British slang -

Spliced - splicing is a method of joining two ropes into one, hence also used as a term for getting married (officially or otherwise).

To "get your whack" generally means to get all that's due to you - your wages, perhaps (though not in the song quoted).

Hilo is the name of a port (Haiwaian, I think, but there's also a port called Ilo in South America) - songs refer to "going to Hilo" in that sense - it may have been used with some other meaning, or a shantyman may have just liked the sound of the word, or deliberately confused it with 'Hello' for effect. Hard to tell, with songs - sometimes expressions are just there for the song, and don't reflect usage in everyday speech at all.

Can't be any more help, I'm afraid.

Andrew.

PS - I did know about (Bar)Badian too.