Nearly all boats will have a 12 Volt system installed. To have a 240 Volt system you have a number of options, Inverter, Landline or Generator.
a) Landline: A connection to plug in at a marina, when an electric supply is provided.
b) Inverter: This is a devise that converts your 12 Volt battery supply to a 240 Volt supply for domestic use, an average price will be in the region of £100 to £4000, but is dependant on size.
c) Generator: Either a petrol, gas or diesel generator will give you a 240 Volt supply. Prices vary considerably with a petrol generator costing in the region of £400-1200, while a diesel one will cost around £1,500 to £4,000.