Vor70 & imoca

hi everyone,

i’m french, 29, and discovered rc yachts about 2 ago. I’ve allready build a small yacht that works very well ( 75cm long; drawings found on “racing sparrow.nz” )
I’m currently working ( slowly but surely ) on Claudio Diolaiti’s ALINGHI SUI 100 drawings.

And few days ago, i found 2 interesting drawings published by M. Nourry on Delftship. I’d like to build both of them at squale 1:20 and i have some question:

that drawings ( squale 1:1 ) show the LWL at 332mm for the 60ft and 406mm for the VOR70. I think that it must be higher, reduced to squale 1:20… Can’t be 16.6mm and 20.3mm. Not enough submerged bulk. Don’t you think ?

So it is necessary to modify the sections to adapt them at 1:20 ?
And if the projects are feasible, could somebody help me to find other details like ideal sail plan, bulb weight, etc.

hi again,

Just add two picture showing the curves of areas of both boats.

thank you all.

Hi Paulin,
welcome back.
The two plans are based on meters. The 60ft is some 18mt or little more and the VOR is some 21.5mt.
If you wish to scale it at 1:20 you should first check if the available displacement at that scale is adeguate to carry all the weights represented by the hul/deck , RIG , Radio Installation, Fin / Bulb /Rudder.

Rispectively, you will get the Open60 of 90cm and the VOR for 107.5cm.
Knowing the reduced drafts of these boats, I don’t beliewe possible the construction, unless is a static model.

To remember that for the 1:20 scale, the original displacement shall be divided by 8000 - scale to the power of 3 (20x20x20), and the surface (sail) by 400 - scale to the power of 2 (20x20)


hi Claudio,

thank for your interest.
concerning the scale, it’s exactly what i want: 90.14cm & 107.5, so it will be possible to compare the perfomances between ACC, Open60 & VOR70, each build at 1:20.

the original displacement are 8.83 tonnes (open60) & 14.58 tonnes (VOR70) so it must be divisible by 8000:

Open60: 8830/8000=1.10375 kg

VOR70: 14580/8000=1.8225 kg

i can calculate this but don’t understand the result… does it mean that the total weight of the models must be 1.1 kg for the Open60 and 1.8 kg for the VOR70 ( with bulb, servo, etc.) ?

concerning the sail: ROXY’s sail surface is 280 m2 (près) and 540 m2 (portant) mast height 26.5 m
FONCIA 300 m2 620 m2 28 m
no information yet concerning the Volvo Race

i have a dream ! that every kind of boat were sailing together in the same water, with the same rights…
there must be a solution !

waiting for more informations i send you the pictures of one of both hull i have done.

I saw your new drawings about ACC sport & ACC 1:30, they’re just great

thank you Claudio, hope you’ll find some solutions.


I went checking booth plans :

the Open60 will provide, once scale down to 1:20, only 1075 cm3 of displacement and the VOR only 1778 cm3
I strongly doubt any RC boat to be made with that volume 1075cm3 and lenght of 90cm .
For the VOR is also very critical, I assume you need more than 3000cm3.

The AC130 of 80cm I presented, need some 1360g for the construction including 800g for the bulb.


is correct what you have understood

“… does it mean that the total weight of the models must be 1.1 kg for the Open60 and 1.8 kg for the VOR70 ( with bulb, servo, etc.) ?..”

Yes 1100g and 1800g all included boat ready at the buoy for sailing !

Très bien pour les photos !


good morning Claudio & all,

stupid question ( must be ) : i thought about it last night : what about adding P.U. foam in the hull, down the water line ?
It could make it floating much more and create a gain of weight…( like a sail/surfboard made of stratified polystirene )

have a nice day

Good morning Paulin,
the foam inside do not modify the shape and volume of the existing hull that define the displacement will only adds weight even it is a small weight.
The foam used for the surf boards it serve to create a volume that do not exist yet.

hi again,

ok, no foam…

another idea: a longer fin would mean a lighter bulb. if the AC 1:30 ( 80 cm long, 1350 g overall ) needs a bulb of 800 g, the Open 60 1:20 ( 90.14 cm long ), with a longer fin could have a similar bulb, even lighter ?

my last idea: adding some surface, increasing the curve of each section under the LWL to increase the volume… ( didn’t manage to modify the picture but think you’ll understand )

my very last idea: give up…

but i can’t believe that nobody on earth ever thought about building an Open60 or VOR70 at scale 1:20 and found some solutions !!!

