Mast Article in Boards mag Copied from the forum.

As Gaastra was the feature in the said article I wanted to copy this post in order to sum up some my feelings on the article and to add a couple of things.
1) Gaastra and Dan Kasseler built the sails on the Gaastra Masts to rig and feel how they do on those masts based on feedback from their test team. In reality it is true the Gaastra's rig a little flater than what Boards testers would like or are used to, but it is the way they are.
2) It is very difficult to get two different carbon content masts with different reinforcing to have exactly the same bend and Gaastra has optimised the sails to set on both 100 and 75 RDM bend curves and there is a slight diference.
3) Outhaul setting is something that is really subjective and is really part of tuning for rider, weight, windspeed and angle and water state. Flat for overpowered and flat conditions mabe a bit let off for choppyer water where more grunt is necessary etc etc.
Rig, tune, compare, rig again, swap with your mate and compare and rig again.

We have done this on Maui with identical rigs in different masts and came out with very different results from each rider.
Read below a good explanation of why!!


This deserves a separate thread. I read the mast article in Boards and well done to them for trying to look in depth at a complicated issue – and one which of course picks up on stuff often mentioned here on the Forum before. Namely, that not all masts are the same. Three cheers to Boards too, for actually trying to measure mast bends and in attempting to assess what difference changing masts can make to a sail. The results they found were; 1) That the mast's IMCS stiffness rating was not always as labeled. (The differences are not astounding, and are on a par with different board weights from the same brand and model.) 2) That mast curves can vary within this IMCS stiffness, thus altering the shape and performance of a sail. Curiously, this means that you can sometimes make a sail perform better by not using the sail manufacturer's own mast brand. (If only we knew which one to pick instead). 3) That some cheaper masts are actually better performers than more expensive ones. (Shock horror! No. You're kidding me? Really? So the most expensive brand isn't always the best? I may have to lie down...) 4) That RDMs often offered a different performance than SDM masts – and that they, the test team on one beach in a sunny place with constant winds, usually preferred the RDMs, often against the recommendations of the sail designer. All that is fair enough. The Forum sail-makers like Matthew and Bigfish have been going on about many of these issues for some time and it has certainly been said here that IMCS stiffness is not to be relied upon – perhaps just like the 'measured' volume figure we are quoted by manufacturers for our boards. However, I don't think we need call in the Office of Fair Trading over this and some perspective is needed before we all go off and change our kit. I've now read the Boards article twice and think it's a bit flawed. On one level you could sum up the article by saying: "You can sometimes improve the performance of your sail by changing masts". Which, though true, is well down the list of advice that gets you windsurfing. Higher on that list, we might say: If you are not planing then rig a bigger sail or pick a floatier board. If you want more time on the water, then move to the coast. Book more holidays. When over-powered, try more downhaul/outhaul. And so on. So this is potentially a very nerdy article about sail tuning which is more likely to confuse people, rather than inform. You can really get bogged down by the idea that if you set one sail on one mast with X amount of downhaul the boom length is Y whereas if you use the same amount of downhaul on another mast the boom length is Z. Perhaps one bigger criticism is that the article doesn't really explain why this happens. So for the nerds like me, the following paragraphs should clear many issues up and a similar explanation really should have been at the head of the Boards article: Let's start at the beginning with some basics. A sail is rigged on a mast to give it a solid leading edge, and we use downhaul and outhaul to set the sail panels crinkle-free, in the preferred shape of a 'sail' or wind-harnessing aerofoil. The mast can bend both fore and aft, and sideways, and the bend characteristics of any mast can be used to control the power and performance of the sail. This gets a bit complicated here. Traditionally some say that you want the mast tip to bend to leeward to spill wind when a gust hits. In reality the leach is freed when the sail twists open and this twist is achieved by a combination of sideways and fore and aft mast bend which flattens cloth at the front of the sail – which in turn allows the leech to fall away and sheet out. Because the leach at the head sheets out independently of the lower half of the sail you keep forwards drive from low down in the rig whilst spilling excess power at the top two battens. The mast bend can happen reactively to spill wind as a gust hits. Or else we can depower the sail more from the start, by bending the mast more with downhaul tensions set on the beach. In fact we use both downhaul and outhaul to control the power delivered by a sail, and this process of tweaking is called tuning. Any rotational sail is designed with a luff round or curve cut into the sail to deliberately mis-match with mast bend, so that you get a bit of