My last baby, very probably entering the construction asap !!
This model is a midlle way between an IOM and a class M, with a bit of AC and a look to the Maxi !!
This model is pretending to be the fastest of these models.

The hull is a monotype :

without hatch

and with removable hatch to get access to internal functions :

I let you knows more soon !


Very cool, Looking forward to seeing it in action!

Thanks John,

One sail Plan :

more details :


Hi Claudio

 That is a magnificent looking boat.  I see that you are not influenced by the current trend to use cheins, is there a reason for that or you just like clean smooth lines.

 Looks fast,


Hi Johnymac
thank for the appreciation.
this model is fully indipendent from any existing Rules and therefore I was free to design a model that is pretending to be the fastest of all models from 100cm up to 130cm lenght.

When comparing with the Class M :
Class M ranging from 4200g to 4400g and long fin and very tall mast and 72dm² sail area.
122 design is just lighter , around 4000g, is only 7cm shorter overall with less wet area, but using larger sail up to 78dm² with the advantage to use a shorter mast and a lower CE to compensate for the heeling moment. Light boat + larger sail + good righting moment = faster boat
When comparing with AC120 developed in Italy:
lighter displacement, longer lwl, less hull draft, less wave drag, similar sail area, longer fin and heavier bulb for better righting moment = faster boat
When comparing with IOM :
longer hull, better Vr, larger sail area, longer fin, higher bulb weight, similar displacement, thus same weight + larger sail + higher righting moment + longer lwl = faster boat.

Under preparation a chine hull design, but not according to te momentary fad, but a real full one.

IMO this model shall have the same hull for all models, remain a good range of freedom for all the remaining elements within the the limits as : fin lenght up to 48cm, bulb weight from 2.8kg to 3.0kg , mast lenght 1.80m maximum, sail area from 75dm² to 78dm², displacement 4.00kg minimum

Finally a rather slender hull for better upwind performances.


here below the 122 -Chine hull draft

some 3D views of Chine Hull for “onetwotwo”
This model is of very simple and cheaper solution with the use of balsa sheets and fiberglass.
It is supposed to be very fast with moderate winds, probably less performing with low wind since the wet are is a bit larger then the previous design.



I am not a designer, and not even a very good sailor. I was only wondering about chines. My main interest is in the looks of the boat newbe opinion, if it looks fast it will go fast. Personally I like your first plan much better I have not built a yacht yet but this one has caught my eye and my imagination I can see myself thinking more and more about giving it a try,

keep up your fine work,


Hi Johnymac,
chine hull have some merits, not only because is of simple and fast construction.
If you whish to know more, it is sufficient to digitize the words “chine, hull, design” on google/yahoo,etc. like here :
In a couple of days I will present the files containing the shadows drawings in scale 1:1 ready for printing via any Adobe Reader.


The calculated Wet Area of the two presented models :

onetwotwo round hull : hull 1616cm² + appendages 1146cm² = 2762 cm²
onetwotwo chine hull : hull 1687cm² + appendages 1146cm² = 2833 cm²

thus the chine hull have 71cm² more wet area = +2.5%
To note that the displacements are :
3724 cm3 for the round hull and
3679 cm3 for the chine hull , -1% volume

imo, the difference is probably not very large when compared with ac120 models that have similar wet area variations within round hulls.

Here the “onetwotwo” round hull Frame’s File Drawing in scale 1:1 ready for printing on A4 format :

The frames are drawn with squared edge along the deck line.
Up to the modeler to use as is or make a round edge after strip planking completion.
Strip planking with obeche/samba wood 3x6mm and/or 3.7mm
Frames with round edge and bowed deck as visible on 3D drawing, are not yet made.

I went back for some time searching for the lovest Wet Area and finally I stop with the present revision of the initial model.
Here the little brother “one.TO.eno” with round hull, just 1cm shorter but with 5.6% less wet area ! and 10.3% less from the chine hull !! is also the name of a Belgian piano/singer duo :�diath�que&menu1=6

Of 4 models, each one has is own peculiarity. The Wet Area being an important parameter, is not the only one that may be considered at model level, here below the comparison of the model’s frames :

I just added a new drawing “123” based upon vertical and horizontal stretching of the previous one “121”
Further reduction of wet area achieved, but the draft increased by 3mm while keeping the same main section surface .


This will be the building sequence for the hull/deck master mould allowing the direct external laminations for hull and deck. The supports and wedges will be removed after lamination process. The deck lamination will use the wedge provided by the hull. Wedges will be cut to allow assembly.
Similar wedges will be used if a female mould will be made !


We have been busy, haven’t we!!!

As a size it also fits in nicely between the CD43 & Marblehead - I’m liking it alot!!

This of course puts me in a dilemma, I was thinking of a CD43 next, but having seen these lines… At least the weather is warming up now so I’ll soon be thinking about the deck for ‘Enterprise’, and after that,ummmm, CD43? OneTwoTwo? AC120? Exactly how many yachts have you now designed & built since I started my ‘J’?

Keep up the fantastic work,



Hi Row,
there are 10cm difference in lenght !
The 43-900 was also the base for discussion about the use of a genua.

“122” -“121” and “123” are study variations on the same basic design. Recent evolution was dedicated to the reduction of the wet area.
I cant go further, except the introduction of the “wave piercing” concept. I’m not sure will bring a lot of speed advantage since the max speed is still too low to be very effective, but it cannot cause harm anyhow. Modelers are free to make their choices.

It is already planned for this summer to perform “comparative tests” with AC120 and class M in order to proof the potential of this design.
The idea is to render this model a “monotype” - drawings will be availables for self-construction.

If transport is not a problem to you, then this design could be the one.

I’m just finishing to draw the shadows that will allow the construction of the bowed deck.


After some days of thinking I came to decision for the following design approach :

The hull/deck assembly will be composed in three parts, hull, deck hatch , see shadows below:

Some 3D sketches to show the idea :

This approach will be comosed of two masters in preparation of eventual female mould.
The first model will be laminated directly.
Hope will be ok since is the first time that I will use this constructional method well knone btw in the Class M. After all the “123” is a sort of mini M with the rig of the ac120.


Justification about the shadows shape :

Smoothing the sheer deck corner, two advantages are obtained, the weight due to reduced volumetric aspects and reduced drag when heeling over 35°.
Further the deck with this integral shape will be more sturdy. No flat surfaces drawn except cockpit floor.


Separated shadows for Deck and Hull printed and ready for plywood bonding :

Frames cut and istalled on the mounting plane. Alignment check underway.
the hull appears rather slim !

Drawing updating and internnal setup + hull & deck frames !


Dear Claudio,

Very nice design and craft work, as usual! One detail intrigues me. Some shadows of the deck present step curves near the deck/hull line. Is it an easy task to curve the 3x6mm strip planking in order to mould and glue them properly on the shadows? Do you prepare the wood in some way previous to planking? And is it an easier task with your recomended obeche/samba insted of the more traditionnal balsa wood?