I’m a new member at this site, but I have been watching the other IACC120 bulid threads and discussions for some time now.
A little bit of background info. Aprox. a year ago I started building a IACC120 with my father. We had talked about building a RC sailboat for a very long time, and by coincidence I found some IACC120 plans, by Renato on velarc.it. At that time i didn’t know about the class roules or this forum. Now the boat is almost finished, and i’m hooked! The first boat is built very strong and we forgot to take thikness of planking into account so the boat is big and heavy, therefore we call it “the fat lady”. It has been a great first time build, and i am really looking forward to putting it in the water and sail it. Now I will start thinking about the next project, a race ready IACC120 according to class rules.
Now back to the Title of this thread.
As i live in Denmark, I simply have to build the boat of the Scandinavian team Victory Challenge.
Here a link to a picture of the Victory Challenge boat
There is no plans for this boat to be found, so i desided to take up the challenge, and try to design it my self. I have been waching all the valuable infomation about boadt design posted in the ETNZ dual build thread and other threads, and i think i have an idea of what I have to do. I have run into a couple of problems though, which i hope some of you can help me with.
Regarding the displacement: Should I am at having a total displacement of 4500 cm3 (submerged volume of hull + fin+bulb+rudder) Most of the plans i have studied, have had a sligthly larger displacement like +100 cm3. Since the target weight of the boat is 4500g I would think that the total displacement should be 4500cm3.
When making the curve to find CC/CB is it only the submerged hull which should be considered or should I include fin, bulb and rudder cross-sections?
Attached a picture of my design so far, and one pic of the “fat lady”
Hi Anders & welcome to the forum, great job you have done on first attempt with the “fat lady”, one of our members Astute Composites IACC 120 build was based on Victory Challenge design, I’m not 100% sure but if you sent him PM through the forum he maybe able to help you.
Looking at your design graphic it looks resonably close to the ETNZ design, have you considered possibly using ETNZ hull design with SWE graphics ?
Thanks for your comments, and Claudio thanks allot for the plans I really apreciate it. It makes my life allot more easy. I think I will still draw the boat in my CAD programe (Autodesk Inventor), but according to your plans. I can see yours will look allot more like the real thing than my first attempt. Im of the generation of enginneers that cannot work without having it in the computer, it will propperly also help me when i have to build the mold for the deck.
Maybe I’m asking a big question now, but is not desired to have the longest possible LWL? I noticed on the plans that the LWL is “only” 960mm, woud it be an idea to modify the plans a littlebit to lengthen the LWL? I have always been told that the maximum boat speed and the waterline length is connected…
I will start by making my 3D model, and make the frames, acoording to Claudio’s nice plans, and see where it will take me.
I’m planning to finish “The Fat Lady” before starting on the new boat, or should i say boats. I thougt about building two similar boats, and arrange some small match race events for my friends, and see of sombody else would like to join in on the IACC120, so we could get a Danish devision going. That would be great!
actually the LWL is 970mm. Correct LWL & speed are connected by the simples formulas Critical speed Vc= 2.4 x Lwl if speed in knots
That’s teory ! Take two model boats with the same LwL lenght, one of 3.5kg and the other of 4.5kg with the same sail area, which will be faster ? That’s the practice !
The Rules allow to use a max LWL lenght of 1000mm. Two factors to be considered , eventual increase of wet surface and and change of the DSPL. You may play on the beam or on the rocker deept. Less deept will reduce lateral wave formation expecially during running and hence less friction…etc.
I have now finished transforming Claudio’s plans to my own 3D model. I used different screen shots to put in my sketches and making the sketches 99,999 % according to the plans. I then made a solid from the sketches and removed the volume above the waterline, to check the dispalsement. And check it out… actsactly 4030 cm3 like claudio’s plans.
I think it looks beatiful, I really like the shape of the boat.
Unfortunetly, i will have to wait a couple of weeks before sarting on the build, due to holidays in my hobby-shop. Untill then i will think about what meterials to get, and how I am going to do the different parts of the boat. I really like Jim’s lowered forestay attachment. I will also try to work out a sail plan, to wotk out mast position.