rotation at boom level and no rotation at the head. Put crudely, there's more luff curve at the boom area in relation to mast bend and this spare cloth creates rotation. At the head, the sail luff matches the mast bend exactly so there is no rotation there. This again gets complicated because some of the spare cloth is made up from the sail's luff tube. Where the mast diameter is small, there is more spare luff tube cloth. So changing from a SDM to a RDM means you have effectively changed the luff round of the sail because each mast type has different mast diameters at various heights on the sail. In theory, there is now more luff round at the boom area with a RDM because this is where the reduction in diameter is most noticeable. This is turn would imply more sail rotation here – whereas in practice it does not, simply because chosen downhaul and outhaul settings will be different plus many RDM masts bend more in the middle. There's a bit more explaining to do here: All masts bend under load but mast curves vary from constant curves, to those which are bendier at the head. If a mast bends more at the head this should mean a flatter sail there. In theory too, a mast which is bendier overall (like the ones tested for IMCS which don't turn out to be as stiff as their IMCS labels would claim) will set your sail much flatter with a given downhaul tension – this in turn will mean you have to extend the boom (set it longer) to get any outhaul tension. The Boards article goes on a lot about how different masts gave the same sail different neutral outhaul settings. They went on to make performance judgements on this basis, But it doesn't quite work like that. We set sails with downhaul tension and outhaul tension and these forces apply panel tension to the sail cloth which give the sail stability. The downhaul tension is also the primary cause of mast bend, being a vertical compressional force from mast tip to mast foot. But the downhaul tension is applied to the mast via the sail cloth and this means that in turn the cut of the sail can actually influence which part of the mast bends first, almost regardless of tested mast curve and mast stiffness. (True) Where the Boards test fell down was in that they made no mention of how mast extensions lengths were varied with the same 430 masts and they made no attempt to actually measure downhaul loads. You can take two masts of the same length and same IMCS but when rigging them inside the same sail you will find that the extension needed varies to set the sail appropriately or to achieve its optimum performance. In simple terms, if the mast is softer or bendier then you need a notch more extension to apply the same amount of downhaul tension as when rigging the same sail on a stiffer mast. The sail then sets flat and in turn you need a longer boom to get any outhaul tension. The opposite case is where you use a stiffer mast on the same sail – here you have to apply shed-loads of downhaul to get the mast bend where the sail sets adequately and half a centimetre less mast extension might be the norm. Sometimes it's not about how much extension so much as how hard can you pull to get it on. With a stiffer, less-bent mast, the sail will invariably be more rotated at the boom and this in turn means that the neutral setting for the boom will be where the boom is set shorter. But before you get over excited about all that wealth of nerdy information you could file the whole lot under 'tuning'. Three sentences then suffice. Bendier masts need less downhaul and are suited more for lightweights who load up the sail at lower windstrengths. Whereas heavier people might benefit from stiffer masts. In either case, tuning is everything. Boards test team however came up with remarkable conclusions such as: "This sail was undoubtedly faster on this mast." This made no distinction about the weight of the sailor, the mast length with extension used, or the boom length setting. It assumed that there was only one setting for the sail – namely the one they thought was right, when pulling on the downhaul on the beach. Sadly there is not much credible science going on here. Sail tuning is not like that. It's a trial and error thing where one sailor narrows down the variables to suit his stance and style and body weight and kit. To improve your personal board speed you need to test yourself against a regular sailing partner or else against the GPS. Then you need to take the same winning kit and the also-rans to a different sailing spot with different wind and water conditions – whee you will often find that different sails and kit combinations work better. Then and only then can you draw some conclusions. Sadly, a different sailor – especially a heavier or lighter one – would draw different conclusions again. But, overall, for the average, recreational sailor, this is one of those articles that'll really f**k you off or, at best, confuse you. In reality, when choosing a mast the song remains the same. When buying a mast to match your sails, choose from those which are the right length and IMCS stiffness first. Then choose the highest carbon content mast you can afford. Then cross check the weight of the mast you think you want against other brand's rivals in the same group. Then go for the lighter one if you can afford it. If you've already got a mast at home – then check to see if that fits before splashing out on anything new. There are usually enough tuning options via the downhaul and outhaul to make a modern sail set adequately on almost any mast.