On Wed, 16 Aug 2017 04:43:06 -0700 (PDT), Christopher Tidy
wrote:

Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David Billington:

I don't think the guy I know that used to work for David Brown would
agree. While he is no longer full time he does get call upon to work on
North Sea oil rig gearboxes from time to time and has worked on large
ship gearbox installations in the past from what he has said.

It might just be that big gearboxes cost dramatically more than smaller ones, and so other solutions become economic. Could be that simple. I'm just interested to know if there are technical reasons about gearbox scaling which affect the choice as well.

Chris
It might be just that. Since the volume of metal increases by the
square of the diameter of the gear they must reach a point where
moving that volume of metal takes too much energy compared to the
amount of energy transmitted. So the cost of the gearbox plus the cost
of transmitting the energy just gets too expensive.
Eric