Select to expand quoteHomestraight said..
Why do neil pryde have flex top masts when most others are constant or hard. Does neil pryde handle gusts better with flex tops?
I've seen a nice Maui sail but that means buying at least a constant curve mast. I've already got boom, base and uxt extension by NP just not mast and sail.
As a newbie buying first gear it's ridiculous detail to work through...
Help appreciated... Noting I already know neil pryde and maui/severe/gastra generally don't match... Have seen the table.
Here's a bit of information overload for you.
I copied it from a website a few years back.
The author (A Scandinavian Formula sailor) did a lot of mast testing and appeared to have a bee in his bonnet about incorrect info from manufacturers.
In particular he mentions Maui Sails and it appears he was correct.
Maui have just recently announced their new mast line and the change is to 'Constant Curve'. Suggests the previous Maui masts were not.
Personally, I've measured many Maui masts (my sails since 2005) and they are always 'hard top'.
Nevertheless, a lot of good insights here........
Stiffness.
Measuring how much the mast deflects related to the length, you have a figure for the stiffness of the mast. When a mast is imprinted with say IMCS 32, it is the stiffness that are referred to. The bigger the number, the more the stiffness.
Bend Curve.
If you measure how much the mast deflects at the 1/4 point of the mast, at the midpoint, and at the 3/4 point you get some figures telling of the way the mast are bending under load (called bend curve or bend characteristics). If we for instance say that a mast deflects 13 cm at the 1/4 point, 20 cm at the midpoint, and 15 cm at the 3/4 point, you find your calculator and do as follows:
First you calculate how much the mast deflects at the 1/4 point in % from the deflection at the midpoint. In our example it's (13 x 100 / 20) = 65 %.
Next you do the same calculation for the 3/4 point - that is the deflection of the mast at the 3/4 point in % from the deflection at the midpoint. The calculation is (15 x 100 / 20) = 75 %.
Now all you have to do, is to subtract the two figures - that's 75 % minus 65 % = 10. To be correct, the denomination is not 10 % but 10 %-points. Anyway, you say that the mast has the bend curve of 10 *).
To make it easier to understand the bend curve figure you can translate the figures to these IMCS terms:
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 misleading use of bend curve characteristics of (some of) the companies.
It is evident from the scale that "Constant Curve" doesn't mean that the mast is equally soft (or stiff) from the bottom to the tip. Constant Curve means that if you hang a weight of 30 kg from the midpoint, the mast deflects 10 - 12 %-points more at the 3/4 point than at the 1/4 point. No more - no less. You can't say that a mast is "relatively Constant Curve" - as heard from a well known sail designer in an excuse of his top stiff masts.
In spite of this lack of room for mistakes, almost all masts from the companies are called Constant Curve - wether they are or not **). Perhaps this is so, because there is most sale in telling that the masts follow a middle course. The underlying message of the companies is that the mast has a standard bend curve, so that it fits all modern sails. But often it is misleading *), and the buying of a mast according to the inaccurate or perhaps immoral playing with names that - as we saw above - is in fact precisely defined, has cost many a windsurfer lots of money for no good.
For instance, Gaastra, Fiberspar (the longer masts) and Maui Sails masts are all very stiff in the tops (most often placed between 5 and 9). These masts are specifically made for the companies own Vapor (former Nitro and Neutron) and TR sails. The masts are not Constant Curve - in spite of the pretence - and they mostly only fit to the sails mentioned ***).
A couple of years ago Neil Pryde had a pretty sofisticated way of spreading fogs: They published some "Bend Offsets", which (when you calculated on the figures) placed the masts in the middle of the Constant Curve scope. The figures obviously more reflected a kind of "calculating backwards" to get the wanted results, than they reflected genuine measurements. A more recent Neil Pryde trick is to indicate approval to the IMCS system by telling the IMCS stiffness (say IMCS 21), whereupon they - without any defintion at all - name the bend curve "Progressive Flex". Are you confused? No need to be - just remember that the Neil Pryde masts are pretty soft on the tops (most often placed between 14 and 17 ****)), and that they are specifically made for Neil Prydes own sails. The masts are not Constant Curve, and you can't use them in many sails from other brands.
