Sail Design by Computer Simulation　[For One Design Dinghy]

The sail's shape while sailing is changed by rig setting and wind speed. There was no system for small dinghy to calculate accurately or predict what it would look like in actual sailing 10 years ago.Development in computer technology for these past ten years has made it possible to simulate the flying shape in the computer program developed by North Sails design team.

However this program was developed to be used primarily for the big racing boat like AMERICA'S CUP. North Sails Japan has improved the design and analysis program into one for small boats like 470, Snipe, FJ, Optimist etc. Here we will explain how this deign system works and about the advantages of it.

By simulation of the rig, sail shape and wind pressures in this program, we are able to re-create flying shape (sail shape in actual sailing with the wind) with a high level or accuracy. This is very useful to optimize the design for any conditions. However the accuracy of the result is limited only by the detail of the input information; we cannot predict its flying shape if we do not have accurate in-put data.

For accurate simulation we need to fix the conditions as follows:

rig setting	Sail setting	Sail trim
・mast stiffness ・rig tension ・spreader length and deflection ・shroud position ・stretch of the shroud ・load on the trappize wire (crew weight and height) ・Mast step position	・panel layout ・stretch of the sail cloth	・main sheet ・jib sheet ・boom-vang ・traveler ・cunninngham

・Sailing condition

wind velocity attack angle heel angle leeway boat speed

Set up the sail designed on the mast with all the data in the computer program, and let the air run,

visualizing wind flow on the sail

calculation of the load on the sail according to the wind velocity		deformation of the sail cloth and mast caused by pressure

we can anticipate the accurate sail shape and wrinkle effect in each condition from the pressure distribution or deformation of the rig.

For example, in real life the wrinkles appear along the luff of the mainsails without cunningham tension so it is necessary to set up the mainsail with the same condition. The sail controls need to be adjusted in the simulation just as in real life in all the conditions from the light wind to strong wind.
Here is the simulation of cunningham effect

These diagrams show transformation in sail shape with the appearance of the winkles run on the sails by cunningham control.

Wrinkling on the sails has a big effect on the sail shape. So If we cannot simulate the wrinkles, it means we cannot build the target shape.

This simulation program makes it possible to see and investigate the transformation in sail shape by individual controls like main-sheet, boom-vang, cunningham, jib-track, jib-sheet, outhaul, change of rig setting tension, spreader length, mast inertia, etc. as if it goes in actual sailing. It is possible to quantify the effect of adjusting one control on the sail or a combination of controls.

Comparison between actual sail shape while sailing and flying shape from feedback by calculation

With the software interface you can see the sail shapes simulated from various angles to check the details.
You can move the view point to any position around the rig such as from behind the boat, from above the rig, helmsman's view, below the boom, etc.
By comparing the photo taken while sailing to the image built from
simulation with the same condition as sailing, we can identify the difference and correct the design until the flying shape and the simulation become identical. This makes it possible to optimize the design as the sailor requires.

We are one of the special lofts who use sail simulation for the one-design small boat sail and rig development and sail shape optimization for specific conditions. This is why many of the world's top sailors put complete trust on us to succeed in the Olympics.