Graduate Dinghy Association

Grad Tuning Tips 2

by Adrian Baker

The rig is the 'engine' of your boat and the controls are the 'gears'. Of course, it would be nice if one's boat had an automatic gearbox, but instead we are stuck with lots of bits of string and cleating devices. Knowing how to use the controls is important if you want to go fast in all conditions, and on all points of sailing.

Most Grad sailors who have been doing the circuit for some time will have their own individual theories of how to set up their boat, and which string to pull and when. In fact, with practice, turning a mark and moving on to a new point of sailing sounds little alarm bells with me which say 'look at the rig and pull some strings'

The principal controls which govern speed affect the mainsail shape. The interaction of main and genoa is important, but generally there's not much one can do when sailing to alter this relationship, apart from pulling in the sheet a bit harder, or releasing it a fraction.

Sheeting points can be set up at the start for any particular wind strength, by reference to the luff telltales. The interesting bit is the mast, which is bendy; the mainsail, which is stretchy; and the controls which tension the edges of the sail and affect the straightness of the mast. So how much one pulls (tensions) the controls and which ones at which time is the real secret. The principal things which one can play, and how they affect mast and sail shape, are as follows - remember that generally a full sail equals more power; flatter sail equals less power.

Mast Prebend

This is the lower to middle mast bend, induced by rig tension and controls mainsail fullness in the lower two-thirds of the sail. Prebend is largely controlled by the degree of spreader 'sweep back'. More sweep = more prebend; less sweep = less prebend. The case with which this can be achieved is dependent on basic spar stiffness and position of the jib halyard sheave box relative to shroud pin position, the greater the distance the easier it will be to bend the mast. These positions are normally fixed and out of our control but there will be differences on different masts. So, to achieve a given measured amount of prebend, two different masts may require different degrees of sweep back.

 Kicking Strap

The kicker is used to control mainsail leech tension, it also has the affect of bending the topmast above the shrouds as tension increases. This consequently flattens the upper third of the mainsail very effectively and has a decreasing effect downwards.

 Outhaul

This affects the mainsail fullness, particularly in the lower third, it also affects the 'cup' to windward in the leech - a feature which can help pointing in some conditions.

 Cunningham

A luff tensioning device, used to control horizontal wrinkles in the mainsail near the luff following mast bending. Tensioning the cunningham pulls draught forward and relieves leech tension, which can be beneficial in strong winds.

Tensions Table

Tension Rating:- (no not nervous tension, but looking at the chart it could be!) : 0= no tension to 5= lots of tension

Points of Sailing:- B=Beating/close hauled; R=Reaching; Ru=Running

 

   

Light Airs

Light - Mod

Moderate

Mod - Fresh

Approx Wind Force

1/2 - 1

1 - 2

2 - 3

4 - 5

Controls

Points of Sailing

B

R

Ru

B

R

Ru

B

R

Ru

B

R

Ru

Prebend (rig tension)

5

4

2

3

2

2

2

1

0

4

2

2

Kicker

1

2

1

2

3

2

3

4

3

4

5

4

Outhaul

4

3

4

3

2

3

2

1

3

5

4

5

Cunningham

0

0

0

1

2

0

2

2

0

4

2

0

It would be interesting to hear if this table works for others