Thanks Richie, but even from your vast photo archive you can't produce a close up of the ventilators probably because no one thought to photograph them. The current vents on sale are Ridged dome, Scalloped dome, Torpedo and Shell and a quick Google search for Flettner ventilators on railways coaches suggest a different shape to those mentioned above. As a modeller the first thing you see of a coach is the roof so it's nice to get it right. Apologies JB for taking your thread in a different direction.