@Claudio:
Re a sail trim control - there is a different (and perhaps simpler) method to what you have shown above that may be worth considering. Instead of having the trim on the jib, you have the trim on the mainsail.
It goes like this:
Jib sheet = standard, direct from winch / winch loop, through jib fairlead and finishes at the job boom
Mainsail sheet = from winch/winch loop, through mainsail fairlead, to PULLEY on mainsail boom (where the sheet would usually attach), along the mainsail boom to a PULLEY at the mast, down through deck near foot of mast and then to your trim servo (like a small arm-type winch)
Hope that makes sense
Maybe this picture will help…
First of all a huge thank to Claudio for the opportunity to be with him the launch of this project, after the long hours of designing and building not once but twice this proto-type I have to say when I saw it on the water for the first time … I was speechless !
Claudio was more interested in the hull performance than the sails and honestly the sails were so far from good settings, unfortunately the vang ran out of adjustment and the leech was too far open and then he had to contend with trying to sail the boat with independant Main and Jib servo on each stick while sharing the rudder control with the Jib control stick… which he had never tried before.
Driving to the lake I asked Claudio if he was excited and he said no …but I was ! After spending the prevouis evening going over the plans in detail with Claudio, on paper it was as technically as perfect as it could be in the design department.
Sail draft settings etc. were just gerry rigged to rough position but this boat is so dam fast I could not believe what I was looking at first, I had Jaguar in the water for 10 mins before ran into eletrical problems and running abreast of 123 upwind I could immediately see there is no way a AC 120 could keep up with this beast, a big statement from a 120 enthusiast that just came directly from the Italian Championship which I know I will get it in the neck for saying this, but I believe the 123 ís the fastest RC mono-hull on the water in the world !!!
Watch the video, going up wind it slides through the water so effortlessly with virtually no tuberlence or bow wave what so ever and the bow looks like it wants to lift all the time and when tacking she does not displace or push water she slides over it due to the shallow draft and all this with bad sail set-up, how much better can this boat be !?
After we got back to the studio and we looked at the video and Claudio was truly excited (not his normal self) and he kept looking at the video to check what he was looking at …The sails were not what they could be but the hull Claudio is PURE PERFECTION !!!
Thank You Alan !
It is true, this model have still a lot of potential other then the ones already appearing from the first entrance in the water. Very often during close hauled I let the boat to choose his road and eventually ready to intervene if necessary. The only interventions I made when I wanted to change direction, Some times I got confused with the triple joystick functions and two thumbs !
As you says, with a good sail setting, much more will be seen.
You mention to me that this boat will not need a flared bow since is good as it is, probably a reversed bow may reduce the bow wave drag .
Very impressive the absence of the typical “nose down” even with gust up to 17-18kt, not only, but some times was visible the “nose up”. Honestly I still do not know the reasons for.
To note that the sail surface was 77dm² and still performing well with that wind force.
Of course the hull is very well balanced between up-right and 25° tilt. The curve of areas prove it as well the LCF.
Is time for me to rest for a while and digest all what happen, although I’m thinking about another solution other then RMG for the two main reasons : price and weight.
Apparently the answer to my question, after consultation, is not coming from Servocity . What I need is only one 360° revolution with a torque of 26-29kg.cm (reduced to 5.7kg.cm with 90mm drum diameter). I check with Internet and You tube and found only 360 continuous rotation; such modification will imply the use of micro switches to stop turning and reversing the supply.
Any one may have a schematic to propose I will be glad to consider !
Was a fantastic experience with You Alan, many thanks to be there in Villepey !
The advantage I see is that there is less opportunity for the jib sheet to foul / snag / catch on anything, particularly in light wind conditions.
The method I proposed effectively moves end of the main sheet, whereas your method shortens the jib sheet in the middle of its run.
As you would no doubt be aware, in lighter conditions it can be hard to get the jib out as it is often wind-shaded by the mainsail - at least that is what I find.
