Members of the Churchill family were aboard the Havengore, which travelled to Westminster in central London.
Earlier, Prime Minister David Cameron laid a wreath in memory of Churchill, who, as prime minister, led Britain to victory in World War Two.
A service will also take place later at Westminster Abbey.
Speaking at a service in Parliament at the start of a day of commemorations, Mr Cameron said Churchill would be remembered as a "great leader and great Briton".
"If there is one aspect of this man I admire more than any other - it is Churchill the patriot," he said.
Mr Cameron said the UK needed to draw on the "courage and resolve" of Churchill to battle "every affront to freedom in this century". (+ BBC videos) » | Friday, January 30, 2015
