1.2.3. - "esterel"

After the confirmation about the sailing performances of the 123 prototype, even with some remarks about sails, this is the new discussion that continue as “follow on” of the original design.

The new version I called “ESTEREL” from the sea side area closed to Nice-Cannes region :



Start with preparation and epoxy bonding of the false plywood deck 3mm thick.
As can be note, no reverse bow for this female mold. It is not excluded a modification for a second two parts female mold among others implementations as bowed deck a roof.


I will never forget this name Esterel Massif being mountain range is south-east costal part of France that you personally showed me, that have soil and rocks in the mountain range of volcanic origin, composed mainly of porphyry, which I understand gives the hills that distinctive red colour that flows from the mountains into beautiful bays & beaches in the region.

Following my visit the name “Esterel” now has three meanings for me, 1) it represents location of your home and 2) the red hull colour represents the volcanic red colour in the region and 3) the name Esterel is also given to programming language for the development of complex reactive systems suited for model design, which in my mind represents your supreme model boat design and building skills.

All these are the 123 ingridents of the prototype project now given a boat name Esterel that I know will be the very best in model boat design, construction & sailing and your legacy to the model sailing community for many many years to come.

On behalf of all the people who will be building Esterel and enjoy sailing her in the future, I want to thank you in advance in sharing your gift with us.

Cheers Alan

Tanks a lot Alan for the words, probably you have discovered part of my way of thinking.
Passionate for white sail on the sea since little boy, like being the symbol of freedom !.
Learned only a little of the infinite sailing subjects.
As retired it keep me occupied and as you says well, I like to share my limited knowledge with others hoping to transmit my passion.
I always liked experimenting and the boats are good laboratories !

ESTEREL is a small area of my region that got a large impact on my subconscious since the first time I discovered it several years ago. Today I’m very happy to leave so close.
ESTEREL is the name I decided recently to give to my last design. It may happen that “Esterel” will be the name given to a series of models of various size, as recently found out with you in Cannes when I discovered the ‘Moro di Venezia’ !!! hum !! that was a Maxi Yacht and not the red/white America Cup boat of San Diego.
With the actual ESTEREL, the 123 will be kept on the sails. One day could be ESTEREL with ‘M’ on the sails or RG65 or what else.
Thank you again

False deck bonded.
Soft sanding with 800 grade.
First wax !

Dear Claudio,

It’s working, you do indeed transmit you passion! Also, it requires a good understanding of a subject in order to realize its complexity, and appreciate its difficulties. Your “limited knowledge” is only the proof of your wisdom.

I was a bit surprise to learn that your first Esterel will use the previous hull. I guess this is a great token of its high balance and performances. Can you give us then a preview of the novelties you intend to introduce on this first Esterel, and the rational behind them?

Thanks again for your contibution to the R/C model sailing community.

Hi Sylvain,
indeed the test made with the wind range of last week from 5-6kt at the beginning up to 12-14kt with gust up to 15-16kt gave me the insurance about the model quality.
Before that test I was supposing to introduce eventually modifications like the “reversed bow” as well a “flared bow” to tackle the pitching effects.
The wind was sufficiently high to keep on track the boat, therefore non pitching observed. I do not exclude that with lower wind force, it could happen, thus, there is a provision to add, close to the bow, an internal ballast adjustable up to 200g.
This option imply a water plan sink variation of about 1.5mm and a LWL increase of about 12mm.
This configuration is very close to the launch testing condition because of the actual prototype weight of 4230g.

The other modifications, under analysis, concern the type of servo configuration to be used. The image in the film when the Eurgle servo didn’t managed to pull the main is still impress in my head. I used two separate winches just because I was fearing that event !
On the other hand, until I’m not sure to keep the construction weight sufficiently down in order to have margin for an MRG servo, I’m searching for a back up solution including cost reduction.
The simplest solution for the moment is the servo arm, another is referring to a modified servo with a large drum.

That’s for the moment !


PS : I was passing the material order to make the mold, when my supplier proposed a very good polyester filler that allow a super finish with 1500-2000 grade sanding paper. I stopped the wax application after the second layer !

This is the starting point for the servo choice,
Document prepared with Word.


The ESTEREL Boom Plan is depicted below.
This plan establish the sheet length required and consider the two servo options :

It result that a 24kg servo arm as detailed in the drawing is not sufficient to control the sail area of 0.77m² under 20kt of wind and this is explained below .

Here the schematic I use to calculate the power needed for the servo arm.
The sheet length according to the ESTEREL configuration is 270mm
The servo have generally a swing angle of 120° .
With an arm of 79mm is obtained 136mm travel.
Since a dual pulley is used the total sheet length obtained is: 136 x 2 = 272mm
With that configuration the pulling power is also divided by 2.
The pull force calculated from the wind pressure graphic is 6.5kgforce with 20knots wind speed.
Because of the Main boom arm lever principle , the pull force required at the anchoring point is : 1.44kg force.
It is necessary to consider that the servo power is given for no load conditions and friction of the circuit, there fore I take a multiplying factor for security of 1.5.

