Indeed, the number of ships equipped with Flettner rotors seems to be seriously increasing.
And this is understandable: considerable is the space saving by using cylinders with a lift coefficient Cl of 8.5 for a tangential velocity of 47 m/s and a wind speed of 10 m/s, all this for a reasonable power consumption. With higher winds the efficiency remains considerable even taking into account of lower Cl. And with lower winds we will be at the maximum Cl possible with a lower energy rotation expense. These rotors are solidly mounted, which can limit the power consumption.
We could find the space saving qualities within AWE field by the ease of stacking trajectories of units flying slowly and not having to half turn.
I think that vertical trajectories such like investigated in both chapter 12 (of which Garrett Smith (@WindFisher) is a co-author) and chapter 13 allow to benefit from a higher Cl with a current wind speed of 10 m/s (thanks to a relatively slower motion: “the cycle of Fig. 1.18 with a maximum of va = 14.26 m/s in the production phase” (Chapter 12, 1.5.1; and table 1.2: wind speed 10 m/s)), knowing that inflatable balloons seem to undergo a higher power consumption and that Modeling and control of a Magnus effect-based airborne wind energy system in crosswind maneuvers would lead to a too high power consumption, because of a too high linear motion leading to a too high tangential speed which is cubed.
Such a vertical trajectory would be possible with exactly the same material used by Wind Fisher which is a progress in reeling Magnus balloon field.