Well sorry, they probably didn't...

Boats are small, ships are big - boats go to and from Rottnest Island, up the Swan river or other estuaries - Ships travel on the ocean or sea & Boats go on Ships.

Anyone who migrated by sea to Australia over the past 200 years (excluding recent refugees) is pretty much guaranteed to have come on a Ship.

Nothing annoys an ex seafarer more than to have his/her life at sea referred to as he/she having spent time on a boat...

The First Fleet was made up of Sailing Ships, the diaspora's from England and Ireland in the mid 1800's and Europe after World War Two in the 1950's arrived by ship, anyone whose ancestors came to Australia by boat were probably refugees that came from Vietnam in the 1980's or the Middle East in the early 2000's, the rest of them came on a ship.

These are boats: They probably didn't come on one of these...

                Row Boats                                                  Sailing Boats                                                  Fishing Boats (maybe)

These are Ships: They probably arrived on something like this...

                Sailing Ships                                                Passenger Ships                                            Bride Ships 

Future Ships that they might arrive on...

                Space Ships                                                                              Star Ships                                                  Guitar Boat?

SO, no more talk about arriving by Boat eh!

Unless they did of course...