Certanily for a similar boat in lenght you may expect no much difference in the bulb.
Having said that, the bulb weight shoul represent , for a good stability, at least some 65/70 % of the total weight. In this case a boat of 1150g x 70% = 805g for the bulb, or 750 if at 65%.
The problen is what remains for the costruction, in facts 1150 - 750 = 400g this is what is available for the complete construction using the smaller bulb .
The complete construction comprises the : Hull & Deck, the Rig , the Radio/servos/battery, the Fin & Rudder.

Yes, you can modify the shapes of the frames to search for a bigger volume, but at the end you will get another boat that certainly will be different from the original.


PS: If you check my AC130 you will notice that even being shorter , the construction will weight some 560g. The design displacement is above 1400g.

A longher Fin will allow to use a smaller Bulb, within the same righting moment , but it will increase the Wet Surface increasing the resistance during reaching with low winds/speed.

Claudio, just take a look at:


a modeler site that shows Open 60 at 1:10 & 1:18 scale. those constructions are fully detailed ( so surely heavy ), close to reallity, even at 1:18 and it seams to sail well…

dispsplacement at 1:18 must be: 8830 kg / 5832 [ 181818 ] = 1.514 kg ( ONLY !!! )
i don’t understand how they do it, so i’ll find this way.

thank you for all

If you read the details of SODEBO 1/18 , you will discover that the total weight is 4.8kg. From the pictures is clear that the hull forms are modified.

so i ask again: How can they make sailng a boat having a displacement of ~ 1.5 kg, 2 kg max.( seeing the pictures showing the LWL painted aprox the same place than the drawings i got, even different at scale; or others 1.18 sailing on water ) made with an overall weight of 4.8 kg without being submerged up to the deck ?

concerning the modification of the hull form, it does not appear obvious ! some front sections are larger but not deeper in my opinion. Not enough to justify a displacement of 4.8 kg…

Whatever, each plan is a personnal interpretation ! no one is officialy patented by the IMOCA.

i shoud learn to use “CATIA” in order to find the best compromises…
an other solution might be working at 1:10 scale but i would need more space to work…

thank you again Claudio
it looks like you have been the only one interested in this project…

i’ll try to go further and will be back in a new thread entitled: “building an Open60 at 1:20 scale” or maybe not.

thank you all

If you do a search of this website, you will find some previous discussion regarding a large, semi-scale 1:10 class. Here in the U.S. we even have a manufacturer of scale size Harken blocks and other hardware.

thanks Dick ! i’ll check it.

but for instant the war is not over !!!

i took back the curves of areas and re-calculate the submerged volume and found… : 4310 cm3
this way ( Claudio’s way ) :

[18+38+55+68+ …09+03] = 862 cm2 ; 862*5= 4310 cm3 !!!


no the same as 1104 cm3

i’ll have a nice day, as all of you !

Hi Paulin,
I’m afraid that something don’t turn round.
Where coming from the 862 cm² ?
Where is coming from the factor of 5 ?

Just for comparaison , a class M that is long 129cm and generally the hull displacement is about 4000cm3 , the total immerged frames surface is in the order of 310cm²…therefore 310 x 12.9cm ( distance between frames) = 3999 cm3 !

Please check or explain !


horrible mistake !

i thought 862 cm2 was the total of immerged frames surface you can see on attached file in post #15, but didn’t reduce to scale or the wrong way…

5 in cm is the distance between frames at 1:20 ( 18 frames, 18 metres, 1 m =5 cm )

i found other drawings and will try to calculate the submerged volume. it looks larger than first…

hi everyone,

i took the new drawings and went back to my new bible: “déssiner son voilier” writen by Claudio.
i found the displacement calculation method and the new results are: 1458 cm3 for the submerged volume and 46.27 cm from section 0 for the CC.

it seems to be correct and sufficient to try the construction.

if it’s needed 1360 g for the construction of an AC 30 of 80 cm long, it must be possible to create an Open 60 of 90 cm long with a weight budget of 1458 g.

just drop the deck view showing the LWL and the CC. looks good…