72 or 144 hour?

As long as you don't fly into Beijing from Japan, you're fine for the 144h twov (72h twov doesn't exist anymore in Beijing).
But beware if your first stop after Tianjin is another chinese city, you will need a visa for your stay in Beijing.
But if you go straight to Japan, you don't need a visa.

Thanks for the reply Thomas, the ships sales straight to Japan although about a week after that we are docked overnight in Hong Kong then onto Vietnam & Singapore.

This is perfectly fine because Hong Kong has separate immigration and you don't need any kind of visa for your travel or a stay in Hong Kong.

To conclude, you are definitely eligible for 144 hour visa free transit and you don't need any kind of visa. Just bring the printout of your cruise ticket and a confirmation of your accommodation booking in Beijing.

Thanks for your help its greatly appreciated.