BSG Développements February, 2008 http://www.bsgdev.com Contact: contact@bsgdev.com

The SailPack meshing method A developable surface is a ruled surface defined by straight lines named generative lines. A ruled surface, (then developable) has the quality to be flatten. With the SailPack meshing tool we are going to describe the surface of the mould between seams by ruled surfaces. The outline of these surfaces will be curved by broadseams. This process is automatic in the software. Are following in this document :

- Operations around a “zero broadseams sail” you have to follow with sample SailPack files. Please, copy the directory named “Meshing Method files” in your project folder and launch SailPack.

- Some case of classic mistakes and the solutions.

- 1st step: Conic sail, parallel seams A cone is a ruled surface (so developable). We define a conic triangle with panels; we should obtain zero shape panels. If we design a mesh which results to non-zero shape panels, it means that the approximation of the mould surface made by the meshed surface is not correct. Select Actions menu / Project-Boat, open the folder “Meshing method files” Select Boat config named “Cone01” Load New Sail “NoProfileNoTwist”. This sail is a triangle with only one profile at the foot. Associate it to the LOWASPECTRATIO geometry (drag and drop). We are going to switch between 2 graphic profiles: one is “Skeleton” >> you can built this profile in the top right of the 3D Window : Select Options / Save config and enter the name of the profile “Skeleton”. Go in the Shortcuts window and turn off all the buttons (except Perspective) and turn on : Boat/Mast, Maille, Verticals, Triangle, Skeleton. Save this profile on the top of the 3D window, select Skeleton/save The second graphic profile we’ll use is “Mesh” >> you can adjust this profile in the top right of the 3D Window : Go in the Shortcuts window and turn off all the buttons (except Perspective) and turn on : Boat/Mast, Maille, Net, Triangle, Skeleton, Panels Save this profile on the top of the 3D window, select Mesh/save Select the “Mesh” graphic profile Open in Actions menu the Panel Layout, go in the Tab “Seams” Create a cutting script with seams parallel to the foot and fabric width 1.37m Select View options: show Broadseams and Calculation control Select meshing method “Seam to seam” At this step, 3D window and Panel Layout should show this: The situation is: The direction of mesh lines are exactly the same than the conic generative lines, the sail surface is perfectly approximated by the meshed surface.

This surface is developable; there is no broadseam between panels. This surface will be our reference during the following exercises. From a sail making point of view, broadseams calculation is perfect but you should note that except at the seam’s intersection with the outline, we have no intermediate points to draw luff and leech. Now, Select meshing method “Automatic”: Meshing lines become perpendicular to the seams and some broadseams appear in the upper part of the sail. What’s happened? Try to move the 3D view in order to obtain a grazing view of the top luff:

he mesh does not describe exactly the conic surface, some hollow appear between

n a sail making point of view

Tseams. The broadseams calculation is correct and describes a surface made of bumps and hollows. O , we are happy because we now have intermediate

to

elect meshing method “Parallel”, move the red point of the calculation control line to

points on the luff but we are disappointed by the wrong broadseams. We are goingchange this mesh. Sthe middle of the foot and the blue point in the height of the leech in order to obtain a small angle with the luff. (In order to see the calculation control line, click on “Show”/”Calculation control” in the “View options” section).

In that mode, the meshing lines are parallel to the calculation control line. With that functionality you have placed the meshing line in a position very close to the perfect orientation (for this seams layout) which is radial head like generative lines. On a sail making point of view, there are intersection points on the luff which increase the panel outline definition and avoid the second layout process. The mould surface is well described by the meshed surface. The broadseams calculation produces no value more than 0.5mm. Here is the value of the compromise we did to have a better definition of the panel outline. Actions menu / Geometry Associate Sail1/NoProfileNoTwist to the HIGHASPECTRATIO geometry (drag and drop).

The angle of the calculation control line remains the same, then the mesh surface and broadseams calculation are identical despite this important modification of geometry.

2nd step: Conic sail, tri-radial seams layout We are going to design a radial zone seams layout on this conic sail. We will look for a mesh surface which is the best compromise between sail making constraints and mould description. The evaluation of the compromise will be the value of calculated broadseams knowing that the perfect value is zero (developable sail). - Open in Actions menu the Panel Layout, go in the Tab “Seams” - Cut horizontal zone and select the seam - Open the Edit pos. dialog box and enter 30% for the blue- - point, 70% for the red point - Select the upper zone and cut an horizontal zone at 50% - Select the lower zone and cut a vertical zone at 50% Select the tack zone Open the Cutting script dialog box Select the Radial Tack script Enter 15mm for seam width Enter 0.45m for the fabric width Do next and Stop Select in the 3D window the Mesh graphic profile In Panel Layout, View options, select Show broadseams and show Calculation Control

The default for the Meshing method is “Automatic”, you should have this screen:

The approximation by the mesh of the mould surface is not perfect. That is the reason why we have broadseams in the radial (remember we should have 0 because the sail is conic). There are some steps on the zone seam and the surface seems very sharp. Now, select Meshing method “Parallel” Drop the blue point in the middle of the foot edge and the red point near the luff side of the first horizontal zone seam. With that angle, we obtain a better description of the mould (mesh lines close to the generative lines of the surface); all the broadseams values are close to zero.