Using your method, the jib sheet has to be pulled (by the jib) through a couple of eyes or blocks on the adjuster - more friction.
Your method would be fine in more windy conditions I believe.
However, I believe you have just been sailing in light conditions??
Thanks for your concern, been having a rough week or so and trying desperately to avoid the dreaded opiates…
Anyway, yes I’ve seen the film and it’s absolutely fantastic - I really am incredibly impressed (if a little jealous!) of the final outcome. From conception through to production and then finally ‘sea trials’ has been a fascinating process and to have finished with a yacht that performs to expectation is truly phenomenal.
I note from the film and both yours and Alan’s comments about what I can only term ‘thumb confusion’ with regards to having a sail sheeting and rudder on the same stick. I recall thinking at the time (when issues were first discussed) that it would perhaps be better to have all sheeting controls on one stick (ie, up & down for main and left & right for jib) then keeping the rudder entirely separate. There is an rc system available (name escapes me at the moment) which was initially designed for motor boats with a twin engine installation where on the left of the controller are a pair of sticks that only operate up/down with the right stick for rudder etc. Can’t help thinking that a set up like that would make control for 2 winches so much easier. Even if you were to go down the route of a single winch & trim servo I still think that sail control needs to be kept separate from rudder for ease of control. RC flyers out there would probably disagree as they routinely have throttle & rudder on one stick and do so successfully. Food for thought if nothing else…
I’m going to watch your film again and come back with more but in the meantime, huge congratualtions and many thanks for your kind thoughts.
I’m so glad to get news from your side. Thank You.
Don’t worry about future servo controls, since I will go back to the classic way as soon I will finish my calculations !
The basic idea of having used two servos was dictated by the fact that I did not trusted the Eurgle servos being capable to handle 77dm² of sail.
I decided thus to split the sail area, the Main with one servo and the Jib with the other, introducing some thumbs difficulties.
The film prove that I was right in assuming that the Eurgle with 8.15kg.cm at 4.8v and no load, was too weak for the Main with the 15/16kt of wind.
To note that the real kg force available on the sheet is much less 8.15/1.5 drum radius = 5.43kg .
According to the Kite formula , http://home.nordnet.fr/~amoreaux/cv/aerodynamique.htm :
F = 0.13 x S x V² x sin 20° (assumed angle of attack)
I get in theory for 15kt of wind : 0.13 x 0.77m² x 7.72²m/s x 0.93 = 5.54 kg force required without introducing the sheet friction.
Just read your last post and thought that 0.93 looked rather large for sin20 - double checked and you appear to have used the cosine, thus,
Sin20 = 0.34 & cosine20 = 0.94.
Therefore sheet load without friction (pretty major factor) should be 0.13 x 0.77 x 7.72 x 7.72 x 0.34 = 2.03 Kg force which of course the Eurgle should cope with. However, that rather annoying friction comes into play…!!
If I recall correctly there is a table of applicable factors which should give an idea of ‘system friction’ - I’ll see what I can remember and / or find.
Re controlling two winches on one stick:
I have combined two winches on one stick, not too bad once you sail it a bit. Best bet is to take all cenering off the stick - then top right can be sheeted out and bottom left can be sheeted in.
I have also done mainsail and genoa on one stick - mainsail is up/down and genoa is sheeted from side to side as you tack - the control stick finishes up using an inverted “y” pattern - once again - it gets easier once you have sailed it a bit…
Having a sailwinch and rudder on one stick would be really hard I would imagine…
Left joystick ( up/down) for the main winch - the left/right function not used
Right joystick (up/down) for the Jib winch - the left/right function with return to the center was for the rudder.
To do that I have also modified the transmitter joystick plugs positions.
Anyway this is the past history for the reasons explained above !
This Diagram is representing the wind force exerted on the 1.2.3. sail area of 77dm².
Two formula used are providing similar results.
…
In this Table are reported the servos that may be used :
…
Comparing the two tables, I can conclude that the HS-5980 used as an example with 5.33Kgforce, could go up to 15Kt, unless the sail area is reduced to allow higher wind speeds.
