Hi, Throbert!

всё на х*й and всё на фиг don't have exact meaning and can be used mostly as exclamations in case of anger, irritation.
besides, всё на х*й is very rude as it contains the rudest Russian word

всё зря - is neutral and can be substituted by всё к черту, всё пошло к чёрту (lit., all went to devil), meaning 'it was in vain'

моряк is a job, profession (general word for any sailor)
матрос is technically a military rank if it's a military vessel,

but if on a civil vessel this means a specialist responsible for some non-navigation duties on the vessel (cleaning, painting, general works, taking care of the ship).

There is also a military rank (on military vessels) - старший матрос (senior sailor, literally).

You can use both words for "the Navy". Моряки would probably be used by most as it's means collectively just all sailors in the Navy on all types of ships regardless of their ranks and duties.