Sail Setting Optimizer - SSO

Very seldom, except once in 2005, the Sail Making argument was discussed on this forum. The same argument receive poor attention/interest in many others forums as well.


I noticed since long that the Sails, while being the engine of our models, do not receive the same attention as the for Hull/Fin/Rudder design and construction.

In the picture an example of the typical tools used to manufacture the sails :
Generally once the sail are made, the modelers check visually the forms according to their personal criteria and after are integrated to form the RIG.

Tuning will consist to adjust the sails in accordance with the perception obtained during the boat sailing.

Probably, no one know what is the Lift Force (kgf or Newtons) that the sail/rig will produce at any time.

The knowledge of the Lift Force produced by the Sail Rig will probably, in my opinion, offer more indications on how to Make and Adjust the sails as function of wing strength and direction.

Should be interesting to knows that our models have the sails set for maximum lift power and if racing results are not achieved is because the problem may sit somewhere else !!!

The idea to measure the lift force provided by the sail is a long standing desire.

It is my intention to introduce here the new tool designed in collaboration with my friend Pierre.

This tool is called by Pierre 'SSO’ and stay for Sail Setting Optimizer and it is based on a simple dynamo-metric principle.

 Of course is not a sophisticated wind tunnel with plenty of strain gauges but the SSO aim is to be a simple rudimentary tool with intrinsic reading imprecision's assumed to be a constant error and therefore sufficient to detect sail adjustment variations. Only once manufactured I could be more precise unless is a fiasco !!

On our models, the lift force may vary from 0 up to 3kgf or 30N as function of surface and wind velocity.      

The SSO is not yet constructed but some hardware investigations are already made like the choice of the Dyna-meter (35€) and 2 Blowers of 35cm (70€). For this design I decided to use a simple Mechanical Balance with analog view.

Tests with a blower without grid show very little oscillations instability of the needle, this was the initial fear that the Blower’s Air flux would produce large oscillations as such to hide the step variations due to sail adjustment.

The other important feature, not verified because not yet available, is the use of linear ball bearings to reduce at the minimum the sliding frictions of the Rig board. The sails can be adjusted via independent Servo winches. I invite everybody to comment or suggest other options or design.


Here the basic principle :

I like it. Only a small recommendation, move the servos out of the way so you can mount a deck stepped rig with shroud lines. Then you can test a variety of rigs on one platform. Plug the mast into the hole or plug the hole with a plate for deck stepped (I guess you’ll also need some deck plates).

Another idea is to measure the forces with a joystick under the testing platform. That way you get capture the direction of the forces. Certain sail designs or trim settings may maximize forward force at the expense of higher than desired lateral force. Or hang the whole device fore & aft so the “boat” can heel. And then just measure heel angle.

Can’t wait to see the results of testing.

Hi Tallastro,

for the moment I need to confirm the principle and keep the system a simple as possible. This is the Step 1.
Supposing that the SSO will prove to be a good and simple way to check the sail power, then I could jump to Step 2.

Step 2 is actually considering to replace the actual “sliding board” with a “boat cradle” where the full boat, including appendices, could be mounted in.
RG65 , IOM and Class M are the models considered.

There is already an other project SSO-3 that make use of a water tank where the boat can also tilt, although is not important for the purpose, but for the time being is abandoned because of handling and transportability. Of course each one could make it at home as a fixed structure. The so called “rollers” are there to avoid tilting and improve measuring data collection. Frictions are reduced to a minimum compared to linear bearings !!!
see attachment :


BTW, I forgot to tell that the idea to make similar ‘gadget’ dedicated to rigid sail was already presented here almost 4 years ago : Prototype

I discovered this site only 15 day ago navigating on the web via another French forum.

It is very interesting that two persons separated by the ocean are working on the same idea, although not for the same purpose, one for soft-rigid sail comparison and one for soft sail lift power overall.

The world is getting smaller every day !!!

The principle remains the same.

In this article, that deserve good attention, it is mentioned also RCsailing Forum where Nautibuoy, Dick Lempke, LincolnR and Morspeed were involved
in the :

I fill comforted by the fact that Nikolas Osvalds did not made any remarks about the reading precision of the balance and needle oscillations due to air flux instabilities and vortex as such to jeopardize the project.


