushed through the water. And then there is the actual wake, fanning out from the ship.

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And then that wake gets reflected on a sea wall as the ship is sailing past!

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Watching things like this makes me happy :-)

Wave watching 

This is an old picture from early spring, but I just love how the reflection of that pier shows up the different wave lengths so clearly. The longer swell wouldn’t have been visible just from reflections of the sky…

Refraction of waves towards the beach

As you see from my parents’ attire and the lack of leaves on the trees, these pictures are not brand new. But still interesting: Do you see how the waves are bent towards the coast as they run into shallower water?

And can you believe I still have to look up which one is refraction and which one is diffraction to make sure, despite having a PhD in oceanography? They really should consider retracting that. I am pretty sure I “was instructed” (avoiding to say “learned”, since I clearly didn’t) about this in a lab during first year physics. On the other hand, I know where to look it up. Does that count?

And maybe it’ll help if I write it down once more:

Diffraction is what happens to waves behind slits or obstacles.

Refraction is what happens when waves run into shallower/deeper water (or into a different medium if we are talking about light waves) due to dispersion.

Does anyone know a nice “Eselsbrücke”/mnemonic/way to remember?

Diffraction of waves around obstacle

I have always really liked the artwork you see below that was installed in Store Lungegårdsvann when I still lived in Bergen.

But on the pictures here you also see how awesomely waves are diffracted around it.

Pretty and interesting oceanography? What’s not to love? :-)

Traces in the sand

Yes, I am really that fascinated by sand that this is the second post in a week about it.

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And I still think the picture below looks like the place in Qumran where the Dead Sea Scrolls were found!

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