Buying a mast can be confusing. On this page we aim to simplify things, give advice, and outline the theory behind mast bend curves, response, and construction. Our objective is to help you choose the right mast – enabling you to maximise value, and enjoy your ride for several seasons of performance and durability.
PUT YOUR MONEY WHERE YOUR MAST IS
The first thing to know about mast choice is how important it is! The mast is the backbone of your gear. All the forces from your sail, the vibrations from your board and all the effort that you put in, they all come together in the mast. A mast that doesn't match your sails and/or your own preferences will ruin your day.
Trust us. Get it right first time and you’ll enjoy amazing, long-lasting value for money from your mast. And not have to worry about trading them for the latest model each year.
Also, although we hope you gain insight from reading this, we recommend going to your local dealer for expert advice and service. Their input will be more complete than what we can offer in this basic guide.
MAKE A MATCH
A vital aspect of optimum sail trim is the mast you choose - in combination with the correct downhaul and outhaul.
It’s considered good practice to follow the mast type and length recommendation of the sail manufacturer. The safe choice is to buy your mast and sails of the same brand, as they developed the sails around that mast. But many sail brands use similar mast specs, so mixing and matching across brands is sometimes a possibility. You may also consider buying an independent brand (yes, such as Unifiber!) which often works just as well.
Our MAST SELECTOR will help you to make the right choice. The specs are based on the averages from all the brands we’ve measured over the past seasons. You can never record enough data and we’ve measured a lot of masts over the years! The result is a reliable tool that we and our customers have full confidence in.
THREE EASY STEPS
The key elements to consider when choosing a mast are:
- Carbon Content
- Bend Curve
First, let’s look at Carbon Content.
HOW MUCH CARBON DO YOU NEED?
Most masts have a carbon content that varies between 30% and 100%. This influences the following factors:
- Price. Carbon fibre is an expensive material. The higher the carbon content, the more you have to pay for a mast.
- Weight. Higher carbon content means less weight. And if you have less weight to move around, that means your sail is easier to control.
- Response. The higher the carbon content the more responsive and direct your rig will feel.
- Durability. The downside of carbon fibre is that it is quite vulnerable on impact. So if you have a 100% mast, you should be extra careful not to drop it on the street or smash it on rocks. This will cause tiny cracks in the material that lead to weak points in your mast.
Fundamentally, a mast is made from two material types: fibres that give the strength and stiffness, and the resin that keeps the fibres together.
The most used resin is epoxy; and most manufacturers use a mix of carbon and glass fibres. The carbon content is defined as the ratio between carbon and glass fibres. The epoxy is not taken into account. So '100% carbon' means that the mast consists of only carbon fibre and epoxy, and contains no glass fibre.
Assuming similar bend characteristics, sails will always perform better on higher carbon percentage models. But for durability - especially for wave windsurfers - 80% can be a good mix for durability and performance.
The Bend Curve represents the shape of your mast under load. As we normally use conical-shaped masts (wider at bottom than top) the mast top bends a lot more than the bottom under load.
So the Bend Curve describes the difference in deformation between the top and bottom part of your mast. Below image gives a (exaggerated) view of the difference between Flex Top, Constant Curve and Hard Top masts.
A Flex Top (aka Soft Top) mast has a relatively stiff base and a flexible top. A Hard Top mast has a relatively flexible base and a stiff top. The total stiffness (IMCS value) for a given mast length is typically independant of flex type.
The IMCS value indicates how much your mast bends under load. A lower IMCS indicates a more flexible, or 'softer' mast.
Most mast manufacturers adhere to the more or less normalized stiffness for each mast length. E.g., 400 masts are often made at 19 IMCS, 430s at 21, 460s at 25 and 490s at 29. Hence longer masts are mostly stiffer than shorter masts. Unifiber also follows the above IMCS values per given mast length.