What's most important - stiffness or bend curve?
What to look for - stiffness or bend curve? Unfortunately we get no help from the companies that (besides their empty way of using the phrase "Constant Curve") only inform us about the stiffness of their masts (say IMCS 32). And - as we saw - the stiffness is far from the whole truth about the masts. In fact you could pretty easily argue that information about the bend curve might be more important. Since the stiffness tells something about when the mast starts working (at what load), the bend curve tells something about how the mast shall work when loaded.
How does the soft and the stiff areas of the mast influence the appearence of the sail?
Working in the sail, the mast of course deflects the most in the softest areas of the mast - and deflects least in the stiff areas. Where the mast deflects the most, it pulls away from the leech - in this way straightening the sail (with little depth) on level with the soft area. If the sail has a camber inducer at this place, it often rotates easily - or perhaps it is even not pressing properly on the mast.
Conversely, the stiff areas of the mast shall not move a long way from the leech - thereby not straightening out the sail-cloth on level with this stiff area (creating lots of depth). If the sail has a camber inducer at this place, it most often presses hard on the mast - often to a level at which it's difficult to rotate. And when it rotates, it is often accompanied by a loud "camber-bang."
The same sail rigged with a Flex Top and a Hard Top mast respectively.
If we think of rigging the same sail with the two mast-extremes respectively (for instance a Neil Pryde mast with soft top and a Maui Sails mast with stiff top), we shall try to predict the differences. It's important to note that this is not science - just a kind of common "knowledge" among the gang of old windsurfers from the local beach:
With the Neil Pryde mast the sail shall have a big depth (much profile) in the bottom and in the middle of the sail, while the top of the sail shall be pretty loose. Often the change from the area with big depth to the loose area shall be very "sudden" with a lot of wringles. The center of effort shall probably be placed forward (and deep) in the sail, and the camber inducers shall have a lot of pressure. Actually it could be necessary to remove a couple of spacers - or to file off some of the plastics - to make them rotate. As the mast is pretty stiff in the middle sections, a lot of downhaul is probably needed.
With its loose top the low-end pull from the sail comes from the deep profile in the bottom and the middle sections. And often the angle of incidence around the mast pocket shall be pretty rounded, so that the air flow over the sail shall be very attached and make it easy and steady to sail.
With the Maui Sails mast the sail shall appear pretty flat (little profile) in the bottom and middle sections, and the top shall not be very loose. The change from the flat bottom to the not-especially-loose top is spread over a large area, and the sail shall have a rather harmonic appearence - gradually twisting towards to the top.
The center of effort shall probably lie a way back, and the camber inducers most often shall not press very hard on the mast - in fact sometimes you shall have to place some spacers between the battens and the inducers. As the mast is relatively soft in the middle, you shall probably not use a lot of strength to downhaul the sail - and using too much downhaul force might almost collaps the sail in the middle.
With the flat bottom and middle sections of the sail, the low-end pull are caused from the relatively tight leech high up the sail - and from the fact that the center of effort is placed a way back.
Often there's a tendency that the angle of incidence around the mast pocket shall be rather "sharp" (the sail is almost cutting its way through the air), and in this way it is pretty easy to over-sheet the sail. As the air flow over the sail is always at risk of being turbular, it is easy for the sail to loose its power. A sail with a sharp angle of incidence might be exellent for very good sailers, but for us mortals it might be a little nervous.
Some findings when measuring masts.
Here is a link to some measurings of masts. Even if the measurings shown are selected, the figures are still mostly raw data - but here under you'll find some of the simliplified and generalized conclusions, you can make from the material:
*
The mast neither changes stiffness nor bend curve, as the temperature changes. Even though you by means of the IMCS test can't find any difference, if it is 0 degrees celsius or 25 degrees celsius, of course you might speculate, if the mast perhaps gets a little "slower" in the lower temperatures - that is if the "flex response" is dampened.
