In the last year I received a lot of messages asking what I’m doing when drawing a plan, what sort of criteria I take into account, which software I use, etc.
There are no mysteries and every body can do the same.
This discussion is realated to the application of theoretical and experimental data.

The regatta winner need of course a good design boat and good thumbs.
A designer can be a good developper and poor performing skipper.
It is not necessary to have both capability at once.

The Formula 1 Pilots are not the Design Engineers. A Pilot become a winner when the Racing Car is also good.

A designer shall be, in any case, a good observer of what happen on the water !

As first I would propose to buy a couple of books related to Yacht Design.
These lectures will bring the basic knowledge needed to understand how a sailing boat behaves once in water.

The first thing I do consider is the environment where the Sailing Model will be used.
The major parameter is the dominant wind and the wind force.

In a simple way I can say that low wind conditions = low Prismatic Coefficient and vice versa with high wind conditions = high prismatic coefficient : PC

Reading the Books , the names as Reynolds and Froude are often appearing in the text and in the diagrams.
To knows more about a simple click on Google will help.

For better understanding the Froude number Fn is compared with another scale that reflect the Boat relative speed Vr.

The expected maximum speed that a sail boat can achieve is function of the Length of the Water Line.

Of course the speed is direct consequence of the wind strength.

Fn = 0.40 and/or Vr = 1.25 are the maximum limits that our Monohull models can reach.

Planning requires much higher speeds and higher wind conditions. Some says that the begin of planning wil start with a Vr = 1.4 and up. Stable planning regime can be obtained with Vr=2.0 and above

Watching the diagrams published in the books, it is easy to see that the major drawback for a sailing model is the total resistance encountered in the water when sailing.

The hull form is the second thing I look for, also because of the aesthetic point of view.
Vr = 0.8 is referring to low speed due to low windy conditions and a Prismatic Coefficient of 0.55/0.57 is justified, while at Vr=1.25 is reflecting high speed and of course high wind condition. In this case a Prismatic Coefficient of 0.59/060 is supposed to offer better performances.

Sail plans are not yet part of this discussion that remain close to the Hull Design.

Of course the same boat will be facing both conditions, with high and low wind conditions, therefore is up to the designer to select the most appropriate Prismatic Coefficient that will be function of the dominants weather conditions of that area where the model will be sailing.

The hull forms are playing an important role depending on the speed that the model is expected to achieve.
Personally I do have a preference for the Symmetric type Hull

The Diagram here under are complementing the text.

The tread will continue…


Thanks Claudio, great subject & looking forward to participating in a very interesting topic, I have enjoyed what little I’ve learnt from you so far … I’m still trying to translate my observations from the water… onto paper :smiley:

Thanks Claudio, I’ve been waiting for something like this.

Indeed this is a long story that started long time ago when in France non books where available in French language. Still today, nothing has changed.
Everybody knows how frustrating lacking knowledge of a foreign languages when travelling also as a simple tourist.
At that time I decided to write myself a book in French dedicated only to the “drawing aspects” of a Model.
Such a book, still does not exist also in English, as far as I know except an old book that do not exist anymore, as “Model Racing Yacht of Priest and Lewis” published in 1954. I have a copy that was evaluated at a auction some years ago for more then 300$.

Years later, under Italian friend’s pressure, I decided to translate the essential part the French Book.
The original book can be free downloaded from here: http://fourtas.free.fr/classem/claudio.htm
The short Italian version can be found here: http://www.nonsolovele.com/2013Tecniche.shtml as ‘Disegnare un modello di barca radiocommandata di Claudio Diolaiti’
The use of Google translator may help a bit in catching the essentials, although many error can be met!

With the maturity achieved with the use of CorelDraw 4 and 5 software’s since 1993, today is a simple game to draw a 3 views in less then 2 days despite critics often written in several forums.
CorelDraw ver. 5 is very difficult to find on the marked, but with close search on the web is still possible to get copies. This soft was initially developed for Windows 3.10. I remember well the day I purchased in LA the day was issued.
Corel Draw 5 replaced simply my Drawing desk, is a 2D drawing tool but plenty of features that make extremely easy to draw almost anything. At the beginning I used it for civilian architecture, including my house and houses of friends only later it became my preferred tool for Hull Drawings.
This was my first contact with a PC outside working office equipped with Apple machine!!!.

Hi Claudio -
I have Corel Draw v 9 - but I just haven’t spent the time to learn all of what it can do. Same with much of my software, as it seems we only learn what we want or need at the moment, and seldom go beyond or “push” the software beyond it’s intended purpose. I think this winter, I may try to devote and hour or two every (other) evening. Thank you for this thread - I am looking forward to reading it.

