The Marchioness disaster was a fatal collision between two vessels on the River Thames in London on 20 August 1989, which resulted in the drowning of 51 people. The pleasure steamer Marchioness sank after being pushed under by the dredger Bowbelle, late at night close to Cannon Street Railway Bridge
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.
The dredger Bowbelle collided with Marchioness in the early hours of 20 August 1989. At the instant of collision the anchor of the dredger cut through the side of Marchioness, which capsized and quickly filled with water, while being pushed under by Bowbelle. As 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 Bowbelle as "hitting it [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.
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