On a sail making point of view, there are intersection points on the luff which increase the panel outline definition and avoid the second layout process. The mould surface is well described by the meshed surface. The broadseams calculation produces no value more than 0.5mm. Here is the value of the compromise we did to have a better definition of the panel outline. Negative broadseams are visible because the mesh straight lines describes a surface which is inside the reference mould surface and so create some infinitesimal hollows between seams. Apply a Radial clew script in the clew zone The default automatic meshing method is correct in that case because the general camber is not important in that zone - Apply a Custom cutting script in the middle zone - Click on the start1, End1, Start2, End2 reference points - Input 20% to move the Start1 reference point in order to bend the panels (for example…)

he “automatic” meshing method is making a good description of the mould surface Tin the leech zone but in the luff zone, the sharp edge between luff panel and the n°2 builds an artificial broadseam value (1.4mm). From a sail making point of view, the junction between the tack zone and the middle zone presents steps and we will struggle to have a smooth zone seam. Now, selectDrop the red point in the m

Meshing method “Parallel” iddle of the bottom edge and the blue point in the back of

the upper edge.

With that angle, we obtain a better description of the mould (mesh lines close to the generative lines of the surface) in the luff zone. All the broadseams values are close to zero, despite the difficulty in that zone, due to the panel proportions (the height of the panel is important regarding the height of the sail). On a sail making point of view, there are enough intersection points on the luff which increase the panel outline definition and avoid the second layout process. The mould surface is well described by the meshed surface. The broadseams calculation produces no negative value more than 1.2mm (which could be not considered during panel assembling). Here is the value of the compromise we did to have a better definition of the panel outline. We guarantee with that mesh a perfect junction between zones. - Apply a Radial head cutting script in the head zone with a parallel meshing method

Conclusion : We built a mesh surface for the whole sail. The perfect description of that developable mould should give zero broadseams. The approximation of the mould results here in some very small broadseams.

If you associate this sail on another sail geometry (LOWASPECTRATIO for examplthe mesh is the same and broadseams calculation are still correct.

The following steps are to insert intermediate profiles and outline curves to shape a non conic sail. Broadseams will be calculated in the part of the sail where the mould surface is not developable. In case of zones which often stay developable like around the tack, broadseams values move between negative and positives values close to zero.

The mesh is part of the seams layout. The proper method is to develop mesh and seams layout together and to save this file as a model of seam layout.

When you have to design a new sail, you just load the seams layout and the mesh will be correct.

e)

3/ CaseA : Small dinghy Sail, only 2 seams

We receive this sail with this mesh and these seams layout :

By moving the 3D view, you can identify the first problem :

The mould is not well described by the mesh is full of hills and valleys. The case is not easy because not enough seams and the mould is powerful…

1st step orizontal seams in the bottom : : I propose to change the mesh to obtain more h

The calculation control seam has been moved …. … and the angle of the mesh too. The bottom of the sail is now well describe by the mesh.

… But the problem is now on top because the mesh is not enough vertical :

Step 2 : I propose to change the Mesh calculation control mode in “Orthogonal”

The mesh is now Orthogonal to the calculatio … to obtain horizontal mesh in the bottom and more vertical mesh to the top, you will have to curve the calculation control seam :

n control seam.

The mesh became quite radial. If you curve too much the calculation control seam, you will have wrong panels calculation and perhaps execution errors of the software…

Now, the mould is well describe despite the small ns solved!

umber of panels. The panel geometry issue i

2/ Case B : Triradial sail, curve seams, automatic mesh calculation Problems of mesh again… a very important thing to understand is that panels outline (seams) and zone seams are drawn on the mould surface. This following mesh is designed to go straight from seam to seam. When a mesh line cross a zone seams, the intersection point goes up “on the mould” and describes a step from the flat part of the panel and the zone seam. Here is the sail :

The orientation of the mesh is not correct to describe the mould, mainly on the luff which is totally flat except on the zone seams. Here is the guarantee that you will struggle to stick these zones.

The problem is here

I propose a new mesh. The principle is A/ you must describe the mould. For that, you need vertical mesh on the luff in this case. Generally, try

/ You must design a smooth mesh from zone to zone to have fair seam zone to assemble.

licated because the curved seams. I shared the middle zone in three to orient properly the mesh intersections with the curved seams. Note that this work on the mesh is definitively associated to the seams layout and has not to be don er sail.

to orient the mesh line parallel to the generative lines B/ You need intersections between the panel outline and the mesh in sensitive zones : luff and zone seams. C This case is comp

e again if you “load” this layout on anoth