*
If you shorten the mast (from the bottom!), it gets softer and doesn't change its bend curve. Of course it's not wise to cut off so much that the mast foot/extension doesn't fit the mast - or that the boom is fixed above the extra strong boom area. And as indicated - never shorten the mast from the top.
*
If you extend the mast it gets stiffer (most with Flex Top, a little less with Constant Curve and least with Hard Top masts), and it almost doesn't change bend curve. Of course you shall not extend the mast so much that you clamp on the boom below the strengthened area.
When you try to find a way to calculate, what approximately happens to a mast that you extend, you'll have to decide what you'll understand with "extending". For instance, how long extension are we talking about (in numbers or relatively)? How much extension in the mast are we talking about (in numbers or relatively)? What is the stiffness of the mast to extend? What is the bend curve of the mast to extend? And so on and so forth ...
If we make a fast decision and say that we are talking about a 30 cm extension of the mast by means of a 50 cm extension device (that's of course 20 cm up in the mast), then - based on numerous measurements - you can (very) roughly say that ...:
*
All masts keep (approx.) their bend curves when they are extended.
*
All masts become a little stiffer (according to the IMCS standard) when they are extended.
*
Hard Top masts become relatively least stiffer (around 2-3%).
*
Flex Top masts become relatively most stiffer (around 6-7%).
*
Constant Curve masts become stiffened up between Hard Top and Flex Top masts (around 3-6%).
This can roughly be "translated" in this way ...:
*
If you extend a Hard Top mast with 30 cm, so that it reaches the length of the next mast in the line, the extended mast is supplied with 1/6 - 1/4 of the extra stiffness necessary to get on level with the next mast in line.
*
If you extend a Constant Curve mast with 30 cm, so that it reaches the length of the next mast in the line, the extended mast is supplied with 1/4 - 1/2 of the extra stiffness necessary to get on level with the next mast in the line.
*
If you extend a Flex Top mast with 30 cm, so that it reaches the length of the next mast in the line, the extended mast is supplied with 1/2 - 3/4 of the extra stiffness necessary to get on level with the next mast in the line.
The more mast with or without extension that are measured, the more precise the ability to predict what happens as to change in stiffness - and the less likely it is that mentioned general rules have to be changed.
*
If your mast has become "excentric", this doesn't change the bend curve significantly. However, as the mast now is a little "pre-bend", it equals it has grown a little softer.
There is a tendency that the increasing softness that follow heavily use, are most noticeable in the areas that work the most - that is the top of the mast. But - you have to use the mast very much, before you face any problems in this respect.
In short, paring mast with sail (race sail/race mast).
*
If you use the mast the sail producer recommends, you don't risk anything.
*
Never use a Neil Pryde mast with a Gaastra or Maui Sails sail.
*
Never use a Gaastra, a Fiberspar (the longer masts) or a Maui Sails mast with a Neil Pryde sail.
*
Think about it, before you use any of the obove mentioned ("extreme") masts with other sail brands (North, Severne, Gun, Naish, Sailworks, Aerotech etc).
*
If you choose a "detuned" Gaastra or a Maui Sails mast (for instance the Maui Sails SRS 75 % mast), there is a tendency that these masts fit in the Constant Curve scope. The same is true for the older and longer Neil Pryde Freeride Pro masts.
*
A lot of 100% carbon masts are manufactured in two Italian plants. Even if the sail producers say that they order their masts from their own specifications, it is a well known "secret" that you might be lucky enough to buy a a cheap mast (for instance a GUN Dominator) with IMCS numbers that is hardly distinguishable from the numbers associated with one of the much more expensive masts from one of the well reputed (and expensive) sail producers (Neil Pryde for instance). Of course this is just an example!
Footnotes.
