Svitzer London

It's a tug, as can be seen...
You see a lot of tugs from Gravesend: Svitzer has a base just down river where several more are moored and there are 6 - 8 on the river, usually, plus a second company, KOTUG, operating another fleet. The tugs can often be seen pulling and pushing huge car carriers around across the river at Tilbury Docks. There are endless smaller, older tugs to be seen.