Since almost all manufacturers use the same IMCS values, you don't really have to pay much attention to it. But you could use this knowledge to your advantage:
INFLUENCE OF WINDSURF MAST STIFFNESS ON SAIL BEHAVIOUR
Mast Stiffness Higher than Specified By Manufacturer
- More stable sail
- More power
- Fuller profile
- Better for heavier riders
- Good for flat water sailing
Mast Stiffness Lower than Specified By Manufacturer
- Less stable sail
- Less power
- Flatter profile
- Softer feeling
- Better for lighter riders
- Adds control and speed when sailing choppy water
Changing the stiffness and or Bend Curve of masts is possible in a number of ways. For example, by extending the top or bottom of the mast; or even cutting the mast.
Also, sometimes, mixing different bases and tops is possible, often with considerable influence on both the Bend Curve and IMCS. But this isn't necessarily possible on all brands, and is not intentionally possible or recommended with Unifiber masts.
Out of these possibilities, we'll highlight this very easy and practical one to soften your rig:
Extend the bottom section part of a shorter mast with 30cm extra extension. For example, a 430 mast with 30cm extension becomes a 460.
The result will be a 460 mast with the stiffness of the 430 mast. The stiffness characteristic will be as per the 430, but slightly stiffer (approximately plus 1 on the IMCS). The Bend Curve will be as per the 430, but slightly more flex-top (around plus 0.5 on Bend Curve).
Understanding the above and knowing your mast will help you to improve your sailing performance and have more fun on the water.
INFLUENCE OF WINDSURF MAST BEND CURVE ON SAIL BEHAVIOUR
- Looser leech
- Less power
- More control
- Centre of Effort moves downwards
- Tighter leech
- More power
- Less control
- Centre of Effort moves higher
Not enough theory for you? Well, read on and we’ll tell you how we test various sail brands’ masts with our own specially-built machine.
HOW MAST BEND CURVE AND IMCS ARE CALCULATED
The Bend Curve (BC) and IMCS stiffness can be determined via the commonly used IMCS mast measurement method.
This is calculated by hanging a 30kg dead weight at the mast’s midpoint and measuring the mast deflection at 1/4, 1/2 and 3/4 of its length.
Let's call the deflection at 1/2 the total deflection.
Now, calculate the top section (3/4 length) deflection as a percentage of the total deflection, and also the bottom section (1/4 length) deflection as a percentage of total deflection. Subtract the top section result from the bottom section result and you get the Bend Curve figure.
Most masts are between 6 - for a very low bending (stiff) top, and 20 - for a very high bending (flexible) top.
Stiffness will be determined through midpoint deflection, by a standard formula.
It should be noted that particular sail manufacturers may use alternative or proprietary Bend Curve measurement methods.
The Unifiber mast selector, below, provides information on masts offered by sail brands. To enable easier comparison masts are categorized as Hard Top, Constant curve or Flex top.
WINDSURF MAST STIFFNESS MEASUREMENT
See below for the calculation method and a few typical mid-deflection figures (30kg load).
IMCS stiffness = ( length x length x length ) / (460 x 460 x mid-deflection )
For the ‘length’ we normally use standard lengths (e.g., 400, 430, 460...). Length and mid-deflection are measured in centimetres. Mid-deflection is with a 30kg load.
|Mast length||IMCS||Mid-deflection (mm)|
Adhering to this accepted measurement method enables easy transfer of results and comparisons with other tests. Our measurement set-up enables a measurement resolution of +/- 0,1 IMCS points and about +/- 0,25 Bend Curve points.
Absolute measurement accuracy is very hard to determine because no reference mast can be obtained. In the event that you are interested in details of above measuring method, or in building your own measuring set up, please contact Unifiber.
Unifiber started a few years ago to measure and collect mast data from practically all known mast / sail manufacturers.
To enable a reliable outcome we measured a number of masts of the same type and length. We learned that production tolerances are seldom below 1 BC and/or IMCS point.
Notwithstanding these production tolerances, we've seen an overall trend from hard-top masts towards constant curve masts for some race sails.
We started testing masts in 2011. Check our latest Masts Selector, where you will also be able to click through to previous versions.
WINDSURF MAST DURABILITY
WHY UNIFIBER MASTS
Unifiber masts give unbeatable value for money, performance and durability thanks to a consistent pre-preg manufacturing process, with stronger, integrated ferrules and a high-quality surface finish.
Unifiber offer 99 different choices of carbon content, diameter and 3 different bend curves to match almost any sail.