IACC 120 now extends to South America!!! (ITA-45 Build Log)

Hello Everyone!

As I’ve already say on my introdcution post, this is the first RC sailboat I ever built, so please be patient with me! :wink: A few months back was browsing the web searching for some information regarding America’s Cup when I stumbled upon Renato’s Chiesa website. From that moment was love at first sight!
A few days later, talking to some friends at the local sailing club about those IACC120 sailboats I saw, came the idea of building our own boats, so two new hulls (ITA-45 & NZL-32) are being born right now in Argentina.
In my case, after looking for possible hulls I decided to start building Federico’s Nardome version of Luna Rossa ITA-45 which it seems to me, besides BlackMagic NZL-32 and Nippon Challenge JPN-41, the most atractive AC72’s hulls in the modern era of the America’s Cup (yes, I like the oldies!!).

It was time to work then, but before cutting a single piece of balsa, I’ve decided to first build a 3D model of the hull in order to analyze some aspects like true LWL according to real displacement, hull reinforcements, cockpit, possible bulb shapes, etc. Once done, I decided to go on with the male plug construction, so I can then get a the female mould.


  • Once I finish with the planking, should I just impregnate the hull with resin or would it be better to apply a thin cloth layer before start sanding? (I’ve used 3mm balsa for planking)

I’m attaching sompe pics of my job!


Please feel free to emit ANY comment… It’s good for me to know if I’m doing something wrong! :slight_smile:

Great work Andrés, welcome to the AC 120 class.

Having laser cut shadows makes life little easier and planking looks perfect !

Using 3 mm balsa it is general practice to coat inside of the plug with epoxy, to give the balsa strength so when start sanding the balsa will not bend between the shadows (creating hollows)

Next, lightly sand & fair the outside of the mould to remove major hollows & bumps then lay 80 gsm FBG over the outter side of the mould for final finish fairing.

I am not familiar with name Federico’s Nardome in regard to AC 120 design & plans, is it possible to post copy of the plans ?

You will have lot of fun with these boats & many people here will help when you need it.

Cheers Alan

HI Alan,
Happy to see a new start !!
This is the Federico link : http://www.velarc.it/index.php?option=com_frontpage&Itemid=1

Hi Andrés

Nice to see a new IACC120 build. Will enjoy following your progress.

Hmmm… Laser cut shadows… isn’t that cheating or doping or some kind of illegal practice? Though it looks great. :slight_smile: (just kidding)



I see your point, reinforcing just the interior side will make easier my job on the outside. Now I wonder if it’s necessary to use only Epoxy resin, or can I just use polyester resin? I know Epoxy is harder and much flexible… I’m just asking because I already have a polyester kit which expires in a two weeks, and perhaps I can use this instead buying an epoxy kit, which will take me few days just to get it (It’s all about time!!! Lol!).

Today I ended with planking, so besides having the interior reinforced, I was wondering which kind of mastic should I use in order to get all the holes filled on the exterior side. Is there any suggested mastic?

I’m attaching Federico Nardome plans and the hull 3D models I made (Rhinoceros 4.0 software is necessary to open the .3dm file).

Hi Andrés,

Thanks for the 3d images… looks very nice !

I have never used polyester resin but it should be ok to coat inside the mould with, can also use good coating of PVA as substitute, just be careful with whatever you use that it doesn’t seep through small gaps onto outer hull surface as sanding hard resin with balsa can be problematic with their different sanding cutting rates.

Ideally for fairing the outer mould surface, two part “light modelling mastic” (filler) is ideal as it sands very easily, car mastics are normally very hard and will cause same sanding problems as above with hard resin on balsa.

Depending on how fussy you want to be, you can cut some female shadows and use them to check hull shape as you go…extra work but if you making female mould for reproductions it’s worth the effort.

After you have faired the mould a good tip from Jim when laying FBG layer over the mould, warm up mould & resin to 25-30 C (read spec sheet) after laying-up the mould, put it in cooling down environment & the resin will suck into the balsa as it cools down & any air bubbles will shrink with cooling the temp. I find working with resins in late afternoon then leaving it overnight to go-off over night in cooling temp works very good.

For final fairing & finishing of the hull read Claudio build logs and you will see he sprays the hull with paint and then block sands the hull using the paint as a tracer to see bumps and hollows, repeat the tracer coat until you have nice even surface finish.

