Hi Alan,
I was sure that the building quality is there, but I’m afraid that a 120cm boat of 8kg is enormous and certanly not fast as an AC120 or even an AC100 that’s much shorter without taking into account my last design subject of this tread. Imagine that even a Class M of 129cm is much much lighter and stable. OK very nice for what it represent but certainly not a racing beast as we are use to deal.
Sprinta RC may gain some performances substituting the Fin / Bulb set but this is another story. BTW is it easy to remove the fin from the fin box, if any ?
Cheers
ClaudioD
Hi Claudio, yes your right it’s not a 120 or M-Class racing boat, but it is a well established class in Germany and growing, it’s the fun of sailing and the skill that goes with this boat that makes it attractive & serious boat at a different level to fully designed racing boats.
We spoke about the boat righting moment quite a bit as it’s C.G is very close to LWL which makes it sensitive in moderate to heavy airs as you point out, the keel fin (4 kg) is removable with keel bolt and they are thinking of adding a spacer onto of the keel fin head to lower C.G, the rudder fin is 1 kg cast lead as well, total 5 kg below water line but it’s C.G is too high compared to our full racing specs.
For heavier air sailing can reef down the main (2 reefs positions available in the main) which helps but reduces available sail area and maintain respectable righting moment, further they have two movable ballast weights (approx 1 kg each) which they use in heavy air, one at stern (in cockpit area) and other aft of the mast to help stabilise the boat.
Profile of of the fins looks (not measured) little too thick for racing purposes, guessing the keel fin is in the area of 15-20 mm thick, my immediate thinking was to cast another keel fin and move rudder weight into the keel, narrow the profile and lengthen the keel to lower C.G, this would improve boats righting moment out of sight in my opinion and maybe help eliminate the need for extra movable ballast inside the hull, Hannas may consider trying this, not quite sure.
Testing is required and see how changes in fins will affect boats CLR/CE relationship and of course helm balance, noted the mast sits on the deck without any step so need to be carefully with calculations in this area.
Cheers Alan
Hey, slow down ! This is not a racing boat as Marblehead, IOM or RG65 !
She’s a true scale model boat. Compare the photos of one of the “big” boats and the model, you’ll see how close all details are respected, apart railing (however, there are places to set it, if you want) and spinnaker.
Christian insists to maintain this scale aspect as closest as possible, he even sends me an aluminum mast head when I’d a problem with mine and spoken from build one using CF!
The jib is expected from many times, but I never see it. I think it will not be a self-tacking, but will use the sheet and lateral travellers of the genoa.
I forgot, the sails are made by the same sailmaker as the original ones.
I fully agree with you Alan,
SprintaRc appears to be an excellent monotype. In this case being all the boats the same, the pure speed performance is not a paramount importance. The plaisure is certainly great and the skipper skill is dedicated to the trimming and tumbs.
For play and relax I would like to have one !
Obviously as designer, the SprintaRC do not offer margin to play .
The fin fixation is rather delicate if I look at this picture , all 4kg are keept by a long copper or S/S rod, the thing get worst if one would integrate the rudder weight and use a longer fin.
I wonder if mechanically the rod will support the bending stress.
Having said that, actually we have made quite a progress toward the use of a genoa, as such that I’m already thinking to develop the same for the RG65 class.
The genoa per se is not bringhing additional performances except with very low wind where a 30g/m² tissue can be used.
The Genoa add charm a nice looking anyhow once sailing .
The mast is using the best profile available against drag. This should be used also on the AC120 even still heavy compared to profiled carbon tubes.
Personally I will go back to try to improve my design, actually what is bother me is the friction around the shrouds, therefore I’m thinking to add some “controlled slack” .
One of the pictures below show the solution adopted around the turnbuckles.
By the way in spite of the nice design, I do not like the ones used on the Sprinta unless they are fasten in some way to avoid accidental exit.
Anyhow was a very good argument to talk about, we will see what happen now !
Ceers
ClaudioD
Claudio,
Instead of controlled slack in the genoa circuit, what about modifying the turnbuckles to incorpoate bearings top and bottom so that those conical shaped covers would spin easily? The slack would only really assist when head to wind - as soon as there’s any drive in the sails the friction would still be there all be it somewhat reduced.
As I’ve stated elseware, I don’t possess the skills at the moment to produce diagrams like yours but hopefully what I’ve said is reasonably self explanatory…
Regards,
Row
Hi Alan,
I give a detailed answer of genoa system that I utilize on my AC/10 on this post http://www.rcsailing.net/forum1/showthread.php?5837-Genoa-on-IACC-120&p=60820#post60820 because I think that is a more appropriated topic to speak about Genoa on AC models
At the end of message I wrote this:
P.s. a similar system utilizing nr 2 (+1 optionally 1) digital arm servo (quite 150 grams totally) could be well used on one AC120 boat without problems. Anyway a normal jib boom could work well for competition use. My AC/10 didn’t gain nothing by utilizing genoa. The only advantage is during cicling utilizing genoa to improve quick and controlled movements of the boat
So you could do a similar thing alsoin the limit of AC120 Rule.
If you don’t want/can to utilize 2 servo arm only for genoa, you could utilize a RMG 280DL for the genoa movement left to right + trimming with proportional and fine regulation.