PS: added wind screens to simulate the water level

Possibly something for you once you get to adding a cradle for the actual boat…

You could track the effect on the deck angle as the winds etc intereact with the sails?

Thanks, but with electronics is getting complicated and afterall the resolution provided by the accelerometers is far too high compared with what needed - KIS !!!

Hi ,
I told myself that probably could be a good idea to show the principle with a full rigged boat. The supports can be changed in position and shape depending on the model.
The important point is to find for each model the “pulling point” (general CG) on the Fin where to attach the string holding the weight lying on the balance.


Another possibility to tilt the model with dedicated supports :

The central Red dot is the point where the pull string is attached to the Fin and represent the Overall CG.


So the wind hits the sails and slides the boat forward, pulling the string giving you a weight reading?
Different jigs to set the boat at various angles so you can fine tune sails for specific situations or as an all-round option?

It would be more complicated but if you set a few bearings running the length of the hull on each side with a flat surface to mount the stands on, you could get a very smooth surface for the boat to run on with very little friction. But I suppose KIS?

Would turbulence from the wind shield not be an issue? Or is it fine as long as the major flow from the fans is above it?

Further you may test various manufactured sails with different parameters like different Draft, Draft position, sail form, etc. , all what is needed to make a good sail for a particular wind range. see eg. :


To check the Blowers capability to produce the wind needed like 5, 10, 15, 20 kt, I prepared a test set up composed of 3 Blowers and a light panel of 50cm x 100. Assuming the blower possibility to generate a wind speed of 10kt, the measure on the Balance should be around 917g. To explain that the balance is initially supporting a static load of 3kg (full scale) therefore the wind pressure force will produce a lift and reduce the marked weight to 2.083kg. The blowers container include a grid aiming the vortex reduction.


PS : The balance actually used is for 3kg therefore for higher wind speed it will be necessary to use different weight balance close to 6kg to test Class M Sail Plan.

I went buying two other blowers for 79€.

prepared a drawing with dimensions showing the blower’s boxes. A separation box could be used to increase the height of the blower’s column.

On web I found this interesting link : Testing.html

And I wonder if the grid could be composed only with vertical ‘blades’.


The wind source is actually the major concern.

Some experimental work and papers readings suggest to create a trapezoidal box equipped with vertical vanes.
The trapezoidal form is a sort of venturi that should produce an increased wind speed.
The actual trial show with an manual anemometer a speed that can reach some 6 m/s or 11.6kt.

A box need to be constructed.

The Apparent Wind direction is set at 27° from the boat axis, as reported on various books for close hauled course, while the True Wind is at 45°.

The above suggest a ‘wind box’ dimensions with 42cm close to the blower side and an exit window width of about 28.5cm valid for the Class M. See drawings


After various considerations with my friend Pierre, I decided to complicate a bit the Blower Box design.
Tomorrow I will go to buy the stuff needed.
I found, BTW, that making air is not always easy, heheh !! and yet not sure to get what I want !

Sometimes it depends on the food eaten or the beverage you drink. I can make my own “wind” if I eat Mexican cuisine and drink their beer !!! :wink: Sorry ---- I just HAD to reply.

Hi Dick,
Hehehe !! I know that, but sometime words are also moving a lot of air like “words blowers”…!!!

From drawing to hardware !
First module.
Tomorrow some testing and air force mapping with and without vertical vanes.

Some tests carried out today.
I was expecting more wind, but the highest average is 6.0 m/s at 38cm from the blower fan. See mapping below with some seldom pictures.
Interesting to observe a certain down-wash at the base and an up-wash at the top. This phenomenon will help when stacking up the modules.
I do expect of course a speed drop at 60cm from fan.

The Blower box will be shorter from 41cm down to 25cm - Not sure I will use a grid or vertical vanes ! Ball bearing and shaft defined and ordered. The dimensions of these items required the SSO standing support modification with rev.3 Wood part dimensioning details under preparation. The observation made so far will suggest that the air speed adjustment will be different from one blower to the other. Low speed at the bottom and high speed at the top. ClaudioD Attached the Part list of the SSO Bench