A clean hull enables your boat to run as efficiently as possible but how much can you actually save? MBM finds out...

It is common sense that fouling on a boat’s hull will lead to increased resistance, which basically means you are going to burn more fuel for every knot you make. The outcome is compromised efficiency and a poorer mpg figure than with a clean hull, but by how much?

To answer this question we undertook some comprehensive seatrials in a 10-year-old Princess 430 installed with twin Volvo TAMD63P engines rated to 370hp at 2800rpm, measuring its performance before and after its spring lift, scrub and antifoul.

Fuel efficiency | Practical advice | Motor Boats Monthly |

The performance table tells the full story but, in short, the boat’s increase in speed for the same revs averages out at around 13%, as well as an overall reduction in fuel consumption.

The result is that the all-important measure of efficiency – miles per gallon – jumps by around 25% with the cleaner hull. Even better, at the boat’s usual 2400rpm cruising rate the mpg figure is a massive 30% up.

Pre scrub figures | Fuel efficiency | Motor Boats Monthly |Post scrub figures | Fuel efficiency | Motor Boats Monthly |

With these figures in mind it makes good sense to try to grab a scrub before setting off on any prolonged cruise.

During a two-week, 600-mile round trip the owners of this Princess will save a couple of hundred quid with a clean hull, and it will make faster passages without pushing the engines harder than is necessary.