Regards, Dick

About Wind, there are several places on the web where to find Wind Data.
Here in France I use Wind Finder.
Below some screen shots of various sea sides like Nice in France, Brest north/west of France, Southampton.
Surprisingly Southampton, south of England, is much less windy then Nice or Toulouse that is an inland city in the south/west of France.
From the charts, the average speed in NICE is 8kts, in Toulouse is 9kts and in Southampton is 5kts.
Of course the coming week in Brest is rather windy !!!

This is the wind data collection method I use.


Other important graphics are represented by the LCB - longitudinal center of buoyancy vs Speed
and LCB vs Resistance…


With that graphic one can decide “where to put” the LCB as function of the wind speed represented by the Froude number.
Assuming a medium wind condition and speed of 0.35Fn, the designer should operate in order to fix the LCB at around -3.4% of LWL from the central frame vs stern.
Similarly for strong wind and high speed, the LCB should fall at -3.6% of LWL.

In general with my designs, I will be happy with an LCB sitting at -3.0% / -3.5% of LWL

Another importan issue is the LCB vs Resistance :


The LCB of -3.5% is presenting the lowest resistance with medium/high speed, Fn 0.35/0.40
but accepting a small increase it is also possible to select an LCB in the range of -2.5% and -3.5%.
giving thus a larger choice for the design, knowing anyhow the the sailing model will be performing better at one given wind speed only.
This of course is true for all conditions and the compromise is necessary.
Someone talks about “All Round” Model and I’m one of them, that means that an LCB of -3.0% will be a good compromise.

The 2 important parameters I consider, among others, are Prismatic Coefficient and LCB.
For the purpose of this discussion I will fix the Prismatic Coefficient at 0.59 and the LCB at -3.2%.

With that in mind, it is already possible to see that this model design will be developed for “Medium-High Wind”


Approaching more practical aspects.

Here below two outlines of water plans showing the difference between them with Low and High Prismatic Coef. .

With the Low Prismatic Coef. the immersed hull volumes are more concentrated to the central part of the surface, while for the High PC, the volumes are shifted to the xtremes of the water plan.
It is not necessary big curve variations to obtain substantial changes.

Basic Model specifications for a Class M :

LOA… 1289mm
LWL… 1270 mm
Beam… 200 mm
Draft/rocker… 45-46 mm
Hull Displacement… 3950 g
Appendix …450 g
Bulb… 3150 g
Ratio… 71.5 %
Construct… 1250 g
Prism. Coef… 0.59
LCB… -3.5%
Bow height … 110 mm


After the last post I went on my PC and started drawing the Class M according to the Specifications.
The first trial came out with a LCB of -4.5% and a PC of 0.584 and with 4161g displacement.
I have therefore shifted forward the Waterline Plan few mm and recalculated again the all and this last results are more in line with the specifications set below with : LCB -3.1% - PC 0.593 - Displacement 4139g .
Here the drawing:

watching the Curve of Area, the RED curve is appearing shifted right and this is sufficient to pass from -4.5% to 3.1%.
On the Water Plan the reported Red Curve is not very different from the black.
The rocker was also moved toward the bow some 15mm.
This is a new demonstration that within half day with Corel Draw 5 it is possible to draw a 3 views Model Plan.
Of course few details are missing as well the frames in scale 1:1.

Tomorrow I will try to explain the step by step work.


Some of the Corel Draw 5 desktop applications:


I have just finished some 30 screen shots taken during drawing process, this is the last. Tomorrow I will post the previous 29 images.
Ready for any questions.
Still missing the LCB identification inside the Curve of Areas with the “pendulum” method, will be for tomorrow !

BTW I wrote to Corel Corporation Canada asking where CorelDraw 5 can still be obtained.


This morning after printing on A4 sheet, I cut out the Curve of Areas (COA) and hung it on the wall with a needle.
3 observations:

a) The hull displacement is above the design specification and shall be reduced unless is accepted the hull lift from water of 1 or 2mm. Considering the vertical down component force of the wind exerted on the sail plan that is pushing the hull into the water, it may be wise decision to let the things as they are. Another way to reduce the hull displacement is to stretch the hull drawing from 200mm to 195mm or less and consequently also the water beam will be reduced.
b) The LCB is found at -4.6% instead of -3.5%. The Water Plan layout and /or the rocker outline should be “shifted” for about 10mm toward the Bow.
c) The Prismatic Coefficient is of 0.585 and if 0.59 is the final goal, then the rocker could be reduced from 43mm to 42mm. In principle this should help although this operation will reduce the overall displacement.

