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Know your mast

The mast is the backbone of the sail and, just as in a human body, is the core of its proper functioning. Any body, even the most trained one, cannot express itself in an athletic gesture if its spine is not functioning properly!

Choosing a mast with high mechanical characteristics is the most important step to obtain the best performance from your sail.

How to mount it

The mast must be mounted in order to make the most of the potential of the sail. Start by following the directions on the sail bags. Don't dwell too long trying to replicate the numbers exactly. Often in fact, the measures converted from a different metric system may not be completely accurate, as well as the starting points of the scales shown on the boom or extension, may vary from brand to brand.

Fortunately today almost all brands of sails are used to put visual indications on the upper part (leech) of the sail, indicating the maximum point beyond which the sail must remain taut.

Adding centimeters of downhaul other than suggested leads to a flatter profile in the central part and a more open sail in the leech; in this case it is likely to be necessary to remove centimeters of clew from the boom. The thrust center in this way moves forward, towards the mast. A sail so tense is less reactive and more likely to withstand strong winds. The opposite happens if is given less downhaul tension than recommended.

Check your mast

Always check that the plug-in in which the mast is inserted and its internal part are clean. A plug-in dirty with dust or sand is a sure cause for the two halves to interlock. Our masts are by far the ones with the most precise grafting tolerance. The advantage: having a mast without backlash, obtaining a more efficient transmission of efforts and having less chance of grafts remaining bent.

A tip is to apply adhesive tape around the joint after joining the two parts; this prevents sand from getting inside, causing the problems described above, and that, during the assembly of the mast in the sail, the top and bottom move away, even by a single centimeter. An event that occurs frequently without us noticing, causing an almost certain break in the central section.

Once the mast has been inserted into the sail, slide your hand over the sail bag at the middle, to check that there are no gaps, even minimal, between the base and the top.

If the mast gets stuck, before asking friends for help, make it vibrate by keeping it horizontal and holding it with one hand at both ends. Then strain it, turning it in the opposite direction from both ends. The next step is to use two booms, one in the lower part and one in the upper part, to take advantage of the leverage and make more strength. A further and last possibility is to remove the cap from the end of the top, insert a hose of water and repeat all the operations described by making the water flow inside the section to dissolve the salt and sand encrustation that is the cause of the blockage.

Watch out for the sun

Carbon is affected by heat rather than UV rays. On a very hot day, the mast surface temperature can exceed 80 degrees (we measured it). If you leave the mast mounted and tense, tensions can be created at the points of maximum effort (generally between 70 and 90 cm from the base) or in the upper part where there is the greatest deformation, capable of causing it to collapse. It is always recommended to disarm the equipment and not leave it exposed to the sun. This operation is critical when using SDM masts, which are thinner, have a greater exposed surface and 3 times higher load tensions.

* Note: An SDM mast, which is pulled by an 8 pulley hoist (4 eyelets depending on the sail), is subjected to a load tension equal to 8 times the one applied by hand by pulling the top of the downhaul.

Mast adjustment

Each sail has a specific mast length to reach the required luff (total length), which in turn is obtained by adding the necessary centimeters with the extension. Some sails on the market adapt to two possible mast sizes by varying the length of the extension to obtain the same luff as well as being able to play by mixing different base and top (with the top in the immediately following longer length). For example, if we have a 435 cm luff, we can use a 430 mast with 5 cm of extension or a 400 with 35 cm of extension or by inserting the base of a 400 and the top of a 430 with 20 cm of extension. In the latter case, remember to never mix bottoms and tops of different models with different percentages of carbon.

Even if the curves obtained may be similar, the perceived behavior in navigation is definetly different. In fact, luffs of equal total size are obtained, but with different profiles, which influences the sail and therefore the reaction perceived by the rider. There is no absolute best or worst: the rig is made up of the height of the rider, the type of board, the fin (s) used and the conditions in which you set sail. A longer mast with higher BMI is more stable in high wind conditions and is still preferred by tall, heavy athletes. Exactly the opposite happens in the case of a shorter mast. These are general indications, the best thing is to try in the same conditions, different setups.



Let's start with literature. Then we will then try to explain the "behind the scenes".

IMCS is a dimensionless value, which indicates, in a certain way, the stiffness of a mast based on its length compared to a standard mast of 460 cm. It comes from a dated formula, but still used by sail manufacturers. It also indicates the depth of the arrow in the middle of the mast under a load of 30 kilos. The value increases as the mast size increases, indicating greater stiffnesses as the mast length increases. The IMCS values ​​for each length are quite similar between different brands and usually vary a maximum of one point from the values ​​shown here.

