Ships periodically require surveys, which are inspections a lot like your annual car inspection, though a lot of states don’t have them anymore. Key systems of the ship are checked for compliance with safety rules and such things as pollution control equipment. The inspection period for most ships is I believe 5 years. Major surveys occur less often, but result in substantial repairs most of the time. Voyages on the open sea put a great strain on ships’ mechanical structure.
Repairs of any problems must be made before the ship can sail again. Today most surveys are done in China. See the article for the dominance of China in this market.
Covid quarantines for ship surveys are very strict and expensive. China has maintained recently a zero new infections rte for those arising internally. However there have been a few infections from travelers entering the country. That is why the strict regime is being enforced. Ships are a frequent source of infections; the mariners are exposed for a long time, air circulation is not very good in the interior, and mariners are travelers likely to be exposed to new people wherever they land.
So don’t take your ship to China for your survey work.

Sam Chambers August 30, 2021
Owners urged to carry out surveys outside of China as tough new quarantine measures come into place – Splash247
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