As the first attempt I’m satisfied. The Curve of Areas is meeting smoothly all dots representing the frame’s immerged surface. After all is a nice COA. One should remember that this curve is the ID card of the model.


Follows the screen shoots taken yesterday afternoon. Are 29 if I remember !
Another proof that a 3 views drawing, with all the essential design specifications, can be done in half day or less with Corel Draw 5 and me! hehehe !!

Here in attachment the series of screen shots taken during the design drawing with Corel Draw 5.
6 screen shoot per page and when necessary with short description.
I understand that without having in hand the CorelDraw software; will be not simple to catch the essentials and ‘tricks’ of the Menu manipulations.

Please do not hesitate to ask questions and I will try to answer!

• Screen shoot 1st Step:
In order to prepare the “working plan” I need to settle the "grid’ composed of 10 sections of 127.5mm wide.
The specifications call for an LWL of 1270mm.
The function of the Menu “transform” allow to repeat the number of slices. Selecting the object, the dimensions are shown in real time on top of the screen. Stretching the object the dimension indication is continuously updated
• Screen shoot 2nd Step:
This view shows the complete grid plan. Very often the magnetic guides are used to hold in place objects (any close figure is an object). Here a magnetic guide is already placed where I would like to place the water plan Central Line C/L.
• Screen shoot 3rd Step:
Using the “pencil tool” I have drawn the strait line in Red. The magnetic guides are obtained by using the mouse and left click and drag from the Top and lateral rulers. Double click on one guideline activate a menu window that allow cancelling vertical and horizontal lines.
14mm are added to the grid of 1270mm long to represent the soft Bumper. Total Hull length 1289mm
• Screen shoot 4th Step:
At the extreme are visible the ‘nodes’. Clicking on the last node to the left, a window will open to allow transforming the strait line into a Bezier line. The Bezier line can be manipulated as wanted by dragging with the mouse, acting on the extreme control points. Here the curve is representing the half of the water plan setting. Previously, with the ‘dimensions tool’ the width was set at 85mm for the water plan and 100mm for the deck plan (half plan)
• Screen shoot 5th Step:
With the ‘transform’ Menu under “effects” the curve is doubled upside-down. The full selection of the new object allows activating the “combine” function under “Arrange”. Once ‘combined’, the click on the extreme ‘nodes’ open a new window that allow to “close” the ‘node’. From this point onward the object is closed and can be coloured.
• Screen shoot 6th Step:
This figure represents the basic Water Plan. The Water plan is the first drawing I start with. Later, the outline can be modified if necessary to meet the required dimensions. Few tens of mm can produce substantial variations


• Screen shoot 7th Step:
This figure show the control points when the object is activated after the node “close” operation.
• Screen shoot 8th Step:
Similarly also the Deck outline is drawn. It is important to note that the maximum width is placed at about 67.5% of the LWL starting from frame ‘0’. Probably to far from frame ‘0’, it may influence the LCB position. This point will be discovered later. If would be the case, the outline curve could be “shifted” toward the Bow of some mm.
• Screen shoot 9th Step:
The screen shoots are very similar and represent the completion, for the time being, of the deck and water plan layouts
• Screen shoot 10th Step
Here I started drawing the Rocker line. Actually I fixed the lowest (draft) point at 43mm. Same principle depicted with the water line drawing. The Bezier line controlled with the Control Points. The maximum depth is positioned at 52% of LWL.
• Screen shoot 11th Step
The Hull side view is added in red. Actually the line from bow to stern is a strait line. During design finalisation this parameter will be adapted as wanted. Note that the Bow height is fixed to 110mm and the Stern height to 50mm. These parameters could be varied later since they do not represent a primary functional aspect rather then aesthetic.
• Screen shoot 12th Step
The two plans, vertical and horizontal, are settled. This operation generally is taking about ½ hour to fix it at the condition that the ideas are clear in mind. Off course the years of drawing experience, with all type of model class, make the job easier !!!

