Hi This has come from a good source
The reason the MOD bought into this inboard boat was to replace the 5.4 models with petrol motors in them as they are banning petrol on board ships soon.
The trouble with them as I am told is when you load them up with say 8 people they are almost underwater !
The little 5.4 was not really designed for inboard motor + potentially 8 matlows....
I think someone in Avon hit the wrong keys on the displacement calculations computer box....