Having consulted the NANO Rules, I just tried to compare with a similar length model like the Micro Magic.
There are some data that may be difficult to cope with.
The NANO Sail Plan aspect ratio is rather high compared with the Micro Magic.
The Main Luff is 900mm against the 980mm of the total Micro Magic height
My preliminary calculations for the Nano shows a possible Sail Area of about 1700cm² against the 1450cm² of the MM, it can be less if both sails become narrower like the rigid sails of AC catamarans.
Similar righting moment of the MM can be obtained with a bulb of about 275g, but the height of the CE may requires more weight in the bulb to get similar stability against wind pressure.
No calculations made, is just a guess.
I wonder about stability !
No further comments!


Here below the comparative templates.

Claudio, I use a 350g bulb in my 500g Footys.

That was only a comparison when found out that the MM bulb is available as spare part and weight only 376g attached to a Fin of 134mm length. This may also justify a short mast !

Personally I would try about 525/550g bulb to obtain a total displacement of about 750g (ratio 70%) compared with the 860g of MM (ratio 47% which is very low).
Need to verify if the total construction can be obtained below 225g.

I went to check some parameters and got my personal idea.

It is obvious that when a boat is getting smaller, the uncompressed construction weights become the predominant factor.

Increasing balancing weight (bulb weight) to compensate the relatively high aspect ratio of the Sail Plan make things more complicate.

Ending up with an heavier model will not help to get acceptable performances.

Actually my Construction Budget is 340g, that’s includes Electronics, Rig1, Fin, Rudder, Hull-Deck, Supports. It may be larger !

Adding a bulb of 500g, the final boat will be 840g at the buoy.

Unfortunately the weight Ratio will be rather low : 500/840 =59.5% - (Class M >70%).

One may use a bulb of 600g and the Ratio will become : 600/940 = 63.8% that is better, but the boat will be heavier imposing a larger Sail Plan to get some sailing performances, etc.

The sail plan considered is 1350cm², larger plan possible, but lateral stability will be critical.

NANO, a difficult Model to build unless construction weights are smaller and mast height shorten.


While others talk about NANO, myself a tried to design a PICO for about 750g and 1350cm² of sails … hoping that she will not met too much wind !

Here the Chine Hull for PICO, although with more bulb weight and larger DSP, the ratio Bulb/Dspl is still below 65%

Recalling the Scale Factors when passing from one model to another. Volume rated at the cube of the scale and Surface rated at the square of the scale.

Scaling down from an RG65 of 1000g and 2250cm² of sails to a model of 500mm of length.

650 /500 = 1.3 scale ratio
the cube of 1.3x1.3x1.3 = 2.19 scale factor for the volume.
1000g : 2.19 = 456g displacement for a 500mm long model .
the square of 1.3x1.3 = 1.69 scale factor for sail plan surface
2250cm² : 1.69 = 1331cm²
Thus the 500mm long model should have a Displacement of 456g and a Sail Area of 1331cm².

Mission impossible !!

Calculations for the construction shows that the model will weight 330g without any bulb.
According to the scaling factor the bulb weight will be 456g – 330g = 126g, which is very very small.
The bulb weight can be increased but the Displacement will increase also and far above the 456g calculated above.
Assume to use a bulb of the same weight as for the construction : 330 + 330 = 660g.
This could lead to the total weight of the boat of 660g, but …330/660 = 52% to ensure a lateral stability.
A class M is around 72%
Better to stay above 65% and in case of Wind increase the Sail Surface shall be reduced.

The typical RG65 Main Luff length is: 1000mm : 1.3 = 769mm when scaled.
The typical RG65 Keel depth is: 300mm : 1.3 = 230mm when scaled

A model of 500mm length shouldl have the following parameters to ensure an acceptable minimum sailing capacity : weight Ratio : 550 : 880 = 62.5%

DSPL 880g
Bulb 550g
Construction 330 g
Main Luff 770mm max
Sail Plan 1350 cm² max
Keel depth 230 mm min

Just a question, how much does the box influences the micromagic dimesions? I mean, how much effort goes into the boat design, for a large company like graupner? where do they put the priorities, in a really good sailing performance or the best boat that can be shipped at a reasonable cost (i.e. no 2m single piece tapered CF mast), produced cheaply and easily assembled?

So basically the real question would be, is the micromagic a good comparison or benchmark for what would be a relatively “open” class?

That said, I do like the NANO idea, and please keep the discussion going …

On a side note, I really like your chined PICO Claudio … (I have a futinet footy), more info please?

Claudio -
thanks for doing the math on the NANO comparison. It saved me a bunch of work since I can’t find my notes of displacement and stability. They are around here somewhere - just couldn’t find them on first try. Wife says I need to clean up and organize. Who am I to say “no” to her "suggestions? [Big Smile]

Perhaps one of these days, I might get excited about the “FOOTY” class. In the meantime, I have a 2 meter catamaran that is calling my name and waiting for me to get the templates onto the building board ----before Christmas appears. “Oh My”

Thanks again for doing the math and results.

Hi Gio,
what do you mean by ‘box’ ?
MM has some limitations and is a toy for me, but most of them are compensated by the low ‘aspect ratio’ of the Sail Plan with the Main Luff of 760mm against 900 mm of the NANO.
The weight ratio do not play in favor for this model either if the Bulb is “apparently” weighting only 360g against a total weight of 860g. 41.8% is a very low ratio ! Far from 65% for an acceptable stability.
Is floating and cheap…what ask more !
Remember, waves and wind cannot be scaled.
I do not consider it a benchmark.
Benchmark for me means performances to be met, something to aim for !
NANO idea is born for a 3D printing, what will happen when exposed to 12kt of wind I do not know.
My posts were limited to explain what are for me the basic considerations for a stable boat.