• Screen shoot 13th Step:
This is the start of the most interesting design issue. It consists according to the designer imagination and knowledge to define the outline of the Mainframe. Various considerations are taking place; the character of the hull form depends on this drawing. Between two points a lot of curves can be drawn, my self I chose that one as depicted in this close loop of the drawing.
• Screen shoot 14th Step:
This shoot show the general view of the drawing where I have also included the Curve of Areas Grid. This grid is a standard drawing that I have prepared and used for all Class M. Sizing change as per class of models.
More in details can be observed that I used the horizontal magnetic guides at the top and bottom of frame 6. A third magnetic guide is used for the LWL line
• Screen shoot 15th Step = Beam Ruler :
This drawing explains one of the “tricks” I use to specifically transfer the quotes of the frame width at deck and water plan level. This “personal tool” called “beam ruler” is first tailored with the hull width lines and then rotated by 90° and shifted to the frame detailed drawing in order to fix the frame width dimensions. Special care shall be taken to check the curve at the intersection with the LWL. This is the most important job during frame drawing operation.
• Screen shoot 16th Step:
The Beam ruler turned by 90°
• Screen shoot 17th Step:
The Beam Ruler is without the coloured surface only the outlines remain coloured in red and blue in order to make an easy identification : RED = Deck Plan and Blue = Water Plan
Magnetic guides are very useful during this phase. In this figure the frame 7 is considered and a close look is showing a small discrepancy at the LWL intersection. Better view on next image
• Screen shoot 18th Step:
Frame 7 need adjustment

• Screen shoot 19th Step:
Frame 7 is now OK.
Simply done with the use of mouse drag on Control Points of the Bezier line
• Screen shoot 20th Step:
All 6 frames are drawn; note that the magnetic guides are presently linked to the top and bottom of frame 10.
• Screen shoot 21st Step:
From this picture I actually start to prepare for the calculations of each surface areas of each frame.
Here again I have made another “trick” that consist in the preparation of a “stripe ruler” with fixed height = 5mm and width variable and tailored to the frame’s width as depicted in the next shoot
• Screen shoot 22nd Step:
I use 5mm spacer because it is easy for me to work on half frames and because of the actual scale 5mm = 1cm.
Different scale and spacers could be used, but the one I selected it give me directly the Frame’s surface sum as depicted in the next shoot…
• Screen shoot 23rd Step:
The Main Frame (6) surface area is 56.07 cm²
• Screen shoot 24th Step:
All the frames surfaces from 6 to 10 are reported on the Curve of Areas grid. Interesting the non one frame is outgoing from the curve, demonstrating that all frames are pertaining to the same ‘family’. Of course this is the “secret” when playing with the Bezier curves and good trained observation eye !!

This post conclude my explanation on the method I use in 2 half days to draw a Model Hull.
The time used was much longer the usual since was necessary to prepare the various screen shoots and writing text of this tread.
The Second day could be dedicated to the servos setup and Sail Plan Drawing fixing the elements needed for tuninig.

• Screen shoot 25th Step:
In this shoot is noted that the frame 6 layout is doubled and reverse shifted to the bow side.
The frame 6 is used as reference when drawing the frame 5. Actually, as all before, each subsequent frame is the result of the previous frame stretched in height and width using the magnetic guidelines and the Beam Ruler.
The dual stretching function will maintain the “character “ of the subsequent frame versus the previous as such that the full frames set will pertain to the same family inside the horizontal and vertical plans layout defined at priori. Appears complicated with words but very simple in doing it
• Screen shoot 26th Step:
Frame 5 (in blue) once stretched it become perfect and meeting exactly the intersections at deck level and most important at LWL level.
• Screen shoot 27th Step:
Overall view at this point on time
• Screen shoot 28th Step:
Progressing with the other frames drawing. One could appreciate the homogeneous forms !
• Screen shoot 29th Step:
All the frames drawn and red dots pointed on the Curve of Areas. The sum of all calculated frame surfaces give as result: 328.53 cm².
The Hull volume will be: 328.53 x 12.75cm (frame distance) = 4188cm3 or 4188g of fresh water.
The Main Frame surface of 56.07cm² x 127.5cm (full LWL) = 7148cm3

The Prismatic Coefficient will be : 4188 / 7148 = 0.585
• Screen shoot 30th Step:
This shot is the summary of all the drawing work. Some refinements are needed to match the specifications with very small variations on the LWL plan outline and /or Rocker curve.
The conclusion will consist in transforming the Frames into scale 1:1 ready for Print. Another ½ day work.

Finally all the work presented above can be carried out in ½ day.



I’m away two days & class is out already :slight_smile: great work Claudio !

Need to catch-up on reading whole thread but have question on screen shot #10: You show maximum hull draft shown at 52% of LWL, any particular reason for 52% ?

@Dick I’ve tried Corel 5 & 5X then 6 onwards and without doubt the original version 5 is the most intuitive version but it is very hard to find on the net.

Cheers Alan