ETNZ IACC120 Dual build thread

Other America's Cup Boats
81

Goose I always used this UHU Hart: http://www.uhu.de/_uk/indexx.html?main=/_uk/produkte/modell_kunststoff/hart.html

Developped for balsa revealed to be very good for Samba to

Cheers
Claudio

82

Thanks Claudio…

I saw a tube of UHU in one of your AC33 pictures and was surprised that they were still around as I remember using it when I was a kid.

Cheers

Goose

83

Claudio, I have question regarding IACC 120 class design.

I see the latest update of Luna Rossa design from you on the IACC site (I love that design) interestingly there are now 3 different versions now available:

  1. LR-A
    - LWL 960 mm (Short)
  • Rocker 44 mm
  • Beam 176 mm
  1. LR-B
  • LWL 995 mm
  • Rocker 44 mm
    - Beam 170 b[/b]
  1. LR-C
  • LWL 995 mm
    - Rocker 42 mm b[/b]
  • Beam 178 mm

I am interested why the 3 variations ?

This Class Rules aims to let sailing and racing RC Scale models that reproduces similar boats and reading the current AC 120 cup class rules for example LR-A with LWL of 960 mm the rules say “C.3.1 DIMENSIONS With the Boat floating in fresh waters LWL is 1000 mm +/- 3%” therefore making LR-A not eligable for racing ! have I understood this correctly ?

Cheers K1

84

Thank you very much K1,
You discovered a mistake or better a missing word ‘max’
The matter of facts should read :

LWL ‘Max’ 1000mm +/-3%…

The word ‘Max’ is missing in the English version, therefore the LWL has no limits specified except the Max Lenght.
Certanly the tollerance is a little too wide and may induce some confusion.

Why 3 designs ? Just to let the modeler a choice between 3 important parameters as LWL , Beam and hull Deept.
YThe Displacement remain constant, therefore the variation of one parameter do affect another one. “Nothing for nothing”

I will suppose that Matthias will introduce the missing word.

Thank you again
Claudio

85

Claudio, Thanks for that clarifaction, as I’m wanting to race competively with my new AC 120 I’m reading the rules detail to ensure I do get to the start, I don’t want to be knocked out before I start based on a minor technicality, which I could over look in construction.

Agree 100% with your “nothing for nothing”

Matthias, I will send you a PM as I need to also clarify AC 120 registration rules, I would like to sail under NZL designation, being a patriotic Kiwi :slight_smile: but living in Germany I’m unsure of the correct procedure to go through ?

I don’t want to branded as traitor by my fellow countrymen, like some our great big boat sailors :scared:

Cheers K1

86

Go Kiwi!!

87

Goose and K1, very cool project you have taken on here…you gonna have your hands full for a few months. There is a class down here “AC15” but I think no one down here sailing this class yet??.

Nautibouy, thankyou for link to Uv stabilised Epoxy clear, I have been trying to locate such a product for years…most UV stabilised epoxys have a murky finish. Used polyester Surfboard resin for years…with brilliant results, even out of the spray gun…but just could not get the strength needed with polyester…now if I can just find someone in NZ who stocks this 112 epoxy?.

Gary

88

Gary, SP also make a clear UV-stabilised epoxy, SP-115. Here’s a link:

http://www.ecfibreglasssupplies.co.uk/store/images/SP_115[1].pdf

There may be others.

I went for the System Three SB-112 because I got a good price on ebay; it seems like a good epoxy and is certainly very clear but it is medium viscosity and I think a lower viscosity, offered by SP-115, might be easier to work with.

Ray

89

I am one of those that sail the AC15 class here in NZL.
It is localized in Wellington only and there have been about 20 boats made by the registered builder as this class is very much a one design and is raced by the Wellington Radio Yacht Club.
There are a small number of boats in Florida with Larry Ludwig (three I believe )
It was developed from NZL 32 (winner of the cup in 1995) which is an older design now.
A few boats were built and sold by a commercial franchise for quite large sums ( NZ$14000.00 ) during the 2000 cup challenge in Auckland.
I do know that Mrs Bertarelli (Alinghi ) bought two for her husband Ernesto for his birthday. The freight bill alone back to Switzerland was NZ$ 8000.

