By Ian Budgen One of GBR Challenge's trimmers explains his onboard role

Budgen: Trimmers have to look after their grinders

My job is upwind trimmer which means I look after the sail shape of the genoa while going to windward.

I sit by the primary winch down to leeward which generally means when it is windy and wavy I get completely drenched - it is like someone turning a fire hose on you. It is pretty wet and pretty exciting.

Because the sails are so large there is a huge amount of load on the sheets so we put five or six turns around the primary winch which is about 18 inches in diameter.

We keep a constant hold on the sheets and can ease them ourselves.

But when we want a sheet wound on, that is when the grinders come in to their own.

The trimmers have to be very good friends with their grinders. The relationship is really important.

It is not uncommon for trimmers to buy their grinders presents and drinks to keep them on side because the grinders can make you look very stupid as a trimmer.

We also have a range of hydraulic rams, operated by pumps, which adjust the shape of the sail.

We can either adjust the jib tack (the front bottom corner) to change the luff (front edge of sail) tension;

Or we can alter the clew (back bottom corner) inboard or outboard or forwards and back to change the sail shape from being full in powered up conditions to a fatter, more twisted sail for when it is fresh and wavy.

Trimmers holds the sheets that control the sails

You have to have a good eye for sail shape and knowledge of what shape is fastest in varying conditions.

And you have to have a good level of concentration in order to get the best out of the sail for as long as you are going upwind, which during testing can be as long as two hours on the trot.

Downwind, I take the spinnaker guy which is the rope attached to the outboard end of the spinnaker pole.

I have to keep a constant eye on the position of the guy while the trimmer on the leeward side plays the spinnaker sheet.

Coordination and team work between the two trimmers is important so that the spinnaker is set effectively.