I’ve also just realised that the numbers we’re calculating for sheet load technically aren’t that, they’re the sail load. To calculate the sheet load we would need to calculate the mechanical advantage that the sheet attachment point to the boom has over the CofE of the sail. In principle, the sail loading which we can think of as acting through the CofE does so at a known distance from the sails’ point of rotation (for arguments sake, the luff). The sheet attacment point on the boom then provides the mechanical advantage. As an example, if CofE were to be say 5cm behind the luff and the attachment point for the sheet was 20cm behind the luff (and we’ll use your sail load of 5.54Kg) we’d have a mechanical advantage given by: 5 x 5.54kg = 20 x Ykg, re-arranging for Ykg = 1.385 Kg, once again well within the winch spec, thus leading again to the dreaded frictional components.
I hope that little lot makes sense - apologies if it doesn’t, I’ve succumbed to the opiates and am floating somewhere looking down on my keyboard!
Hi Row,
The diagrams above are most of the time referred to a flat orthogonal surface. I was reading some where that the same principle was applied to an hinged surface.
The Kite Formula introduce the sine of the angle and in my opinion is more realistic.
To consider also that running and close hauled are very different condition against the ‘apparent wind’
Of course some benefit are taken from the sheet attachment distance from hinge and this is a variable parameter from one boat to an another.
I don’t recall reading this aspect on books.
Would be interesting to verify all that with a jig set up
This is what could be test rig set up. I toke the dimensions of my Main boom including the CE and sheet hooking. The weight representing the exerted pressure should modified in accordance with the above diagrams :
…
Being a lever function, it shall be introduced the ratio between the two active distances like 162/225 = 0.72
That mean that the real force needed is 72% of what coming from the diagrams. In this case is a relative good new, unless I’m totally out !
I shall consult my teacher in mechanics anyhow !
Cheers
ClaudioD
I agree 100% with your test jig for the verification of the simple forces involved, but there is one very important aspect that isn’t addressed, namely the effect that ‘lift’ would have on the computed numbers. As far as I can ascertain, the equations used only hold true for a flat panel presented to the wind (with sine functions applied to compensate for the angle of attack) and makes no allowance for the lift generated. I’m guessing that this is fine when a yacht runs dead down wind, the sails then basically acting as wind catchers. However as the head of the yacht moves away from down wind the sails will obviously then start working as intended and generate lift. This factor is somewhat more difficult to calculate as the shape is almost infinately variable (it would be easier with a rigid wing sail).
From a practical perspective, if one took a yacht sailing in say, 10 knts of wind, when sailing dead down wind the sheet is fairly easy to adjust (some of which will result from the reduction in apparent wind). As that same yacht starts to head up until beating that same sheet adjustment requires far more effort, a proportion of which will of course be down to the increase in apparent wind, the balance from the generated lift. In this situation, even when taking into consideration the increase in apparent wind, the equations used (once the sine function has been applied) would indicate that less sheet force would be required when beating which is patently untrue - practical experience tells us this.
I guess in a round about sort of way all this asks the question ‘How useful is the 1/2 x (Roh) x V x V x S ?’ (where (Roh) is the air density for a given temperature, V is the wind speed in m/s and S is the sail area in M squared).
I know this is over complicating things, but it would be interesting(?) to know how to accurately predict the sheet loading for a given wind speed & angle of attack. I’m sure the designers of America’s Cup boats do all these calculations - why would they want to carry oversized sheeting with its attendent weight increases?
In the meantime, I think I’ll be having marmalade on my toast…!!
Possibly one could measure the servo speed for 60° as defined in the data sheets and the current absorption to verify the effort.
I need to think about, while waiting my teacher answer !!!
Cheers
Claudio
Why not buy a RMG Winch, and sit back and enjoy some SAILING !!.
SAILING is why we make model boats, worrying about how to achieve it, is very negative.
Buy the parts that will work - - no more worrying !