Hi Dick,

there is no much calculations, just simple considerations when starting calculating a new model design, the Bernoulli law is left aside to avoid further complications.

The point, I probably missed, is that when the model is getting small, the materials and components are becoming a predominant percentage for the construction. To counteracts this aspect it is necessary to use larger bulb to met the stability limit.
Imagine a boat weighting 1000g and having 150g of bulb against another of 1000g and 650g of bulb !

OK Dick,

lets talk about a Footy for a moment and see what it is needed to sail ‘normally’.

Here below the ESTEREL 4 calculations.

It start with the general formula in blue that is composed of two parts, heeling force and righting force
Followed by the list of parameters and continuing with the proper calculations in Red, last data is the Bulb weight.

From the drawing:

Wind that day was blowing at >10kt.
The Hull Displacement of 529g
The Sail Area of 1150cm²
The Design Bulb of 303g
The ratio is not very high since 303 / 529 = 57.2% - could be far better if > 62/63%.

The drawing contains also the formula using the Bernoulli Law and Righting arms at 30° of heel, therefore the distance from CE to LCB and from LCB to Bulb CG are included.

The calculation shall provide at the end the BULB weight needed for the sailing conditions set above.

No difficult to apply the same simple calculations for different Sail Area and Wind Speed (always in m/s ²).

The results obtained with 5.5m/s Wind Speed is that the Bulb shall weight 401g while the design was fixing it at 303g.

Not possible to increase the Bulb Weight without sinking the boat. The amount of sinking (in mm) depends from the Water Plan surface.

Two possibilities: decrease the Sail Area or sailing with lower Wind Speed.

The original design is already critical since the Weight Ratio is only of 57.2%.

To increase performances, one should develop a larger Hull Displacement, not an easy task for a small boat like the Footy and his Box.

Assuming, nevertheless, a Footy design with a DSPL of 650g and 400g Bulb, the Ratio will be 61.5% .
Construction weight little bit more than 226g since larger Hull/Deck.

If Wind will increase above 12kt the boat will heels more…and “nose down” not very far away !

This simple formula do not account for sea waves and gust !

Certainly my ESTEREL 4 Footy is not the Queen of Seas, but among the others is not bad if sailing up to 8kt and not more !!!

This simple formula can be applied to any model !

My 3D-printed Footy weighs 482g ready to sail without rig.

The bulb weight is 350g of the 482 total.

My C rig is 24g, B is 34g, and A is 40g. The A rig mast height is 825mm.

With C rig, then, the ballast ratio is 69%, with B it’s 68%, and with A it’s 67%.

Though I haven’t built a Nano yet, I see no reason why similar results can’t be achieved with a boat in the 725-800g range.

So all together you managed to build the full Footy with 172g ! My Esterel 4 was 226g Can you provide the details of the construction weight budget as I did it ?
Where is the floating line ?

Happy to, Claudio.

Footy construction weights:

3D-printed hull with thinned epoxy wash inside…40g.
3D-printed fin with 2 internal carbon tubes…15g.
3D-printed rudder with carbon tube and aluminum tiller…8g.
servo cassette…24g.
3 AAA lithium batteries with plastic holder…32g.
carbon mast tube and aluminum rudder tube…5g?

subtotal construction weight…132g.
bulb from 12oz trolling sinker…350g.

total without rig 482g.

As you said, construction weights are critical in smaller boats. Being larger than a Footy doesn’t mean that it will be easier to build a Nano, though. On the contrary, I think it will be a bit more difficult because of the need for somewhat larger servos and the extra weight associated with reinforcing larger parts. That said, I think the Nano should perform well with a ballast ratio of 60%…a higher ratio could be an opportunity for a good builder to get an edge on the competition.

Sorry, by “box” I mean that it has to fit in a box that has the lowest shipping charges or that can be maximized inside a shipping container… Shipping and handling charges are taken into consideration when designing and producing a new product especially when it has a “niche” market like a RC boat …

Hi Gio,
Understood now what you mean. If not wrong, an Italian Editor offered an 100cm long RC Model called “Luna Rossa” where the ABS Hull was shipped in two parts. I suppose that the mast was also treated in the same way. Pretty sure that the shipping costs were predominant over the total not only because of the length.

Hi Bill,
at the buoy the total weight difference between the two models is 529 - 522 = 7g
Instead you managed to integrate an heavier bulb (+47g) “probably” because of a larger immersed volume !
It may be larger if your hull is also diagonal.
see pics

I don’t see how the immersed volume of our designs could be different, Claudio.

Displacement is displacement. If both boats float on their lines at the same weight, then they must displace the same volume.

As you indicated, the draft of my boat is deeper than yours, but what you didn’t have is the view that would show the narrower beam. So your boat has shallow draft/wider beam, mine has deep draft/narrower beam…the classic trade-off decision. But both have the same displacement. I didn’t, therefore, get the heavier bulb by increased immersed volume…I got it by reducing the construction weight compared to yours. If you reduced the construction weight of your boat to 132g, you could have the same bulb weight as mine, and your boat would float on the same line as it does now.

You gain some form stability from the wide beam, I get it from the heavier bulb. Which is more effective would need to be seen by match racing.

As said the overall difference at the buoy is only 7 grams, but the weights are differently distributed.
Since the Esterel Water Plan is 239cm², the 350g bulb could be used by accepting to increase the draft by 2mm and passing from 29mm to 31mm.
Of course the weight will increase to and the ratio will be 60%.