Shanties don't have nationalities - they come from the gaps between countries. But I never heard of Royal Navy shanties - all the info I've come across stated that, in the days of the canvas engine, singing on duty was a flogging offence in the RN (like most other things). They sometimes used a fiddle or other instrument to co-ordinate the work, but the singing of shanties was the preserve of the Red Duster. The best source of words/ tunes for shanties is still Hugill's works, unless you like to pick them up from recordings. Try the Chanty Cabin on the net.