TECHNIQUE Adjusting shaft deflection to go faster

If you want to make your boat run more, to get some good satisfaction out of racing and have fun cruising as well, you’ve come to the right place. We will reveal all the tricks together with Phi!Number experts. In the chair, for the first three lessons related to the search for maximum upwind speed, rises Roberto Spata, one of the most successful sailors on the race courses and owner of New Wind: we will discover how to adjust the mast and how to interpret all the “signals” our boat sends us. In the first introductory episode, we talked about the parameters (boat pitch and mast adjustment and sail shape) you need to know to increase your boat’s performance. Today we go down to specifics:

HERE YOU WILL FIND THE FIRST EPISODE

Upwind speed: mast adjustment and preflexion

Some theoretical background: sails as the wings of an airplane

Just as different profiles of a wing would make an airplane fly in different ways, so too can sails make us sail more or less well depending on their shape. A military fighter flying at high speeds needs thin wings with less friction, while a heavy, slow airliner will need thicker airfoils to maintain lift.

The engineers who designed these wings took into account a number of common and necessary factors to achieve the optimum efficiency for the two types of requirements, and as shown in the pictures, there are virtually identical benchmarks between an airplane wing and a wing profile.

These parameters are also very similar from a geometric point of view: if certain proportions are not met, an airplane will fail to fly or at least have a lot of difficulty in doing so, just as a wing will lose its efficiency.

The parameters of a sail: C – D – X

With reference to the legend shown, the letter “C” represents the chord, that is, the straight-line distance from the luff of the sail to the leech. The letter “D” is the maximum depth of the sail (in short, how fat it is, camber) and is expressed as a percentage of the chord. Finally, the letter “X” represents “the position” of the camber relative to the string(draft) and is also expressed as a percentage relative to the string. Well, the first basic assumption for achieving an efficient sail is that the draft should never be more than 50 percent aft of the chord. And this is in all wind conditions.

What does that have to do with shaft adjustment?

We know that any mast, viewed from the side, has its own pre-flexion modified essentially by the tension of the shrouds passing through the head of the spreaders. These in fact, again from a side view, are not perfectly parallel with respect to the mast but have a certain angle toward the stern called the neighborhood.

With a fresh wind upwind, due to the increased pressure on the sails the loads on the rigging would increase and at the height of the spreader attachment on the mast-essentially the fulcrum where the loads converge-the force pushing the mast toward the bow would increase resulting in a marked increase in deflection. This would have the effect of increasing the chord with the unfortunate consequence that the position of the maximum sail depth(draft), as shown in the pictures, would shift more than 50 percent. With this configuration, the sail would almost totally lose its efficiency.

Another devastating consequence of excessive bending-in terms of performance and ease of conducting-would be the effect of backstay tension or steering wheels. In fact, as the wind increases we know that we should increase the load on the backstay(s) to decrease the forestay catenary so as to thin the headsail. However, both backstays and flywheels not only exert a pull horizontally toward the stern, but also exert a powerful downward pull that further contributes to the deflection of the mast: thus the forestay attachment on the mast is lowered and consequently the catenary on the forestay is increased.

Checking the preflexion

The pull toward the bow at the spreaders and the resulting 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 and diagonals.

Such opposition of forces is essential to manage the upwind behavior of the mast, in fact the correct adjustment of the low and diagonal shrouds will allow us to have a stiffer structure especially in the lower and middle parts.

Consequently, by hollowing out the flywheel or backstay, only the upper part of the mast will be flexed, where, among other things, the forestay is also attached, thus obtaining a twofold effect: on the one hand, that of slimming and opening l‘exit of the upper area of the mainsail (resulting in depowering and giving the boat less heeling action and the greatest possible efficiency in sustained winds), and on the other that of more effectively reducing the catenary of the forestay with the effect of slimming the profile of the sail itself. Both of these factors contribute to reduced boat heel which, as we have seen, contribute to easier upwind handling and keep the boat fast and buoyant.

Weapon with steering wheels

Absurdly, fractional masts armed with flywheels may be easier to adjust in navigation since they also generally possess a pair of low flywheels that, by exerting a greater pull toward the stern, act as a direct regulator of mast deflection. However, for the sake of greater convenience in navigation, this type of rigging is now very rare.

This is why it is so important as the wind strength changes, to change the tension of the shrouds on the masts with the spreaders quartered and the backstay alone: this counteracts the variation in the buoyancy at the height of the spreaders, which generates more chainmail and an incorrect mainsail shape.

For cruising, even 2 or 3 adjustment steps can make a difference. It seems impossible, yet I guarantee that several times during my career I have boarded boats that, due to incorrect mast trim, already in medium air were forced to reduce sails early, solving only part of the problem of excessive heeling.

Subsequently, as a result of proper set-up, we were able to carry the same sail even in 5 or 6 knots more wind intensity than in the previous setting, and with an impressive improvement in ease of handling and reduction of heeling.

IN THE NEXT INSTALLMENT: LURCHING AND SHAPE STABILITY

…CONTINUED…

PHI!NUMBER AND ITS EXPERTS
Phi!Number, an Italian company for over 10 years dedicated to fine-tuning sailing projects with numerous achievements at the international level, has a mission based on three key points: first, reaching the top of the rankings, then the technical growth and enjoyment of the owner and his team, as well as the right choices and better budget management and optimization. How? Drawing on the cooperation of the best sailors and experts to optimize every aspect of boat, crew, logistics, sponsor management and suppliers.

In collaboration with the Giornale Della Vela, Phi!Number presents a periodic review of the topics that are fundamental to determining a real leap forward in sailing. We begin with the tricks to more easily and quickly steer one’s boat upwind through mast adjustment. The “prof in the chair” for this cycle is from one of the leading experts in the field: Roberto Spata, former owner of New Wind and multiple European and world champion in various classes. There are some certainties in the sailing world: those who have frequented the race courses know that one of them is that the boats where Roberto sails are faster. www.phi-number.com

WE ARE CREATING THE JOURNAL OF SAILING SAILING TEAM! DO YOU WANT TO BE PART OF IT?

I want you! Would you like to participate in a racing season with an optimized race boat, alongside Phi!Number’s true professional champions on board? Nothing more than a project like this will allow you to grow technically by participating in the most important offshore and between the buoys events in Italy in 2020!

The boat is the bomb: Cheyenne, a race-prepared Rodman 42 that has been featured on the offshore courses and between the buoys in recent seasons And not only that, you will be able to attend free educational appointments and technical lectures on sailing-specific topics (regulation, setting, communication, mental, etc.) given by Phi!Number experts! Selection is open.

HOW TO PARTICIPATE (WITH LOTS OF DISCOUNT)
If you are up for the challenge and want to get involved write now for information and reservations to: info@phi-number.com! If you write VELASAILINGTEAM in the subject line of the email you will automatically get a 10% discount on the program registration fee!

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