File picture: Hamad I Mohammed / Reuters.

London - Williams replaced its head of aerodynamics, South African Dirk De Beer, on Wednesday after a troubled start to the Formula One season that has left the former championship winning team languishing in last place with only four points from six races.

The team, which has the same engines as championship leader Mercedes, said in a statement the South African had stepped down with immediate effect.

Dave Wheater has been handed De Beer's title, while chief engineer Doug McKiernan assumes responsibility over the aerodynamic and design direction of the car.

De Beer's departure followed that of chief designer Ed Wood, who left earlier in May for personal reasons.

This year's FW41 car has disappointed in the hands of Canadian teenager Lance Stroll and Russian rookie Sergey Sirotkin.

The car had been presented in February with technical head Paddy Lowe saying the team had "pursued a very different aerodynamic concept which has allowed us some significant progress in aerodynamic performance".

However Williams failed to score a point until Stroll finished eighth in Azerbaijan at the end of April, and that remains the only race in which it had scored.

Stroll finished two laps down and last of those classified in Monaco at the weekend, while Sirotkin was one place ahead of the Canadian in 16th.

De Beer joined from Ferrari last year and was previously at Sauber, Renault and Lotus. McKiernan joined from McLaren, where he was head of aerodynamics, earlier this year.

Williams was the only team other than Mercedes, Ferrari and Red Bull to have a driver on the podium last year, with Stroll third in Azerbaijan, but have not won a race since 2012.