The rooms of a ship are exempt from a Mezuzah. [However those ships that contain permanent rooms of living, as is common in all boats and ships of today, some Poskim rule they are obligated to have a Mezuzah. Other Poskim however rule that the rooms of all ships are exempt from a Mezuzah, even if there is a Jewish cabin member who is living on the ship. Practically, one is to place a Mezuzah without a blessing.]
Is a house boat obligated to have a Mezuzah by its doors?
One is to place a Mezuzah without a blessing. This applies whether or not it is one’s permanent residence.
 Michaber 286/11
 The reason: As it is not a permanent dwelling. [Shach 286/21; Taz 286/10]
 Aruch Hashulchan 286/27
 See Beir Moshe 2/88
 The reason: As boats are innately created for temporary dwelling, and hence cannot become obligated in Mezuzah even if one decides to make it into a permanent dwelling. [ibid]
 Pischeiy Shearim 286/11
 The reason: As some Poskim rule that all moving quarters are exempt from Mezuzah. [ibid]