fly from outside of china to Beijing, stay for less than 144 hrs, depart on the cruise ship from Tianjin to third country or area, You can transit China visa free, provided you hold an approved passport, and Beijing/Tianjin is your only stop inside China.
You will get a stamp in your passport and since you will have legally entered mainland China and have no other stops in mainland China (Hong Kong is a separate entity from mainland China), you will not need a visa and therefore the cruise line will not care if you have a China visa or not.
You need to have documentation that shows you have a confirmed space on your cruise ship that departs within 144 hours of arrival in Beijing for when you board the flight to Beijing and to show Beijing Entry Immigration when applying for the 144 hour Transit Without Visa (TWOV).
The TWOV policy for Beijing can be read here: http://en.bcia.com.cn/server/notice/144visafree/144visafree_policy.shtml