This varies on a combination of the following: tides, boat, distance, heating etc and unfortunately it’s not possible to estimate before your holiday begins. The engines are designed to be most efficient at the normal cruising speed so to conserve fuel you should always stick to, or go slower than the speed limits, which are generally between 3 mph and 6 mph. This will avoid riverbank erosion and also allow you to enjoy the wonderful constantly changing scenery and wildlife. You are advised to take advantage of the tides on the lower reaches of the river Bure and Southern rivers, check out the Broads Authority tide table
to find out more.