Finnish 'Dark' class
 

Two ‘Dark’ class FPB’s were ordered for the Finnish Navy from Messrs Saunders Roe during 1955.
Named ‘Vasama 1 and Vasama 2 (Arrow 1 and Arrow 2), this is ‘Vasama 2’ rigged as an MGB with Bofors Mk 7’s mounted Fore and Aft on sea trials off Beaumaris, Anglesea.

Were they also Napier powered Ted? Did they have any influence on the design of the Nasty class of later years?

Yes 'Dartskipper' they were Deltic powered.
As you may know the Napier Deltic marine engine had a bumpy beginning in the RN. A simple explanation - for a very complex issue - coolant entering cylinders when shut down for any length of time.
By the time the Norwegian 'Nasty' class entered the scene (1960's), the issue had largely been identified and remedied, with the 20 or so vessels of the USN serving with some distinction I believe in Vietnam??

Thanks for the extra details Ted. I thought we missed a trick by not building any "Nasty's" for our own use. There's some footage of them on You Tube and of one preserved racing around the Baltic.

Regards.