Thus under such conditions I can establish the servo power needed :
1.44 x 1.5 for security x 2 because of arm dual pulley x 7.9cm arm length = 34.12 Kg.cm

To reduce the servo power, it is possible to increase the distance from the Main boom pivoting point.
In that manner the Pull Force at the anchor point is lower. There is a drawback because the sheet length increase and therefore it is necessary to increase the arm length or increase the swing angle. To note that over 140° swing the system loose efficiency.

Another important consideration is the direct Bernoulli formula application. The wind angle of attack is not included since the the formula is referred to an orthogonal plan.
I personally have a sympathy for the formula used for the Kites depicted in previous post where the sine of the angle can be introduced.
Which of the formula is more realistic for a sail I’m not sufficient competent to tell.
Probably there are some additional margins there too.
Any competent advise will be useful !
Thank you

The amount of pressure on the sheet is at maximum at close hauled. It drops significantly for halfway out (beam reach) and approaches zero for full out (dead run) - especially if the boom hits the shrouds.

As the pressure is greatest at close hauled, it is important to align the sheet along the servo arm, such that the pressure is aligned with the bearing of the servo and not relying on the electrics. Another advantage of getting the alignment is that it provides automatic fine tuning at the close hauled position and becomes coarser as the approach angle increases.

One problem with converting an arm to a large wheel is that the force is never aligned, as it is tangential to the wheel and always exerts a force on the electrics of the servo. There is a way to set up a wheel for reduced pressure on the servo that I posted on the 1.2.3 thread.


Hi John,
Of course about the servo arm mount as depicted in my drawing at post #238 and #301 of the “onetwotwo” and now I remember well the schematic you indicated at the post #305.
Honestly I did not understood the real advantage of the large eccentric drum rotation and I should make a set up as in the pictures you added for better understanding !.
Thanks for remembering me.
Next I will introduce the 360° servo set up with a large drum diameter and deep throat and rubber/latex breaker to avoid string exit or jumping out.
Compared to the servo arm it requires much less power and the maneuvering speed is still quite acceptable.

The advantage of using an eccentric wheel is that it reduces the radius as you approach close hauled. This increases the effective power and also adds an increase in fine adjustment. At full out, the radius is increased, providing less power, but faster response.


Dear John,

I fully understand that if you are at close reach and release the sheet, the tension on it will be lesser and lesser until it reach zero when full out. But what about when you are running, with the full sail area almost perpendicular to the wind? If the boom is not resting on the shrouds, shouldn’t you get max tension on the sheet? Well, maybe a bit less because of the apparent wind but still.

Hi Claudio, I’m sure you already look at these but they might have enough power for what you need with normal voltage and take 7.4v so they’ll should accept lipo which are lighter then regular AA size battery.

1: Savox SV-0236MG this one has the highest power available at 40 Kg/cm for 7.4V at 0.17 speed.

2: Savox SV-0235MG this one is less powerful at 35 Kg/cm also at 7.4v but for the difference in price you may as well get the 236.

what I don’t know is if they have enough “debatement” for what you need.


Hi Gilbert,
The Savox SC1256TG was initially retained for the arm servo configuration. It is very noisy and finally decided to drop it.
The large loss of torque with the arm option suggest powerful servos that in turn consume more energy.
I’m more keen to adopt the drum servo and calculations demonstrate the validity of that choice.
Nothing is free as usual, since I need to modify the servo by adding an external potentiometer and loosing the warranty.
Two potentiometers of 5k in order for 1 turn (340°) and 3 turns.
Here below two possibles drum options among others.
Test will be carried out !


Typical configuration for a Servo Drum with external potentiometer :



I suspect someone has already asked but would not the RMG sailwinch do what you need. Fast, strong, noisy, expensive… but much like your drawing above

You miss the important ones : heavy and power consuming !!!


Potentiometers received and tested with Hitec HS-725BB and 2 gears 48t and 37mm OD
Only the Burns 3turns 5 k can be used. Single 340° does not work !
One full 360° rotation + 1/2 turn with the trim and ATV control full clockwise
Speed 1.8"/360° at 6volts .
To change number of Drum turns (max 2.2), the gears ratio can be changed. No loss of specified torque if servo axis is used !
Torque as function of drum radius.

While I was playing with servo and gears, I found in the old servo box this Hitec Note:

I did not pay attention at once.
Later I came back and start reading the folded part of the note.

At a certain point it written that the available kg force is reduced from the initial specification of 13.8kg.cm down to 5.67kg.
The drum radius is 1.9cm
My simple calculation about arm lever is : 13.8kg.cm/1.9 = 7.26kg.

Where is coming then the 5.67kg ?
I tried to play with sine/cosine and tangent and no answer so far except the one received from Hitec :

QUOTE - 13.8kg is measured at 1cm so when it is measured at 3.8cm they are saying the torque is 5.7kg… I don’t know what more of an explanation I can give? - UNQUOTE

Any better mathematical explanation for 5.67kg ?