How does the 144 hour Visa impact on cruise ship passengers please?

We are a group of 4 adults going on a cruise in May 2019. We fly from Manchester United Kingdom to Singapore via Qatar. We pick up the cruise ship in Singapore and then dock in Vietnam, Hong Kong and then the cruise ends in Shanghai where we stay for 2 nights. We then fly back to Manchester via Qatar. We have been told that we qualify for the 144 hour twov, is this correct? Many thanks. S & M