The Marchioness disaster was a fatal collision between two vessels on the Thames in London on 20 August 1989, which resulted in the drowning of 51 people.
The pleasure boat Marchioness sank after being pushed under by the dredger Bowbelle, late at night close to Cannon Street Railway Bridge. A formal inquiry blamed poor lookouts on both vessels, and inadequate instruction of both crews. Four new lifeboat stations were later installed on the river.
The Marchioness was a pleasure steamer built in 1923 and was one of the little ships of Dunkirk in 1940.
On 19 August 1989, the boat was hired for a party organised by photographer agent Jonathan Phang to celebrate the 26th birthday of Antonio de Vasconcellos, who worked in a merchant bank. The pair were good friends and business partners in a photographic agency.
The dredger Bowbelle collided with the Marchioness in the early hours of 20 August 1989. At the instant of collision the anchor of the dredger cut through the side of the Marchioness, which rolled over and quickly filled with water, while being pushed under by the Bowbelle. As the Marchioness capsized, her entire superstructure became detached.
The formal investigation put the time elapsed, from the instant of collision at 1:46 a.m. to complete immersion, at close to 30 seconds. Witnesses quoted in that investigation described the Bowbelle as "hitting it [the Marchioness] in about its centre then (mounting) it, pushing it under the water like a toy boat.
Of the dead, 24 were recovered from the sunken hull. Most of the survivors were on the upper decks at the time of the collision.