The tall guys onboard spend a lot of time ducking, but the main issue is that they can't stretch out in their bunks. I think anyone taller than about 6'2" has to adopt a feotal position. Never bothered me though...
Joined diesels in 68 , was and still am 6'4, bloody hard to get used to , but after a week or so just forgot about it. Took a while to get a bunk 'athwart' ships so i could stick my feet out of the bottom of the bunk though!got easier after that.
Visited an O boat last year and must admit i wondered how the bloody hell i managed, but then it was all an adventure then !
GO FOR IT! You wont regret it, trust me.