*) There is a little further information to get in the calculation for bend curve than just the figure ("10" in the example). If you compare the 1/4-deflection and the 3/4-deflection mentioned (65% and 75 %) with for instance deflections of 63% and 73 %, you'll end up with the same bend curve figure. However, intuitively you might see that the 65/75 mast is a little more "U-shaped" than the 63/73 mast, that is a bit more "V-shaped." Admitted, this is perhaps a little nerded.
**) There are exceptions - Sailworks seems to be honest about their masts.
***) The new sail designer for Gaastra (Dan Kasseler) came from Naish Sails, where he designed sails around some (probably) traditional Constant Curve masts. At Gaastra he inherited the top stiff masts from Barry Spanier and Phil McGain, and he has built the new Gaastra race sails (the Vapors) around these masts. Kasseler says that he'll continue to design sails around those original Gaastra (former "Ignition") masts - but let's see ... At Naish Sails he had a great success building sails around traditional masts - for instance the sail that helped Finian Maynard making his World speed record in the autum of 2004.
In an all new video at the Maui Sails homepage, Phil McGain one more time tells us that his SRS 100% masts are Constant Curve. But the truth of this statement doesn't grow with the reiterations of the falsity. Maui Sails race masts are and have always been Hard Top - Constant Curve!
****) The bend curve of the longest (and seldom used) Neil Pryde race mast (the X9 580) is placed around 12.
Select to expand quoteNotWal said..sailquik said..
Testing the bend curve is and integral part of IMCS testing.
No it isn't. To calculate IMCS you just need a simple deflection measurement.
The calculation of curve requires 2 more measurements which you wouldn't bother with if you were just measuring IMCS.
Do you know if Boards measured curves or are you just assuming that was part of the IMCS measurement?
yes it is... you measure deflection at 3 points: www.peterman.dk/mast-imcs-formulas.htm
Select to expand quoteNotWal said..Sailhack said..
What do AD (sailquik) and kato know about sail/mast technology anyways eh NotWal? 
What I'd give for some of that knowledge (or tow). 
I don't know. I can only go by what they say. 
Pardon my smart @rsed comment NotWal...I blame a mate that brought a bottle of Woodman Reserve around to my place last night.
Select to expand quotemathew said..NotWal said..sailquik said..
Testing the bend curve is and integral part of IMCS testing.
No it isn't. To calculate IMCS you just need a simple deflection measurement.
The calculation of curve requires 2 more measurements which you wouldn't bother with if you were just measuring IMCS.
Do you know if Boards measured curves or are you just assuming that was part of the IMCS measurement?
yes it is... you measure deflection at 3 points: www.peterman.dk/mast-imcs-formulas.htm
Yes I'm familiar with the procedure. The fact is you don't need to measure curve to measure IMCS. They are just 2 things that are conveniently done together.
I think we understand each other now.
Select to expand quoteTe Hau said..
Here's a bit of information overload for you...................
Great find and contribution Te Hau! 
That pretty much confirms and agrees with all my own experiments and observations, but adds more in the area of large sails and the longest masts.
For those who have access to a collection of older Boards (UK) Magazines, the article I referred to in a previous post was in the May 2007 issue.
There are a few minor things the Boards team concluded that I might take issue with, but they deserve the highest respect for taking an excellent, in depth look at what is an extremely neglected area in the Windsurfing Media and doing a very good job of it.
They even attempted to measure the concept of 'Reflex Response' as touted by some masts companies. They came up with what appears to be a logical test but said although the difference between masts seemed able to be seen, they could not measure it to any significant degree.
I wonder if this topic (masts and their part in rig design) deserves it's own thread where we can continue the discussion and add relevant info as it has diverged a long way from the OP's intended question?
Let's get back to basics..... more sideways bend of a mast the more gust response is achieved.
This is achieved by several ways:
Downhaul tension, more downhaul and the mast will, when loaded dynamically induce more sideways bend, opening up leech etc.
Where the mast yeilds first has to match the sail, what is cut in seam shape and luff curve of the sail.
The sail design for the twist is built into the sail.
The flex tip designed rig uses less of the sail to bend the mast sideways and is sensitive to downhaul to achieve it.