I have a question regarding rudder axle angles. My feeling would be that having the rudder axle in an angle and turning, would also cause the nose of the boat to dive, appart from turning. Is there anything to this theory, or is there also a possitive gain to have the rudder in an angle?
@ Claudio: I have made a Drawing A0 with all the frames ready to cut out and glue to the plywood. With your permission I could post the drawing as a PDF, for others to use?
Having the rudder axis at an angle moves the surface of the rudder aft…
I have found that then a smaller rudder can be used for less wetted surface and less weight.
Just a note - On the full sized sisters they have 360 degree rotating rudders so the rudder axis is at 90 degrees to the rocker so they can spin!
I use a much bigger main and a smaller jib, and the balance of the boat is perfect with this arrangement.
Just a note on the Waterline length… It always a trade off, but once at speed the water is ‘sucked’ up to the transom, using the whole overhang and extending the waterline. I feel that a longer overhang has a shallower angle and the water flows up and exits from the transom sooner than a steeper shorter overhang. I could be wrong, but that’s my observations on the matter!
the plans I developped were on Jim request, therefore and, for curtesy mater, Jim should agree also . For me it is OK.
I’m pleased to discover that I was manually calculating correctly the displacement ! hihihi !!
according to my knoledge and the AC Rules, indipendently of the LWL lenght, the overhang angle shall not be, in any case, be higher than 12.5° from the water line.
Finally i got a little time to make some progress on the project. Hopefully progress will be faster here in the winter time.
I have arranged the frames on the building board, beveled the edges and glued in the first planks. Now it is traight forward with planking.
The biggest problem right now is to find out how the rig and sail should look, so I can find out where to place the fin. Have been following the rig and sail thread, and will try to make my own configuration. propperly I will post it for comments when I have a plan ready.
The Fat Lady also had her maiden voyage. Pretty satified when I keep in mind that this is the first glassfiber boat, first rig and sails ever! In the video she is sailing in conditions I would call “No wind from changing directions” so not easy to se how the she performs.
Anders complimentrs for your work.
I’m a friend of Renato and he has been very happy seeing your video!
Just some suggestion:
-I noticed the mainmast very angled forward: has it been a case or is it necessary to balance the boat? With a 90° mainmast does the boat go to luff? It is not well balanced?
-The jib boom doesn’t have force. The jib boom moves upward in case of gusts. You have to increase the forestay and the backstay tension and/or increase the distance between te forward jib boom side and the jib boom pivot point. Obviously the mainsail curve will increase: you have to cut the luff mainsail with the new mainmast shape or you have to build a new mainsail.
Thank you for the advice. The video shows the actual maiden vouage, so actually no thoughs were put into mast angle, only to get the boat on the water. We tried to give it some more backstay tension, but as the mainsail was not cut according to the mast curve, so it totally f… up the main. Unfortunetly I haven’t been able to sail it again. I have been busy moving and traveling.
The boat is placed at my fathers house, so it is not so easy to go for a sail, which is also why I want to build my own boat(s), so I can go out when ever I feel like it. I am thinking about going on vacation i Italy next year for the cup, if I get the new boats up and running before then.
The hollidays gave me some time to advance with the project. I have now finished planking of the hull, and i am working on sailplans, rig layouts ect. I’m going for a big main sail with big head also.
I’m planing to continue the cocpit a little further towards the bow, and have the mast placed in cocpit height, it should allow for a better attack angle of the goose neck, and maybe a device to push back on the mast to straighten it, still thinking about that.
I’m haveing some problems in finding out the correct placement of the fin and bulb. I remember having read something about it, but gust can’t find it again. The dual build thread is very long, when you are looking for something specific. Can anyone point me in the right direction?
Attached some pictures of the actual progress and the digital progress.
I have now placed the fin and bulb correctly, and tried to position the mast so that the CE is 8,2% in front of the CLR, according to the plans.
It looks like I have gone a bit crazy with the mainsail size, the mast has to be placed way to far forward. And this is with a vertical mast. I gues it should be done with a backward angle of 1,5 deg, which moves the mast even further forward.
Propperly have to redo the sail plan. Second time is always faster…:lol: