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// Tushingham SDM Carbon 60%
SDM Carbon 60%
Tushingham is the only sailmaker with sophisticated, in house electronic mast testing equipment. Other sailmakers have to rely on data supplied by the mast producers, which cannot always be relied upon to be accurate.
The SDM C60% is recommended for use in sizes:430; 460cm and 490cm
in all non-racing disciplines:
Following extensive R&D, Tushingham have identified the bend curves that obviously work perfectly with Tushingham sails, but will also improve the performance of many other sails. In a recent Boards Magazine test, many sails from other brands performed better on a Tushingham than on their own recommended mast.
Construction and Quality
Batch testing, in house, ensures all Tushingham masts are built to their exacting specification and quality standard.
A windsurfing mast must have an overall stiffness within the range specified by the sailmaker for any given sail.
Stiffness is measured by supporting the mast at each end and applying a 30kg weight to the middle. The mid-point deflection figure is applied to a formula that takes account of the mast’s length to give an IMCS number (Indexed Mast Check System) The bigger the number the stiffer the mast; IMCS numbers typically range from about 11 (soft junior mast) to 36 (stiff race mast).
Bigger sails need stiffer masts to support the extra forces so it’s normal for longer masts to be built stiffer with higher IMCS numbers.
For the technically minded, the formula for calculating IMCS is:
IMCS = Length(cm)3 / Mid Point Deflection(cm) x 216225
Stiffness does not tell the whole story. The shape of the bend curve is also important; we’ve all heard terms like ‘constant curve’ & ‘flex top’ but what do they mean? In fact, these are quantifiable terms. When we measure the half height deflection for the IMCS test, we also measure deflection at the quarter and three quarter height points. We express these as a percentage of the maximum deflection, for example here are the test results for a ‘constant curve’ 460cm IMCS 25.
Maximum deflection at ½ height = 181mm (which calculates to IMCS 25 on a 460cm length)
Deflection at ¾ height = 138mm which is 76% of maximum deflection 181mm
Deflection at ¼ height = 116mm which is 64% of maximum deflection 181mm
The bottom half of the mast is always stiffer than the top. If we subtract the ¼ height percentage from the ¾ height percentage we get; 76 – 64 = 12. This mast has a bend curve number of 12
The industry standard terms describing windsurfing mast bend curves are:
0-6 = Hard top
7-9 = Hard Top/Constant Curve
10-12 = Constant Curve
13-15 =Constant Curve/Flex top
16-18 = Flex Top
19-21 = Flex Top/Super Flex Top
22+ = Super Flex Top
The higher the number the more flexible the mast is in the upper half relative to the bottom
The mast in our example just falls into the ‘Constant Curve’ range and can be described as a 460/25 Constant Curve with a bend characteristic of 12.
What is best?
How do these different bend characteristics relate to my windsurfing?
We need a basic understanding:
A Constant Curve mast is over 10% softer in the head than in the base, historically it’s what the industry considers a middle of the road shape for all round windsurfing. Our testing indicates that a slightly softer head will improve the feel of most sails. We consider a bend characteristic of about 15 (Constant Curve-Flex Top) to be optimum for most freeride and slalom applications.
The advantage of a slightly stiffer bottom/softer head set-up is that it locks the power in at the bottom of the sail whilst allowing the upper part of the sail to react and breathe with variations in wind and chop. This characteristic becomes more important as sail size increases and the sail becomes harder to handle. We therefore, move towards a slightly more flexible top as the mast length and sail size increase.
The requirements for a wave or freestyle sails are slightly different. These sails are in any case smaller but they also benefit from a more ‘lively’ feel. This requires a mast that’s relatively softer in the middle and lower section which means a lower bend characteristic, a number in the range 13 to 14. The rig will feel more powerful when you sheet in but will not be as stable when overpowered.
RDM or Standard Diameter?br/>
We are building our RDM’s with softer bottoms because this delivers the best performance in wave and freestyle sails where the durability of the RDM is a distinct advantage.
If we consider a crossover sail such as the Storm we can change its character with mast selection. The RDM will deliver a more ‘springy’ wave style feel, whilst the SDM with its stiffer bottom and more flexible top will promote a more locked in slalom style feel. Those windsurfers who blast back and forth across a windy lake may feel more comfortable with the SDM, whilst the RDM may be the preferred choice for freestyle or chop hopping at the coast. Of course, these are not hard and fast rules; personal preference is a significant factor.
Selecting the right Tushingham mast
“A sail is only as good as the mast it’s rigged on”
There is a Tushingham mast to suit all pockets and performance aspirations.
Which mast should I choose?
Obviously the mast must fall within the IMCS compatible range quoted for the sail and be of appropriate length. Readers of this website should also have a good idea of bend characteristics and be able to make an informed decision about what will suit their style of sailing. A few pointers:
Weight – A light mast will feel lighter, which is obviously good, but most importantly a light mast will react faster (reflex response) and have a more lively feel. This faster reflex response allows the sail to breathe and exhaust correctly for best performance and a more comfortable ride. The advantages of a faster reflex response are felt in planning conditions, powered up, particularly over choppy water.
Light weight is achieved through a high carbon content which naturally comes at a price.
Carbon % – Higher carbon content means less weight for a given stiffness. For example a 460cm 25 IMCS Carbon 45% should bend to exactly the same curve and stiffness as 460cm 25 IMCS Carbon 100%. When the sail is rigged in a static situation it should look exactly the same on either mast. The difference will be felt on the water as the dynamics of light weight and faster reflex response come into play. There is a very big difference in feel from a 45% to a 75% and on to the ultimate 100% carbon construction.
The best mast for any windsurfer, expert or novice, is the 100% Carbon item. Choose the best you can afford, but temper this with considerations connected with the likely end use, particularly durability. Furthermore, consider where best to spend your money as a part of an overall quiver. For example; a light mast will make far more difference in a bigger sail where the overall weight is a key issue.
Standard diameter (SDM) or reduced diameter (RDM)?
RDM – Advantages:
Thinner in the hands, many prefer this feel in transitions where the mast is held.
Thicker wall, more durable
Relatively softer in the middle for a springy feel
More suited to wave & freestyle applications
SDM – Advantages:
Lighter for a given stiffness
Range of top section stiffness available for speed/slalom applications
First choice for camber induced sails
More locked in feel with better top end performance
More suited to freeride, slalom, racing and speed applications.
Floats better for easier water starting
Generally speaking it’s obvious that the SDM is the natural choice for larger sails, for speed, slalom, and light/medium wind freeride. Conversely, the RDM is popular with wave and freestyle sailors.
The choice of mast for a high wind freeride sail like the Storm is interesting because it will work on both types of mast. A Storm rigged on an SDM will have a locked in slalom feel, even more so if the mast has a high carbon content and light top section. This would suit a more speed oriented sailor or one looking for comfortable effortless straight line performance blasting back and forth across choppy water.
The same sail rigged on an RDM will have a springy feel and may be preferred by the more manoeuvre orientated sailor, it will have less top end stability but a softer feel. It comes down to personal choice, a choice that can only be made if the user has a reasonable understanding of how a mast works.
The Need for Speed!
Speed enthusiasts should be aware of the importance of the bend curve numbers. There is more information on the bend curve page but speed sailors operate in extreme overpowered conditions where only a stiffer lower section and flexible top mast will deliver the speed and control. Look for bend curve numbers in the high teens.