The stiff top rig uses more of the sail to bend the mast sideways.
The two more extreme ends of the spectrum work to achieve similar results and is a compromise on other factors of power control, leverage from the sailor, what the design concept is with regards to wind range, feel of the sail etc.
I use the NP set up as I have the masts and unlikely to change as it would mean replacing masts for different sail manufacturers. This is an economical delema mainly. I would say that the flex top is more sensitive to downhaul tension and should be rigged for conditions and the amount to change can seem to be very little,5-10mm and the sail performs very differently. The hard top rigs are less sensitive to downhaul as they rely on more of the sail to promote sideways bend.
I think one of the biggest factors contributing to gust response is overlooked by many.... fin tip deflection and fin twist is just as important as the rig gust response. A very stiff fin will not respond as good as a fin that twist and deflects sideways just the same as the rig but operating in a more dense and thicker medium.
Subtle differences in both the rig and fin setup to match the conditions is the key factors here. This has to match the rider weight and leverage.
I am a relatively lightweight and change to a softer fin (same size) if getting overpowered and extend the range of the sail by a fair bit before I change sails. This works very well and should not be underestimated.
My background is designing and building 18ft skiff rigs, sailing them etc Windsurfing since it was invented and the first ones coming into the country, also an Olympic sailing coach by profession.
So summing up, put the right mast in the right sail so it matches. Pay attention to the way the sail feels and works, adjust if necessary. Use an appropriate fin for conditions and if you manage to get that combo working you will have as much gust response a needed.
Enjoy
Select to expand quoteikw777 said..
And the OP is long gone! LOL!
Homestraight did say
"As a newbie buying first gear it's ridiculous detail to work through..."
and I guess this thread has confirmed that.
Select to expand quoteFez said..
So summing up, put the right mast in the right sail so it matches. Pay attention to the way the sail feels and works, adjust if necessary. Use an appropriate fin for conditions and if you manage to get that combo working you will have as much gust response a needed.
Enjoy
Amen! 
Select to expand quoteterminal said..ikw777 said..
And the OP is long gone! LOL!
Homestraight did say
"As a newbie buying first gear it's ridiculous detail to work through..."
and I guess this thread has confirmed that.
Select to expand quoteTe Hau said..Homestraight said..
Why do neil pryde have flex top masts when most others are constant or hard. Does neil pryde handle gusts better with flex tops?
I've seen a nice Maui sail but that means buying at least a constant curve mast. I've already got boom, base and uxt extension by NP just not mast and sail.
As a newbie buying first gear it's ridiculous detail to work through...
Help appreciated... Noting I already know neil pryde and maui/severe/gastra generally don't match... Have seen the table.
Here's a bit of information overload for you.
I copied it from a website a few years back.
The author (A Scandinavian Formula sailor) did a lot of mast testing and appeared to have a bee in his bonnet about incorrect info from manufacturers.
In particular he mentions Maui Sails and it appears he was correct.
Maui have just recently announced their new mast line and the change is to 'Constant Curve'. Suggests the previous Maui masts were not.
Personally, I've measured many Maui masts (my sails since 2005) and they are always 'hard top'.
Nevertheless, a lot of good insights here........
Stiffness.
Measuring how much the mast deflects related to the length, you have a figure for the stiffness of the mast. When a mast is imprinted with say IMCS 32, it is the stiffness that are referred to. The bigger the number, the more the stiffness.
Bend Curve.
If you measure how much the mast deflects at the 1/4 point of the mast, at the midpoint, and at the 3/4 point you get some figures telling of the way the mast are bending under load (called bend curve or bend characteristics). If we for instance say that a mast deflects 13 cm at the 1/4 point, 20 cm at the midpoint, and 15 cm at the 3/4 point, you find your calculator and do as follows:
First you calculate how much the mast deflects at the 1/4 point in % from the deflection at the midpoint. In our example it's (13 x 100 / 20) = 65 %.
