Drop everything! We skid less by adjusting the shaft

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After telling you about the importance of a balanced and easy-to-lead boat (Read HERE, HERE, HERE, HERE), we introduced HERE another important topic: mast adjustment.

In fact, as mentioned in the previous installment, it is not enough to adjust the sails in the correct way; as the weather conditions change, the tension of the shrouds and the resulting profile of the mast becomes crucial.

As the wind increases, due to the greater wind pressure on the sails, the loads on the rigging and mast increase, and it therefore happens that at the height of the spreaders, basically the fulcrum where the loads converge, a force is created that pushes the mast toward the bow, resulting in a marked increase in mast deflection. This buoyancy toward the bow, and the consequent increase in mast deflection, is therefore proportional to the load on the mast and thus to the wind intensity.

And what happens to our sails?

The mast went toward the bow due to excessive pre-bending, the chord stretched with the unfortunate consequence that the maximum depth of the sail, went beyond 50 percent of the chord, thus well beyond what is allowed for having a well-tuned and efficient sail. With this configuration, an airplane has serious difficulties in flying, and a glider almost totally loses its efficiency. The second devastating effect of excessive pre-bending is the effect of backstay or staysail tension; as the wind increases, we know that we have to pull the backstay or staysails to decrease the forestay catenary to thin the headsail but both backstay and staysails exert not only a horizontal pull towards the stern but also a strong downward pull that contributes, if the rigging is not touched, to further increase the mast pre-bending by falling back into the unfortunate situation mentioned above.

The shaft also flexes too much in its lower part

But how then can we reduce the preflexion?

This forward thrust of the mast at the level of the spreaders, and the consequent extra deflection of the mast, can be counteracted by increasing the tension of the shrouds in general but especially, with due proportion, by the only part of the rigging that exerts a pull toward the stern: the low shrouds.

The effect of the tension of low shrouds

Such opposition of forces is crucial because: the mast, if properly adjusted, possesses a much stiffer structure as the wind increases, especially in the lower and middle parts. As a result, by cocking the steering wheel or backstay, it only flexes the part high of the mast, where by the way the forestay is also attached.

The effect of steering wheels

Thus, by caulking the headstay or backstay, a twofold effect is achieved: it only modifies the output of the upper part of the mainsail, which, by opening and shedding, is depowered and gives the boat the greatest possible efficiency in sustained winds, and at the same time it more effectively reduces the catenary of the forestay, with the effect of shedding the profile of the headsail. Both of these factors contribute disproportionately to reducing the boat’s heeling. Absurdly, fractional masts with flywheels may be easier to adjust in navigation since they also generally possess a pair of low flywheels, which, by exerting a greater pull toward the stern, act as a regulator of the mast’s pre-flexion. But we know that, for reasons of greater convenience in navigation, they are disappearing from circulation.

This is why it is so important, especially on trees with aquartiered spreaders and backstay only, change the tension of the shrouds for each wind range to counteract the variation in the buoyancy on the mast at the height of the spreaders, and the consequent variation in pre-bending, as the wind strength changes. For cruising, even 2 or 3 adjustment steps can make a difference. It seems impossible, doesn’t it?

Yet I guarantee you that several times during my career I have boarded boats that, due to incorrect mast setup, already in medium air were forced to reduce the headsail early, solving only part of the problem of excessive heeling while later, as a result of correct mast setup, we were able to carry the larger sail even in 5 or 6 knots more wind strength than in the previous setting and with an impressive improvement in ease of handling and reduction of heeling.

Clearly, however, there are boats that are more inclined to have a greater heel but this depends essentially on the shape and weight of the keel and the water lines of the boat. For example, there are boats that have a limited keel weight but thanks to a stability coming from the hull shape are able to have limited heeling; conversely, there are boats that have a hull shape that is not very prone to righting and that need a more generous keel weight in order not to heel too much.

In the case that achieving such a balance is not possible, it is rather difficult to think of reducing the heeling without making substantial changes, especially on keel weight, but before doing so my advice is to follow, in addition to the mast setting illustrated above, some small tricks that, it seems impossible, can increase righting and decrease heeling even substantially: Lower all “unnecessary” weights or that are at any rate rarely used; this contributes to lowering the total center of gravity of the boat contributing to increase righting. Same in eliminating, as much as possible, unnecessary weights from the extreme bow and/or stern, placing them amidships and as low as possible; this way the boat will pitch less and righting will increase.

If the above is not enough, sometimes significant improvements can be made without changing the keel, putting some lead loaves, the weight of which depends essentially on the characteristics of the boat, in the bilge between the madiers that make up the structure of the bottom of the boat and the keel attachment: these are very low weights that also contribute to lowering the total center of gravity of the boat and increase its righting.

ROBERTO SPATA

Class of 1962 from Como. Laser National until 1983, he then approached offshore sailing by racing on any type of boat and specifically in the IOR, IMS, Maxi Yacht, One-design, ORC and IRC Classes in the roles of tactician, helmsman or mainsman, often taking care of sail and boat tuning.

From 1988 to 2000 he worked with North Sails and continues to have technical relationships and with all the sailmakers, designers and shipyards also as a project manager.

 

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