Thanks bob, that's made it a lot more clearer with regard to the workings of the canal.

Tankers are subject to a speed limit of 14 km/h (7.6 knots) while the limit for ‘ordinary’ vessels is 16 km/h (8.6 knots). So, when there a lot of tankers for a convoy, they tend to go through together, after the other ships.

So when transiting the Suez canal do the convoys consist of the same category of vessel or is it a mixture? Example, a crude carrier combined with general cargo vessels etc or all oil tankers?