Well, as long as the world won't ban yachts and cruiseships entirely, isn't it better to go as green as possible within the given boundaries?

I think the controversy is pretty similar to the debate around electric cars. Sure, from an environmental standpoint the solution should be less and less individual transportation in favor of trains, buses etc.

But before we do not act at all I personally prefer if we at least slightly reduce the footprint of cars, yachts, planes etc. with new technology.

Furthermore, if environmental considerations start to become fashionable among the rich ('my yacht is greener than yours!') it might trigger a real change process.

Is it greenwashing? Sure. Would it be better if yacht manufacturers do not give any shit at all? Absolutely not. I at least prefer them to do the lesser of two evils.