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 :-)