Rav Metzger was asked if yachts require a mezuza.

The question is based on the fact that people can stay on yachts for days and weeks at a time, and perhaps large boats are not equivalent to the boats referred to when the halacha states that boats do not require a mezuza.

Rav Metzger delved into the issue and decided that if the yacht is at least 2.5 meters by 2.5 meters (what yacht would be that small anyway?), and the intention of the boat is to be lived in for days at a time, rather than just hours at a time, the yacht would require a mezuza, though a bracha would not be made upon installment.

I should add my usual caveat, if you are a yacht owner and wondering if you need to put a mezuza on your yacht, ask a rabbi and do not rely on piskei halacha sourced on the internet.

(source: Srugim)