The English sentence is ambiguous. Are you asking “Is is necessary to have a ticket…?” or “Would you like/do you need a ticket…”
Farantóireacht is a rather abstract word meaning “the act of ferrying”. Farantóireachta is the genitive case (“of ferrying”) and a ferry-boat is called bád farantóireachta (“boat of ferrying”).
If the context is clear it might be more natural to just say “boat” bád, rather than bád farantóireachta.
Gá is a noun meaning “need” and is usually used in a formula like tá gá le X ag Y (“Y has need of X” lit. is need with X at Y) or tá Y i ngá X+genitive (“Y is in need of X” lit. is Y in need of x). It can also be used in a pattern like is gá do… (lit. is need to/for) but although tá and is are both translated with the English verb “to be” they are very different (like ser and estar in Spanish). Is gá do… implies something is required or obligatory; tá gá le…ag… suggests something is needed (at the moment).
Another simple way to convey needing something is to say (literally) “X is from Y” — tá X ó Y or “X is wanting from Y” — tá X ag teastáil ó Y.
So, some concrete suggestions…
Singular:Dia duit! Ar mhaith leat ticéad don bhád (farantóireachta)? Plural:Dia daoibh! Ar mhaith libh ticéid don bhád (farantóireachta)?
“Hello! Would you like a ticket for the (ferry-)boat?”
Singular:Dia duit! An bhfuil ticéad don bhád (farantóireachta) (ag teastáil) uait? Plural:Dia daoibh! An bhfuil ticéid don bhád (farantóireachta) (ag teastáil) uaibh?
“Hello! Do you need a ticket for the (ferry-)boat?” (i.e. because I can sell/give you one, tell you where to get one, etc.)
Dia duit! An bhfuil sé riachtanach ticéad a bheith agat don bhád farantóireachta?
“Hello! Is it necessary to have a ticket for the ferry-boat?”