Short cut here is to use spray-on “filler primer” it’s little thicker than normal primer and cuts nicely with high grit wet & dry sand papers.

Cheers Alan


Thanks for your tips! I finally found some Epoxi resin, so that the interior reinforcement is done! Sadly, despite having covered the exterior I wasn’t able to avoid some drippings through the open holes in between planks. I assume I’ll have to be twice careful while sanding.
I will now start fairing the outer side of the hull; unfortunately couldn’t find any light model filler as you suggest so I’m considering using “gesso filler” which is used in the construction industry as a filler between gesso panels. Once I finish whit that I’ll then apply a light coat of car filler (which is based on polyester composite) before start painting the plug.
I didn’t mention, but the intention for the female plug comes whit the idea of building several hulls for me and 4 other guys at the local sailing club. I’ll be building these hulls and once they done, each one of us will be building their own rigging, sails, etc. It will be like an arms race! lol! New fleet is about to come!

I’m posting some pics of my job.

Great Stuff ! … a little extra elbow grease in sanding (my pet hate) but all worth it when you’re starting a fleet.

I’m on my 9th AC 120 build now, enjoy trying out different hull designs … my idea was the same to build fleet only thing missing is having interested local skippers, they are few and far between where I live :rolleyes:

Hi Guys!
I’ve been away for a few weeks cause I was on vacations, but it’s time to go on with this project… Hull plug is almost done; I’ve applied poliester filler and sanded like a slave.
I’ll be uploading some pics during the week!


Hi everyone!!
Well, here’s the situation… As you know, ladies and hobbies are not often a good combination, and ever since my IACC120 has been sleeping on the shelf. Fortunately, I’ve decided to came back to finish this (yeah, girl is now out of the equation lol)… Summer is coming quickly and want to enjoy it sailing both RC and real sacale boats! :slight_smile:

As far as my project goes, I’ve finished with hull sanding and took it for painting. They will be applying 3/4 coats of primer and sanding in between, and then a some final coat of polyurethane for final finish (hope to be able to upload some pics tomorrow). As I told before, I’m planning to make a female mold using “mold gelcoat” and epoxy putty.

Since the only thing I can do now is just wait for the paint job to be done, I’ll like to go on with appendages and here’s where a few doubts come to mind…

1st- Is there any place where to get bulb profiles? I’m planning to build it’s casting mould using a CNC machine so I’d like to get a shape as much accurate to real IACC 72 bulbs.

2nd- I’m also thinking into build a shorter keel and rudder kit in order to be used under low wind conditions so… what do you people think about that? A small amount of draft can be reduced that way, and since lighter wind requires soft movements (at least on big boats) having a small rudder may help without affecting performance (I’ll obviously have to respect CLR balance).

That’s all for the moment!


Hi there!

I’ve been playing around with both keel and bulb design, and as much as my knowledge goes these are my results. Hope to get some feedback from you guys before start milling it’s mold! :slight_smile:
Today I received hull plug after applying the first 3 coats of primer… tomorrow I’ll be sanding and taking some pics.


Last progress done…

Tomorrow will be sanding again and placing the base lip which will work as a top for the female mold…

Hi Andres,

Mould is looking great, well done :cool: I’ve been away for few weeks so little late responding to some of your questions.

  1. Regarding bulb profiles, here you can read some my input on the subject [u]here starting post #12[/u]

  2. I build-in a drop keel (30 mm) into my Blackmagic NZL-32 exactly for same reasons as your thinking (low wind conditions) can read [u]details here[/u] starting post #16

In this year’s Italian IACC 120 Championship a friend was racing BM NZL-32, wind was 3-4 knots in the morning and was expected to increase to 10 knots in the afternoon, so he decided to extending the keel fin to max of 420 mm in light wind.

On the water he & I both noticed the boat was considerably slower in light air with full keel draft, so took 30 mm out (takes about minute to change) and the boat was back at the front of the pack again, which proved to me that RC boats are very sensitive to wetted area, in light air.

  1. I have made about 20 different rudders using different profiles, aspects and shapes with varying areas and I have found IOM barn door to be the best so far. They are simple to make so you trail your own ideas.

Cheers Alan