Back to PICO design :
Checking the theoretical capacity to withstand the Wind Speed at 30° of heel.
Although having reduced the Main Luff height to 850mm, the LCE, the LD and Sail Area are still the critical parameters unless more weight is dedicated to the Bulb that imply a larger/deeper Hull and heavier model !
New technology for internal supports as well Lithium dry Cells and carbon hull/deck, may help to better distribute weights.
Under the presents conditions the boat cannot support more than 9knots of wind without increasing dangerously the Heeling Angle.
Claudio
A step forward for a wind of 12kt, the required bulb is of 582g. Added to the actual 330g of construction, we are above 900g for 500mm long boat.
Sail area was reduced to 1095cm² and keel increased to 240mm.
If some one whish to scale down a RG65 from 655mm to 500mm length, will be surprised !
Ideally a 500mm boat should weight 550g and the bulb 350g while the full construction shall be within 200g.
If the Footy was constructed with 132g, not excluded to make it with 200g !
Having never been at a race, is there anything that says you HAVE to race with an A suit of sails?
So you design your boat around a lower luff length, which would drop the COE (if I’m not mistaken) and mean that you could then have a shorter keelfin / lighter bulb.
Sort of like when they changed from ridiculously large displacement engines to smaller engines with better handling?
Andrew, the Nano provisional class rule allows 3 rigs.
Typically, the A rig is used until the wind makes handling the boat difficult…trouble tacking or broaching downwind, etc. Then the smaller B rig is used, then ultimately the C rig.
It is up to the designer to decide how large each rig should be based on expected local wind conditions for racing. For example, winds on ponds in the USA are typically lighter than those in the UK, so I might make rigs larger than my UK friends unless I intend to travel.
Andrew,
Is not a question to race or not, the point is that lowering the main sail it also lower the CE position and this is helping to increase the lateral stability. Better would be to increase also the Fin depth.
Cheers
I do have revisited the PICO design in order to reduce the construction weights as well checking the max Wind Speed that can be met up to an Heel angle of 30°.
My dear friend Pierre Raynaud indicated the Arm servo peculiarity and found out that it is more complicated than what I was use to.
Since Servos are one of the major contributors to the total weight, this analysis was directed to the servos optimization.
The Bulb is also a critical item.
I told myself that if the total achievable weight would stay below 550g and the bulb at 350g this would permit a ratio of >63% and providing a decent model for sailing.
Unfortunately this combination have others limitations concerning the max Wind Speed sustainable.
Both calculations are in pics below.
The construction remains again a week point since the total weight is above the design data with 580g and the max acceptable Wind Speed is limited to 4m/s equal to 7.7knots.
This limited performance is nevertheless achieved because the Sail Luff is of 750mm and lower CE.
IMO, larger Sail Area will impose larger Bulb and Boat weight.
If some one is capable to produce a full boat for less than 200g will be a good achievement although the acceptable Wind Speed will remain below the 5.0 m/s or 10 knots.
Deeper Fin would help !
this thread has some brilliant info.
Thanks for putting numbers in the servo picture - I never would have been able to figure out where to start looking at those equations 
I’ve got Delftship and freeship installed on PC’s now and all these numbers/coefficients are finally - slowly - making sense.
I had never realised that all these co-efficent numbers are ratio’s and not values as such (not a great maths brain by a long shot) but I can start to see the inter-relationships of them now.
Claudio - you have mentioned that the the M-class has the 70% ratio of bulb vs total weight and it would appear that it is a good benchmark to try achieve.
How did the M-class get that figure? Just trial and error over many years?
About servos and calculations there some variants as the ways a Servo Arm is used.
For a new model, the servo choice is part of the weights game where one like to have the larger power for wind speed and less weight as possible.
Hope the figure presented are of some help to understand what are the limitations, the first one being the construction weight against the ballast that can be compensated with hull beam and draft.
About benchmarks, the class M has funny story concerning the Sail Area, but this is part of the heritage history.
The Rules call for 0.5161m², but this specification is refers to the simple triangles composing the Main and Jib.
There are other formulas that define the additional surfaces and for a Rig A is not rare to get a real total surface of 7200cm².
Instead on the weight side, in modern Class M the displacement is averaged at 4.4kg and the bulb around 3.2kg, thus 3.2/4.4 = 72%. This give room of 1.2kg for the construction.
Good modelers can manage to reduce the construction weight to 4.35kg and some time even less, in this case : 3.2/4.35 = 73.5%. This is possible mainly because of the Carbon tissue, and modern Servos and Battery. I have seen a class M for 4.250kg. Was supposed to be manipulated with care !!