Next you do the same calculation for the 3/4 point - that is the deflection of the mast at the 3/4 point in % from the deflection at the midpoint. The calculation is (15 x 100 / 20) = 75 %.
Now all you have to do, is to subtract the two figures - that's 75 % minus 65 % = 10. To be correct, the denomination is not 10 % but 10 %-points. Anyway, you say that the mast has the bend curve of 10 *).
To make it easier to understand the bend curve figure you can translate the figures to these IMCS terms:
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 misleading use of bend curve characteristics of (some of) the companies.
It is evident from the scale that "Constant Curve" doesn't mean that the mast is equally soft (or stiff) from the bottom to the tip. Constant Curve means that if you hang a weight of 30 kg from the midpoint, the mast deflects 10 - 12 %-points more at the 3/4 point than at the 1/4 point. No more - no less. You can't say that a mast is "relatively Constant Curve" - as heard from a well known sail designer in an excuse of his top stiff masts.
In spite of this lack of room for mistakes, almost all masts from the companies are called Constant Curve - wether they are or not **). Perhaps this is so, because there is most sale in telling that the masts follow a middle course. The underlying message of the companies is that the mast has a standard bend curve, so that it fits all modern sails. But often it is misleading *), and the buying of a mast according to the inaccurate or perhaps immoral playing with names that - as we saw above - is in fact precisely defined, has cost many a windsurfer lots of money for no good.
For instance, Gaastra, Fiberspar (the longer masts) and Maui Sails masts are all very stiff in the tops (most often placed between 5 and 9). These masts are specifically made for the companies own Vapor (former Nitro and Neutron) and TR sails. The masts are not Constant Curve - in spite of the pretence - and they mostly only fit to the sails mentioned ***).
A couple of years ago Neil Pryde had a pretty sofisticated way of spreading fogs: They published some "Bend Offsets", which (when you calculated on the figures) placed the masts in the middle of the Constant Curve scope. The figures obviously more reflected a kind of "calculating backwards" to get the wanted results, than they reflected genuine measurements. A more recent Neil Pryde trick is to indicate approval to the IMCS system by telling the IMCS stiffness (say IMCS 21), whereupon they - without any defintion at all - name the bend curve "Progressive Flex". Are you confused? No need to be - just remember that the Neil Pryde masts are pretty soft on the tops (most often placed between 14 and 17 ****)), and that they are specifically made for Neil Prydes own sails. The masts are not Constant Curve, and you can't use them in many sails from other brands.
What's most important - stiffness or bend curve?
What to look for - stiffness or bend curve? Unfortunately we get no help from the companies that (besides their empty way of using the phrase "Constant Curve") only inform us about the stiffness of their masts (say IMCS 32). And - as we saw - the stiffness is far from the whole truth about the masts. In fact you could pretty easily argue that information about the bend curve might be more important. Since the stiffness tells something about when the mast starts working (at what load), the bend curve tells something about how the mast shall work when loaded.
How does the soft and the stiff areas of the mast influence the appearence of the sail?
Working in the sail, the mast of course deflects the most in the softest areas of the mast - and deflects least in the stiff areas. Where the mast deflects the most, it pulls away from the leech - in this way straightening the sail (with little depth) on level with the soft area. If the sail has a camber inducer at this place, it often rotates easily - or perhaps it is even not pressing properly on the mast.
Conversely, the stiff areas of the mast shall not move a long way from the leech - thereby not straightening out the sail-cloth on level with this stiff area (creating lots of depth). If the sail has a camber inducer at this place, it most often presses hard on the mast - often to a level at which it's difficult to rotate. And when it rotates, it is often accompanied by a loud "camber-bang."
The same sail rigged with a Flex Top and a Hard Top mast respectively.
