Just to clear this up.
Racing rowing boats have special dispensation under Road vehicles regulations 1986, regulations 81 and 86, schedule 12, which allows up to 3.05m overhangs with end markers (the red rags) to be carried without escort or prior notification.
The load on the car is 2.85m ovehangs (I measure every time) so is legal. There are exceptions to this though, such as parts of London, where the total length is limited to 10.98m and the overhangs cannot exceed 2.6m without police premission.
It gets some looks, but have never been pulled (yet!!!). Alway carry a copy of the legislation just in case.