Excluding the RMG, in the past, the most common servo was the HS-725HB of Hitec (replaced by 785HB) that weighted 110g for 13kg.cm at 6.0V, today for 65g you get Servo Arm of 20/25kg.cm.
I can adds in the benchmark list the Class AC120 that compared to the Class M is 9cm shorter, but the Sail Area can go up to 8000cm. Extremely fast and stable model. Average Sail Area 7800cm².
Up to now I do believe that the Class M is a benchmark overall, but the IOM or the RG65 are also benchmarks within their respective dimensions.
Hope that ESTEREL"45" will be the New Benchmark ! heheh!!
Cheers
A design trial in line with what written before. Swing Rig used to keep simple, efficient and lighter as well.
DSPL 611g
Bulb 380g
Constr. 231g (to be of concern)
ratio 62.2%
Sail plan 1100cm² (could be increased to 1250cm²)
Main Luff 750mm
LWL shorten to 480mm
The Hull is not very wide and there is some margin to increase the Volume in case is required although the weight will increase.
Personally I would prefers to keep the total weight as low as possible but depend from the construction.
Claudio, are you sure you aren’t being too conservative? My Footy A rig (based on Claudio Vigada’s Easy Rig III) is 1910cm2. I’m sure won’t stand up in 12kts, but I don’t see why it would have to.
Not my fault if Bernoulli did not considered Footy in a protected environment !
My static calculations are simply based on the Bernoulli law application and, of course, conservative by definition.
see: https://www.theamya.org/sails/146_SailsPart2.pdf
A review of the static Footy sailing conditions with a bulb of about 300g and 1.9dm² of sail area, the calculations reveal that with a Wind of 2.5m/s the tilt = 30° and with 3.0m/s the tilt = 45°.
Tolerated +10% Wind Speed when CE below 50/60cm from water.
Here the PICO 1200 cm² Sail Plan
Swing Rig A
Main Luff 850mm
Jib at 22%
Claudio, I’ve never measured the wind speed for my Fooy, but your calculation seems to be in the ballpark.
In this game it is difficult to be more precise since a boat is not like a car driving on a solid element.
2 out of 3 elements cannot be scaled and their implications predominates more and more as the boat get smaller.
An interesting book: “The Forgotten Factor” of CA Marchaj
Here what I consider a pleasant sailing with smooth maneuvers with the AC100 and RG65 and 3 kt of wind and calm environment:
https://youtu.be/R4MM_z_q3aI
I think is time for me to go back to my Class M “1290”…
Speaking of car analogies (which is what I always use because I’m more comfortable with them) I had a penny drop yesterday.
I have been thinking of the sail plans as the “engine” of the boat.
bigger sailplan = more power.
Correct me if I’m not mistaken, but the wind is the engine, not the sailplan.
The sailplan would be the gear box.
WRT the Pico, If you have can give/upload the stations I’ll build it in CAD and upload the STL/OBJ files for anyone wanting to try print them.
Bill also kindly supplied me with his IGES file that I’ve been playing with. I’ve successfully converted it into an STL and with his blessing I can also upload that… I’ll post in the “New class” thread
Andrew, I’d appreciate your waiting just a bit. While I’m confident that my Nano will sail well, I’ve never been comfortable with releasing plans to the general public before they are fully tested on the water. There are a couple of them being built as we speak, so it shouldn’t be too long. Once some testing is done, and any resulting tweaks made, then I’ll make sure you get a new file that you can release it wherever you want.
Thanks…Bill
Of course:)
Sorry, I just get carried away lol.
Hi Andrews,
PICO is a difficult model that personally I will not build, since I prefer bigger models !!!
Free plan, in attachment see PDF files of PICO-1C.
Shadows are at scale 1:1.
My worries remains with the construction weight that is actually limited to 233g.
Servo Arm not useful unless positioned far away from LCB. Drum servo retained but the weight is 45g already.
Swing Rig retained since lighter.
Overweight will move up the floating line, may be still acceptable if limited to 1-2mm max since the LWL is of 480mm.
Cheers
Just elaborated the 3 swing rigs A, B and C. As said before the swing rig at this size level is lighter because Stays, Shrouds, Spreaders,Turnbuckles and supports are absent. For those more interested about Swing Rig see : Ivor Bittle website “the RC Racing Yacht Explained” ‘Chapter 10’ : http://www.ivorbittle.co.uk/