Adjusting the mast: secrets of diagonal shrouds

Shrouds adjustment is a job that should be done by a professional rigger, as it is a delicate operation for bothmast safety and boat performance. In entrusting a job to a professional, however, it is advisable for a shipowner to be clear on what some basic concepts are, so that in the future he or she may also be able to work independently on his or her own mast.

Vertical and diagonal partitions

Let’s start with a concept, on the masts of cruising boats or performance cruisers, there are usually two types of shrouds, the vertical and the diagonal. The former are, simplifying, the longest and outermost shrouds, which go from the deck to the masthead or stop a little below, depending on the type of rigging.

These have as one of their functions, if the rig includes quartered spreaders, to give preflection to the mast. Cocking the shrouds high in fact will bend the mast toward the stern and consequently move the mainsail grease forward. All masts, even racing masts, are adjusted so that they always have a minimum amount of pre-flexion, which will be greater when we have to sail in strong winds.

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The secret of diagonal shrouds

Less intuitive, however, is the function of the diagonal shrouds. These have compression tasks and help to limit the movements of the mast especially in its middle and lower parts. In fact, they prevent the curvature of the mast from falling too far downwind and limit its so-called “pumping” on the wave.

However, diagonals also need to be adjusted carefully and methodically. The more bullshit the verticals are, the more unloaded the diagonals will be and vice versa. So if, for example, we decide that for a light wind outing we will drop a few turns of tension on the high shrouds, we will need to check what happens to the diagonals. These will increase their tension and must be let go at the same rate as the high ones; in fact, the two settings are linked.

Adjusting the diagonal shrouds

On diagonal shrouds, little tension is sufficient: in fact, just pin them down so that they take more load when the mast is under pressure and not before. This is because the mast, in medium-light wind, if we look at it from the boom attachment toward the pen should have a precise shape. In addition to the bow-aft pre-flexion, which in light winds should only be hinted at, it should have a slight bend to leeward.

The right curvature

This slight curve serves with little air to help sail shape and seek power. As the wind rises this curve will have to be gradually less present because we will correct it by adjusting the tensions, but it must never reverse. We must not have the tree with a curve toward upwind, it means the diagonals are too tight.

If the tension is correct, when we sail upwind we will see the leeward diagonals in the notice: let us not be frightened, at the moment of tacking these will go on load without any problem.

Mauro Giuffrè

• Read also: Adjusting the tree in high winds