340 (15), 370 (17), 400 (19), 430 (21), 460 (26), 490 (29), 520 (33)



The IMCS is associated with two other values ​​that determine the "profile" of the sail. These are the percentages of deflection (or curvature) that a mast undergoes at ¼ and ¾ of its length, compared to the maximum deflection value reached in the center, under a load of 30 kilos. The value at ¾ usually varies from 74 to 79% from to the central value, that at ¼ from 62 to 65%. The curve thus defined and the numbers, have a relative sense, if associated with a value of IMCS, since, it must be underlined, they are percentage expressions compared to the bending in the center which is precisely the value IMCS. For convenience, it was decided to define 3 types of curves depending on the value assumed by the difference in the percentage values ​​of top and base:






The mast and the so-called perfect measures 

Although these numbers are useful for sailmakers and builders like us, to start defining the mast of a given sail, they represent only a part of a mast project and not even the most important one.

The shape of the mast. Curves and IMCS

All the IMCS and Curva values ​​mentioned above, are not used as a percentage by the designer, but converted into metric system measurements, namely millimeters. If we grouped all the masts from the hard top to the flex top ones with the system used today, we would observe differences that are within 20 millimeters between one curve to another. Whereas, however almost every modern sail is constant curve, the difference is within 10 millimeters! In addition, carbon, in its workable form or the pre-impregnated, has mechanical tolerances in which they are translated into variations on the curve tolerances. The quality control on each mast carried out in Reglass certainly excludes what is out of tolerance. However, differences of one percentage point are generally accepted and are within the technological limits.

The current measurement system, even if it could be precisely translated, defines a deformation that is the result of an applied load that is not real compared to what the mast will then undergo during use (no mast is "pulled" with a weight from the center, nontheless with 30 kilos!). 

Finally, two masts even with the same curve, if they differ: in material, diameters and shape, they can make the sail take on two different shapes and behave differently in the water.


The shape of the masts

Basically, masts with different profiles can have the same curve. It is evident that a mast with a cylindrical section with greater lenght compared to another with a more pronounced or thinner taper in the pen will have a totally different dynamic response even thought it is designed to have the same curve as a mast with a different profile. We cannot say if it is better or worse. It's simply different. As mentioned above, a lot depends on the rig as a whole, including build and navigation mode.

The material

The indication: 100% carbon fiber mast is not a indicator of its quality level, it simply means that there is no (or shouldn't be!) glass fiber inside. In fact, there are different types of carbon with different mechanical characteristics. What makes a composite product better than another depends not only on the type of material used, but on the entire production chain: from the choice of fibers to the preparation of the resins with which to make the pre-impregnated and to the numerous operations through which, in every single phase, a mast is built. These operations represent real industrial secrets: company know-how, the result of mistakes and successes that make a huge difference between similar products manufactured by different companies.


Reglass was the first company in the world to use composite to make windsurf masts and is also the only company in the sector that manufactures the pre-impregnated in-house. In this way it is possible to have absolute control over the production and customize the product, choosing, among the different "recipes" - sometimes elaborated with minimal but substantial differences - the one most suitable for the final use of the composite.



In the past, different brands actually had very dissimilar curves between their sails and the masts could rarely interchange. Now no longer. The sails that mount constant masts, even with the relative differences, are the majority. What can enhance the efficiency of a sail today is therefore not only the percentage of carbon in the mast, nor even the "perfect" curve. The latter, as we have seen, comes from a test that provides for a load, not corresponding to reality, of only 30 kilos (when instead peak loads of a few hundred kilos are involved) and from obligatory tolerances that deviate the values ​​from to the expected result.


The difference, sometimes a true quantum leap from a technical point of view, between one tree and another, basically comes from the construction process, starting with the way the fibers are impregnated with resin, the type and quantity of resin. used, finally: by the times and methods in which the tree passes through the various and numerous construction phases. Two identical trees produced by two different companies will have different mechanical and qualitative responses. The technology and know-how of a company that has been producing composite for over 30 years such as Reglass, translates into advanced technology and very high shaft performance. The main task of which is to maintain the most efficient profile of the wing under load, to return it to its position of maximum aerodynamic efficiency when it moves away from it and to distribute the efforts in the most harmonious way possible along its entire profile.


In the abused metaphor of the vertebral column, this has not only the task of supporting the muscles but and above all, that of giving precise, fast and coordinated signals to make the movement perform as efficiently as possible.


A mast built by Reglass is all of this.

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