I always use public transport to gigs.
So the following is a better option for me.
Tilbury to Gravesend ferry service
A regular ferry service operates from Monday to Saturday between Tilbury riverside and Gravesend.

Check the Tilbury to Gravesend ferry timetable.

Fares

Ticket Type        Adult        Child
Single, any time        £4        £2
Day return, peak time        £5        £2.50
Day return, off-peak        £3        £2
Saver 10        £22        £11
Travel is free at any time for holders of a Thurrock, Kent or Medway National Concessionary Bus Pass. Other National Concessionary Bus Pass holders travel free between 9:30am and 11pm, Monday to Friday, or at weekends – at other times fares will be charged at the child rate for a single or return.

When buying ferry tickets:

peak time fares apply from 5:40am to 9:15am and 4:15pm to 7:10pm
off-peak fares apply at all other times
Saver 10 is a weekly ticket that allows passengers to buy one ticket for 10 trips – either peak or off-peak – in advance of their journey, which saves both time and money
child fares apply to children aged 5 to 15 years-old
children under the age of 5 can travel free of charge at all times provided they are accompanied by a fare-paying passenger
no more than 4 children under the age of 5 can accompany each fare-paying passenger
tickets must be purchased on the ferry itself
The Tilbury to Gravesend ferry is a foot passenger service. Bicycles can be taken on board, but motorbikes and other types of vehicle are not permitted.