I have been learning quite a bit about sailing from this site and about what makes the land sailers sail. I have made one LLF mini with a tyvek sail, all from information and plans that I got here.
While I am learning a ton, I still feel like there are a lot of gaps in my understanding of how a sail functions and how to go about making a good all-around sail.
I was hoping that some of you could help me fill in some of those gaps.
This is what I know (or think I know) about land yacht sails:
1. Flat is Fast
2. deep sail to start for low end power and then flat when sheeted in for speed
3. When sailing, set sail to the apparent wind
These are some things I am hoping to learn:
1. Why is flat fast?
2. Can I create adequate camber by curving luff only or do I need to broad seam?
I am also including a couple of illustrations here to show what I understand about broad seaming. The first picture shows how I would cut the pannels, the second shows my understanding of where the depth in the sail would be created (red circled areas) when sewn together.
As always, appreciate the input
Bob
Bob I dont profess to be an expert but I believe you are pretty much on the money with what you have written
A flat sail is faster because it has less drag and is turning the wind less Remember that when you are sailing fast the apparent wind is at a very small angle to your direction of travel so a very full sail would just flap when sailing fast However a fuller sail will turn the wind more and generate more power when the apparent wind angle is greater to the direction of travel as can be when you are sailing slower
It sometimes helps to think of the force on the sail is always at right angles to the sailcloth so it follows that the rear section of your sail does not want to be hooked as then the forces on that section would be slowing you instead of assisting you
A fast flat sail probably doesnt need much broadseaming at all The shape all in the luff curve
It has often been said in general sailing that letting the sail out until it flaps and then sheeting it in until it just stops flapping is close to optimum for
ordinary folk Finding the exact optimum for the current set of conditions is something of a science
There are times when I feel I am right in the groove so to speak but its quite often more by good luck rather than good management
Have fun with your sailmaking
bob thats great work. I had been instructed by Marcelo from Foxtrot Velas www.foxtrotvelas.com.ar .the sailmaker in Buenos Ares, that the rear radial half of the sail should be built as completely flat seams with the length of the cloth running along the centreline of each radial panel.
. he and i cut the slightly differently but I think your idea would be just as valid.
of course the summary of flat is fast is too simple. you need to think about the surface you will sail on. our flat saltlake sails are truelly hopeless on a European beach, and cutting a sail for those conditions is a whole other ball game
Beach sand in my experience can be very variable but generally at slow speed it is more draggy than at high speed compared with say bitumen or concrete It follows then that a good beach sail would need to be fuller to generate the power to overcome the drag at the slower speeds
To try and get the best of both worlds running starts are used a lot here in NZ to allow flatter faster sails to even get moving on beaches on
some occasions 
Select to expand quotelandyacht said..
bob thats great work. I had been instructed by Marcelo from Foxtrot Velas www.foxtrotvelas.com.ar .the sailmaker in Buenos Ares, that the rear radial half of the sail should be built as completely flat seams with the length of the cloth running along the centreline of each radial panel.
. he and i cut the slightly differently but I think your idea would be just as valid.
of course the summary of flat is fast is too simple. you need to think about the surface you will sail on. our flat saltlake sails are truelly hopeless on a European beach, and cutting a sail for those conditions is a whole other ball game
Thanks for the input guys. I studied your sail making posts Landyacht, that's where I got the info to build mine although I am sure that my end result differed due to my not understanding the whole process. Could you explain a little about what you mean by, "the rear radial half of the sail should be built as completely flat seams with the length of the cloth running along the centerline of each radial panel."? When I assembled my sail the radial panels did have straight line edges but these edges did not immediately come together because of the slight arc in the back edge of the front panel (refere to the first illustration that I posted). As I brought the radial panels together it formed a bit of depth to the rear, lower section of the sail. I sail on soft sandy beaches up here and need that depth so I think I am on the right path with broad seaming the radial section of the sail. This makes sense for a deep sail but for a flatter sail used on harder surfaces I still have this question:
1.) if camber is created by shaping the luff and puting a slight curve in the trailing edge of the first panel, then what is the reason for cutting the remainder of the sail into radial panels, why not leave this portion of the sail as one flat piece?
Thanks,
Bob
Why not indeed ?
A lot of the reason I think is aligning the weave of the cloth with the direction
of the forces when you are trying to make the lightest sail possible
The average sail doesnt fall into that category
Plenty of good sails have been made without radial panels
Select to expand quoteHiko said..
Why not indeed ?
A lot of the reason I think is aligning the weave of the cloth with the direction
of the forces when you are trying to make the lightest sail possible
The average sail doesnt fall into that category
Plenty of good sails have been made without radial panels
Makes sense, that's helpfull. I just found a free download from "Sail Cut Cad", have you ever played around with any of that software?
My amateur sailmaking started with a small book called "Make your own sails ' decades ago
With sections on square sails, scotch cut and all the old stuff that you dont see much now
and I havent progressed from there at all into programs No doubt they are good though
The principles are still much the same though I guess
Just the methods have changed somewhat
the reason for the radial cutting of those panels is to reduce stretching. when I cut up a monofilm sail to get that same long panel the panel is how it come off the windsurfer sail(usually horizontal panels)
