OK, success. Got there in the end
Four of the fishing boats at Herring Bay are static, leaving three moving. This is what I'm seeing using different wake files:
fx_wake_ss - Can't see any wake at all.
fx_wake_s - Only see the wake part of the time, sometimes on one but not the other two.
fx_wake_ijt1 - Good wake on all three but maybe excessive for this size of boat.
fx_wake_coastguard - Good wake on all three now but probably excessive for this size of boat.
fx_wake_m - Reasonable wake on all three.
I think fx_wake_m seems to be the most suitable but that's just my opinion. Anyway, thanks for your help, Dex.