that's pretty quick...........but not enough!
however with a government that can't make it's mind up as to whether the hydrocarbon consumption efficientcy of the diesel is better or worse (for them!) than the emission specific products - and therefore simply tax the more efficient diesel vehicles will thinking about it; anything could happen.
personally the ideal should surely revolve around
(1) cleaner diesel (why not simply insist on lower sulpher diesel for all applications)
(2) more efficient marine diesle engines (already done via the appropriate EU regs coming into force)
market forces will then deal with the rest.........these will drive up the cat market for many of the reasons quoted but as many here have said running a smallish cat with a really efficient DIESEL engine is certainly a good bang for bucks solution in many many instances (as Victor has been outlining for a long time).
finally I am somewhat surprised that this firm hasn't applied for low tax petrol to be available to those purchasing their ecoboats!