If we think of rigging the same sail with the two mast-extremes respectively (for instance a Neil Pryde mast with soft top and a Maui Sails mast with stiff top), we shall try to predict the differences. It's important to note that this is not science - just a kind of common "knowledge" among the gang of old windsurfers from the local beach:
With the Neil Pryde mast the sail shall have a big depth (much profile) in the bottom and in the middle of the sail, while the top of the sail shall be pretty loose. Often the change from the area with big depth to the loose area shall be very "sudden" with a lot of wringles. The center of effort shall probably be placed forward (and deep) in the sail, and the camber inducers shall have a lot of pressure. Actually it could be necessary to remove a couple of spacers - or to file off some of the plastics - to make them rotate. As the mast is pretty stiff in the middle sections, a lot of downhaul is probably needed.
With its loose top the low-end pull from the sail comes from the deep profile in the bottom and the middle sections. And often the angle of incidence around the mast pocket shall be pretty rounded, so that the air flow over the sail shall be very attached and make it easy and steady to sail.
With the Maui Sails mast the sail shall appear pretty flat (little profile) in the bottom and middle sections, and the top shall not be very loose. The change from the flat bottom to the not-especially-loose top is spread over a large area, and the sail shall have a rather harmonic appearence - gradually twisting towards to the top.
The center of effort shall probably lie a way back, and the camber inducers most often shall not press very hard on the mast - in fact sometimes you shall have to place some spacers between the battens and the inducers. As the mast is relatively soft in the middle, you shall probably not use a lot of strength to downhaul the sail - and using too much downhaul force might almost collaps the sail in the middle.
With the flat bottom and middle sections of the sail, the low-end pull are caused from the relatively tight leech high up the sail - and from the fact that the center of effort is placed a way back.
Often there's a tendency that the angle of incidence around the mast pocket shall be rather "sharp" (the sail is almost cutting its way through the air), and in this way it is pretty easy to over-sheet the sail. As the air flow over the sail is always at risk of being turbular, it is easy for the sail to loose its power. A sail with a sharp angle of incidence might be exellent for very good sailers, but for us mortals it might be a little nervous.
Some findings when measuring masts.
Here is a link to some measurings of masts. Even if the measurings shown are selected, the figures are still mostly raw data - but here under you'll find some of the simliplified and generalized conclusions, you can make from the material:
*
The mast neither changes stiffness nor bend curve, as the temperature changes. Even though you by means of the IMCS test can't find any difference, if it is 0 degrees celsius or 25 degrees celsius, of course you might speculate, if the mast perhaps gets a little "slower" in the lower temperatures - that is if the "flex response" is dampened.
*
If you shorten the mast (from the bottom!), it gets softer and doesn't change its bend curve. Of course it's not wise to cut off so much that the mast foot/extension doesn't fit the mast - or that the boom is fixed above the extra strong boom area. And as indicated - never shorten the mast from the top.
*
If you extend the mast it gets stiffer (most with Flex Top, a little less with Constant Curve and least with Hard Top masts), and it almost doesn't change bend curve. Of course you shall not extend the mast so much that you clamp on the boom below the strengthened area.
When you try to find a way to calculate, what approximately happens to a mast that you extend, you'll have to decide what you'll understand with "extending". For instance, how long extension are we talking about (in numbers or relatively)? How much extension in the mast are we talking about (in numbers or relatively)? What is the stiffness of the mast to extend? What is the bend curve of the mast to extend? And so on and so forth ...
If we make a fast decision and say that we are talking about a 30 cm extension of the mast by means of a 50 cm extension device (that's of course 20 cm up in the mast), then - based on numerous measurements - you can (very) roughly say that ...:
*
All masts keep (approx.) their bend curves when they are extended.
*
All masts become a little stiffer (according to the IMCS standard) when they are extended.
*
Hard Top masts become relatively least stiffer (around 2-3%).
*
Flex Top masts become relatively most stiffer (around 6-7%).
*
Constant Curve masts become stiffened up between Hard Top and Flex Top masts (around 3-6%).
This can roughly be "translated" in this way ...:
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If you extend a Hard Top mast with 30 cm, so that it reaches the length of the next mast in the line, the extended mast is supplied with 1/6 - 1/4 of the extra stiffness necessary to get on level with the next mast in line.
