Quick question. Why do sail making companies often design sails with a luff of, lets say 429cms and then recommend a 400cm mast? All that does is result in you needing to use a long extension (I don't like doing this in waves with an RDM).
So, why can't they design the sail with a luff 1cm longer and take into account that it'll be rigged on a stiffer mast?
Or is it simply a way of selling more masts?!
It is more to do with the stiffness of the mast.. It is not always obvious, but the wrong stiffness mast can kill a sails performance and wind range.
Some masts allow you to mix and match so with a luff length of 429 you can make a mast of 415 (400 bottom, 430 top).
I do this with my 5.2, it works well 
I agree with Nebbs that mix n match is good, but I do wonder that it leaves too many tuning options - with his 5.2 Ezzy he could choose 400 + lots extension, 415 (with mixed bits) or his 430 with more extension. Any would work well and only one will be spot on for his sailing style, weight, etc.
Too hard to decide what may work best.
I agree that the current situation is weird as if a 5.2 has 429 luff why not just design it for a 430/21? Maybe they are trying to maximise the number of sails you can get on one mast but it would appear not as
(1) they want to sell more masts!
(2) at the other end of the spectrum there are a lot of 4.0 - 4.2 that could be designed to fit on a 400 but they deliberately cut them on a 370. I think that kinda rules out that they are deliberately trying to get a 5.2 on a 400 to help us all out
Be really interested to hear from a sail designer....
the sail is softer by using a smaller mast - usually preferable for the average weight sailor.
your overall rig is lighter by using a smaller mast.
the swing weight is less for doing loops etc. that is why a lot of companies are making more compact sails. i would never use a sail now where a 4.7 doesnt rig on a 370 for that reason.
The most extension my Koncepts have is 120mm, 5.0 to 7.5 so some designers are working to a mast length
Maybe designers want to reach better performance in e.g. waves (where lower part of the sail has less power), by catching more wind in the upper sail area, that's why longer luff, but the sail prefers softer feel and that's why shorter mast is required...
sometimes it is nice to have choice. My 5.2 has a 428 luff and recommended mast is a 400. But as a heavy guy i preferred it on the 430. When I lost weight and/or if it is going to be really gusty I like it on the 400
Sail designers have a particular sail shape in mind, for a given model and they often design/test a specific size and mast type.
In the modern era, they translate the design onto a computer or old-school style using templates. To make different sizes, they then just resize the templates, usually by about 10% or so - which then usually suits the next mast size too.
So simply speaking, the designers often arn't thinking about mast lengths specifically... Some sail designers do consider mast lengths -> the 2008 KA Koncepts had luff lengths that were attempting to match mast lengths... they were lengthened the following year.
I actually was a sail designer, not for windsurfing but yachts and I can tell you that a 400cm mast with a 30cm extension is not the same as a 430cm mast. It's all about twist profile and even though they look the same, the sail will set up differently on each mast. You can use these differences to tune the sail for different weight ranges but after using the wrong mast in race sails I can definitely vouch for the differences. You have to trust that the guys designing the sails actually know what they are doing and it's not just a matter of hitting the scale button on the computer...
I think everyone here is missing the point.
Like Jethrow - we know that a 400 +30cm extension is not the same as a 430. The point is that a sail with a 430 luff can be designed to work on a 400 + 30cm ext, or designed to work on a 430.
If you make a range of sails and the 4.2, 4.5 and 4.7 all fit on a 400, and the 5.2 has a luff of 429cm why not just make the 5.2 sail to suit a 430 (stiffer) mast? They already have to make other sails in that range set well a 430, like the 5.5 and 5.7 for example.
Why have all the sails in one range use between zero and 15cm ish of extension but have one size sail need 29cm of extension?
I think this is pertinent as wavesailors tradionally don't have long extensions - most go to 25cm ish - so to need a 30cm extension means buying another one.
I can understand the 6.2 kinda size needing lots of extension as some wavesailors want to have one big big sail for grovelling and you'd not want to have to buy a whole mast for that one sail. But considering just about all of us have a 400 and 430 masts, and 4-5 sails, why make the middle size need a sh!teload of extension when it is easy to have it designed so it works on a 430 with no extension?
^^^ Gaz I think it would be more than that.... but all the little bits add up.
Lets not get off track - My point was that they can choose to make a sail set well on different masts but they all seem to choose to make a sail with 428 - 429 luff set on a 400 and crashlanding and I ask why?
Barn if your biggest sail is a 5.2 or 5.4 and all your sails are on a 400 you are a lucky fella
I have 4.0 - 6.2 for wavesailing and even if I was a bit lighter I reckon it would be the same
S like it or not, I have to have 2 masts.
If the 5.2 was cut for a 430 I'd only need one extension but as it is currently I really need 2 extensions
