Is it possible to cut a given sail to fit any mast curve characteristics (excluding stiffness)? Or do some sails need certain bends.
What I'm trying to get at, is whether there is any reason why masts are flex top or stiff top? - other than the cynical reason "we cut it like that so you buy our masts"
yep it's posaible to cut a sail to suit any mast curve and stiffness charactistic.
but that's where the grey area starts. sail designers have preferred mast specs that they believe work optimally for a particular sail type and size. They design their sails around this. when you look at a sail range "some not all" go from flexier tops in the smaller sizes to stiffer tops in the larger sizes.
depends on what the designer feels is the best mast/sail combination for a particular use.
maybe, i'm not sure about that.
i guess you could also increase the downhaul and it would make it tighter or use a softer mast or change batten or cam shape/curve as well.
the luff curve versus mast shape i understand is more to do with how the sail sets under ideal conditions and the relationship of draft position and twist.
but that is also built in by use of panel shapping. some manufacturers use more of one than the other. typically sails with straighter luff curves are thought to be more tollerant of different masts. (that's a blanket statement of course).
but again i think designers pick their masts based on what they believe to perform best.
some people believe that hard top masts have a more even twist, some believe that flex top helps lock the power in lower etc, but as you point out luff curve/mast shape can be tweaked to effect these outcomes also.
starting to get over my head now.
There is a topic in the wave sailing forum on sail making by a sailmaker.
I also found this site sometime ago, then lost it and recently found it again, deals with sailmaking and gives a bit of a descripttion about luff curves relating to mast bends and seams. It also shows an example of changing the luff curve to suit another mast. I found it a good read as i am going to try and make one oneday.
Basicly the guy says that luff curve is virtually an upside down shape of the mast bend. I haven't had time to test this on the garage floor yet.
www.sailrepair.co.uk/makingsail.htm
hi lungs,
if it were me i wouldn't bother designing a sail in 2d. 3d gives you a much bigger picture and is faster when designing.
start out with a 2d sketch to get the plan/outline good then go to 3d. it's the only way to go.
i haven't used this software but here is a link. it's free.http://diogenes.jerryweb.org/site/sailcut/en-download/
www.sailcut.com/Main_Page
Thanks Gesty,
I'll have a look, but not much of a tech head when it comes to computers so a bit reluctant to download free stuff after a sh t load of free stuff killed the inlaws computer and if I killed this one I'd be shot.
Interesting stuff sailmaking but probably an expensive way to get a dud sail, will eventually get around to having ago.
Just wondering if after this long absence the head has cleared and you have come to the conclusion that a queen is better than a sutton
hehe,
like all things in life it depends on the wind.
i like to be a queen in a NE'r and a sutton in a SE'r
The shape of a sail is induced and controlled by two methods, luff curve and broadseaming.
Luff curve is the difference between the bend of the mast and the amount of round cut into the luff of the sail, luff curve is the main factor in dictating the overall depth or camber of the sail.
Broadseam is the shape cut into the edges of individual panels of the sail, whilst braodseam does induce a little bit of depth into a sail it has more of a role in where the point of maximum camber lies.
The relationship between the two is very complex and hard to explain for a yachts rig and on a rig as dynamic and flexible as a windsurfer rig near impossible so I am not going to try,
To answer the original question, if you alter the luff curve of a sail to suit a different mast you may have to add or remove cloth to achieve the match, if you do not also modify the broadseaming of the sail when recutting the luff you will find the sail will not be anywhere near the same.
As for the stiff top vs flex top I think different designers have different schools of thought as to how the rig will react with a different mast, so go down the path they like best.
To be clear, I'm not looking to modify a sail that has already been cut.
My question is hypothetically
If you got all the sail makers to agree that a given mast was good, could they all make a sail to fit it?
Or would some of them say, "I make sails in a special way that requires a flex top mast"
From what guys are saying, it seems that it's possible to all aim at a single mast.
yep i understand,
both myself and bundybear have answered that question though.
it is simply they design with a particular bend curve as they feel it is the best choice. there is no conspiracy that it's done to sell more gear.
yes all sail designers could design to one "standard bend curve" but why should they, forcing them to do this is asking those that don't agree with the chosen bend curve to compromise their design.
if you look at australia, both severne and KA use different bend curves. i can't speak for either ben or andrew but i am certain that both those guys are trying to design the best product they can. they would both have fundamental reasons why one bend curve is preferred over the other.
interesting interview with Ben.
But who in their right mind puts a rap backing track to an interview?
If you add a mast tip extension,say 15cms you can soften the feel of the sail greatly.Works especially good on the larger sizes to dump the power and make the sail feel lighter.
I have a 400cm blueline which is recommended for my severne 5.6m,i prefer the stiffer 430cm i think on this size as can feel much more has more pull in the sail.
How do i work out the luff curve of a sail for a given mast if starting a sail from scratch?
The website above says its basicly an upside down mast shape, I tried to see that in the pics below, but turning the mast upside down doesn't seem to match the luff curve even if taking any shaping into account which may be in the body of the sail. (on another sail it does match, but mast and sail don't go well together)
Also how much mastbend to apply or is it all trial and error.
As mentioned above the relationship between mast bend and luff curve is what gives most of the shape and the broadseams just determine where the draft will be,so does this mean that a sail will work without any broadseams?
thanks
Very Tough question to answer Lungs. If you are looking at making your own sail without the aid of an expensive computer design program it is far easier to copy off an existing sail you like, simply pin the sail out flat on the floor and measure the luff curve then rig the sail and measure again in the rigged state. This should give you a set of numbers that indicate how much "extra cloth" there is being pushed back into the body of the sail in the form of camber.
Simply pulling the tip of the mast towards the base and tracing around the bend will do nothing for you as a windsurfer mast does not simply bend fore and aft but has a fair portion of side bend in it as well and everything inbetween. Also your downhaul tension on the sail does not simply act upon a straight line between the base and tip of the mast.
The Luff pocket, the skin tension of the sail and even the boom all have an effect on how the mast bends in its static state and in use.
I attempted to make a cambered race sail many years ago when I was an apprentice sailmaker, I abandoned the project after multiple recuts as I could not get it to work right.