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If you extend a Constant Curve mast with 30 cm, so that it reaches the length of the next mast in the line, the extended mast is supplied with 1/4 - 1/2 of the extra stiffness necessary to get on level with the next mast in the line.
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If you extend a Flex Top mast with 30 cm, so that it reaches the length of the next mast in the line, the extended mast is supplied with 1/2 - 3/4 of the extra stiffness necessary to get on level with the next mast in the line.
The more mast with or without extension that are measured, the more precise the ability to predict what happens as to change in stiffness - and the less likely it is that mentioned general rules have to be changed.
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If your mast has become "excentric", this doesn't change the bend curve significantly. However, as the mast now is a little "pre-bend", it equals it has grown a little softer.
There is a tendency that the increasing softness that follow heavily use, are most noticeable in the areas that work the most - that is the top of the mast. But - you have to use the mast very much, before you face any problems in this respect.
In short, paring mast with sail (race sail/race mast).
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If you use the mast the sail producer recommends, you don't risk anything.
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Never use a Neil Pryde mast with a Gaastra or Maui Sails sail.
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Never use a Gaastra, a Fiberspar (the longer masts) or a Maui Sails mast with a Neil Pryde sail.
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Think about it, before you use any of the obove mentioned ("extreme") masts with other sail brands (North, Severne, Gun, Naish, Sailworks, Aerotech etc).
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If you choose a "detuned" Gaastra or a Maui Sails mast (for instance the Maui Sails SRS 75 % mast), there is a tendency that these masts fit in the Constant Curve scope. The same is true for the older and longer Neil Pryde Freeride Pro masts.
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A lot of 100% carbon masts are manufactured in two Italian plants. Even if the sail producers say that they order their masts from their own specifications, it is a well known "secret" that you might be lucky enough to buy a a cheap mast (for instance a GUN Dominator) with IMCS numbers that is hardly distinguishable from the numbers associated with one of the much more expensive masts from one of the well reputed (and expensive) sail producers (Neil Pryde for instance). Of course this is just an example!
Footnotes.
*) There is a little further information to get in the calculation for bend curve than just the figure ("10" in the example). If you compare the 1/4-deflection and the 3/4-deflection mentioned (65% and 75 %) with for instance deflections of 63% and 73 %, you'll end up with the same bend curve figure. However, intuitively you might see that the 65/75 mast is a little more "U-shaped" than the 63/73 mast, that is a bit more "V-shaped." Admitted, this is perhaps a little nerded.
**) There are exceptions - Sailworks seems to be honest about their masts.
***) The new sail designer for Gaastra (Dan Kasseler) came from Naish Sails, where he designed sails around some (probably) traditional Constant Curve masts. At Gaastra he inherited the top stiff masts from Barry Spanier and Phil McGain, and he has built the new Gaastra race sails (the Vapors) around these masts. Kasseler says that he'll continue to design sails around those original Gaastra (former "Ignition") masts - but let's see ... At Naish Sails he had a great success building sails around traditional masts - for instance the sail that helped Finian Maynard making his World speed record in the autum of 2004.
In an all new video at the Maui Sails homepage, Phil McGain one more time tells us that his SRS 100% masts are Constant Curve. But the truth of this statement doesn't grow with the reiterations of the falsity. Maui Sails race masts are and have always been Hard Top - Constant Curve!
****) The bend curve of the longest (and seldom used) Neil Pryde race mast (the X9 580) is placed around 12.
Going off this my sailworks & severne masts (21) are flextop or super flex top? I thought they were constant curve..
Most of my masts are around 19-21 IMCS..
IMCS 21 refers to mast stiffness, not bend curve. Sailworks masts as far as I am aware are 64% base, 76% top so a constant curve 12, but I could be wrong.
Select to expand quotemr love said..
IMCS 21 refers to mast stiffness, not bend curve. Sailworks masts as far as I am aware are 64% base, 76% top so a constant curve 12, but I could be wrong.
Dur..ok. Sounds right..