The travel and the power for the AC120 is sufficient
The barber to regulate genoa leech could be connected to the main sail servo arm (or winch) that at the end of the travel will close/regulate completely the main sail and the channel between genoa and main sail.
Naturally this need a perfect set up on land before navigation butit is the same problem for a normal jib.
In competition, I’ll repeat, I don’t think that coul be give any advantages but could be very beautiful to see
Could be that I’ll be in Mirabilandia for AC120 final match with my Urca AC/10 so you’ll se directly my boat and her Genoa and you’d touch and also sail with mine boat:D
Bye
see also http://www.progetto-urca.com/urca/Eventi/modelexpo2011/URCA_vasca/index.htm
Thank you very much ClaudioV for the opening of a dedicated tread to genoa applications.
I would like to recall to all that this is a tread dedicated to the 43-900 model as recalled by the title.
Probably was my fault opening the possible considerations about the use of a genoa after having observed the Sprinta RC performances.
A would therefore appreciate for the future discussions on " the genoa" be used the dedicated tread open by Kiwi .
Here I will continue, with your permission, describing the ‘build log’ of the 43-900 .
Obviously, with the progress of my project, it is not escluded that the genoa argument will be touched again in the constructional frame as integral part of the ‘build log’ if so I decide to use it.
Tank for your understandings
ClaudioD
No problem,
If you take a look of my message, I put this link
http://www.rcsailing.net/forum1/showthread.php?5837-Genoa-on-IACC-120&p=60820#post60820
that is the old (not a new) topic where it was speaking about genoa on AC models
bye
The 43-900 “build log” continue !
Here the mounting bench, tomorrow I will cuts the inner parts of the shadows …
ClaudioD
I resume the preparatory work done so far.
After alignement of all shadows, will start the usual planking with 5x3 mm obeche/samba strips.
ClaudioD
Finally a tool that I was searching for long time ! Now no more limits to my fairleads !
ClaudioD
After watching some images and the Vortex 60 videos, I was thinking about what may be hidden below the SC4 servo cover.
My immagination come up with the sketchs below.
With that, I do not intend to open a discussion that is now taking place somewhere else. This it is only for curiosity about a servo that is not existing anymore !!
In case I would like to make a “selfmade vintage servo” , the pictures are an highlight of what I could do. Obviously the rope may wear out, but it si not escluded to have some spares. I like the ball-chain and eventually the climbing frame approach !
The scale dimensions are the ones compatible with a Eurgle 10Y servo with 3.5 revolutions in 2.6 second at 7.2 V. (frictions and loads excluded) .
Cheers
ClaudioD
Hi Claudio -
take a look at this link (MicroMark) as they probably have some stuff you could use or want. It “looks” like they ship outside of US and Canada, but if they don’t ship international - AND if you are purchasing smaller items (not lathe or mill) you can ship to me and I will resend to you declaring as a “gift” so there should be no tariff/import duties.
Have done this for a few rc sailing friends in the U.K. and can provide name/reference to check out if you need something and want to try my forwarding if they won’t ship direct.
Regards, Dick
Thans a lot Dick, very kind of you, I will remeber !
Cheers
ClaudioD
PS:
43-900 aligned !
I managed to modify the initial study about rope-eater to get it smaller, obviously need to be made before telling anything. The main drive wheel as the free running rollers are equipedd with rubber bands.
The rope is supposed to be squeezed . The 3 rollers shall increase the friction to stop the rope when the servo is at rest. It may be a crazy idea but I will find a way to make one.
ClaudioD
Hi Claudio, now that is simplicity at it’s best 
…looking forward to seeing the test results
Cheers Alan
Hi Alan,
I was remembering a little toy selfmade when I was a child. It consisted to let the box acting as a descending lift. The movement could be stop by “magic” ! It was sufficient to pull the string a little and the box was stop, with a slight release of the string tension, the box continue to go down. The hart of the game was a simple spike glued inside the closed box and with a small offset from the strait string position. Pulling the string the friction with the spike increased sufficiently to stop the box going down !
The principle of the simple toy is actually considered for the above rope-eater.
Ciao
ClaudioD
PS : the 43-900 build continue !
Also similar to window shades where a sideways pull allows up or down movement. Another side pull allows shades to “lock”
I only remember seeing one Vortex “string eater” winch… From what I remember, it had two output gears (above deck, in a flat plastic housing) that were not quite in mesh… One was driven (through a gear train and motor, below deck) and the other was freewheeling… The string was compressed between the two gears and hence came in through one side and was spit out the other… It was quite a large braided Dacron, about 1/16" in diameter or even a bit larger… Once it had passed through the winch, it turned into a flattened ribbon with teeth marks on both sides… It was then nearly 1/8" wide (tall) and about 1/32" thick…
In order to prevent damage to the yacht, sails, motor, fittings, etc… the winch simply “stalled out” and part of the wiring harness to the motor consisted of a length of Ni-Chrome wire inside a heat resistant shield… That wire heated up when the winch stalled and it’s resistance increased… reducing the motor torque and limiting the current… This prevented the motor from burning out while you decided that the sails were in about as far as they could go and let go of the stick… The winch was not proportional… It simply ran when you moved the spring-loaded RH stick sideways… stick left to sheet in on the port side… stick right to sheet in on the starboard side (IIRC)…
HTHs…
Bob