I am watching with delight the flourishing of the IACC120 class.

Just a word of caution from my past experience. The “America`s Cup” words and logo are very jealously guarded and I would not wish to see anyone receive the formal letter from the logo guardians threatening to sue for a great deal of money if you do not desist from using either devise.
Just a "Heads Up "

90

IANHB
interesting your remark that is the second time I heard, the first was in France.

What about this ? : http://www.modelyacht.org/acclass.html

Cheers
Claudio

91

Hi Claudio…

I was playing around with the deck plan and noticed that the mast position on the model is around 72mm aft of the full size boat.

Is there a stability/speed/handling/model reason for that or am I wrong?

Cheers

Goose

92

What you may be seeing is due to the fact that materials don’t scale with area or volume. ie water density.

Also the model’s fin has a lot more area than the original as the chord is much wider.

John

93

Hi John…

Thanks for your answer.

I’m not trying to discount the design by any means, purely curious. Here is how I arrived at the question.

[see pic]

Thanks again

Goose :slight_smile:

94

Hi Goose,

Maybe a better answer is that both the fin and especially the rudder have a lot more area than the full sized. So the CLR is moved aft. So the sail plan (COE) also needs to move aft to maintain the balance.

John.

95

Sounds like a good explaination…

Cheers John…

Goose

96

Goose,

the AC120 is not a real “scale” model for the following reasons :

The real AC is long 24meters with a displacement is 24000kg and a sail area of 350m²
Now is if scale down at 1:20 you’ll get a model of :

long 2400cm /20 = 120cm
displacement 24000 /20x20x20 = 3000g
sail 350 / 20x20 = 87.5 dm²
bulb 20000kg / 20x20x20 = 2500g

Analysing above figures, you will se that the total weight shuld be 3000g and the bulb alone will be 2500g. The difference will let only 500g to build the complete boat !!! mission impossible !!!

This is why the AC120 have a displacement of 4500g minimum , a sail surface of 85dm² as maximum (never used) and a bulb/fin of 3000g , the remaning 1500g are used for the consruction.

Therefore being in practice a “different” model, also the sail plan and his CE is positioned as such to be between 7% and 13% ahead of the CLR.

Hope to have completed the previous assumptions.

Cheers
Claudio

97

Hi Claudio…

I knew it would only be a matter of time before you jumped in and explained it all… thanks!

The same thing occurs when I am scaling aircraft.

Now I am off to learn about CE’s and CLR’s…

Cheers! :zbeer:

Goose

98

Goose,

CE = Center of Efforts . This is the geometric center of the Sails and Sail Plan where conncetrate the Wind force.

CLR = Center of Lateral Resistance . This the counter part for the Hull/Fin/Bulb and Rudder

The two forces are opposing each other with a certain relative position (Advance) as such to produce a force able to move/push the full boat.

Most of the time in Bermuda rigged boat (main + jib), the CE is ahead of CLR of a percentage calculated on the LWL that is the lenght of the boat at water level.
The “advance” may change as function of the Sail Plan or the Backstay adjustment, Boat tilt, etc.

Generally, I fix the “advance” at 7% to 8% as an average and later adjusted as function of the boat performances. It is not rare to reach also 10% LWL or more.

Each boat has is own “adavance” that is dependent of various factors as Sail Plan, Hull shape, etc. therefore is not possible to establish the ideal position until the boat is in the water. The adjustment phase is called “TUNING”.

I beliewe it is sufficient for now, most can be learn from books as I did it.

A sketch may help :

Cheers
Claudio

99

HI goose,i saw on iacc120cup forum that they suggest you carbon tubes for the mast because they are lighter.i know a guy here in provice of Quebec that sells all kind of stuff to make kites and lines too ,my best rigging cord is .Laser pro gold 150lbs9spectra).and he has a lot of carbon tubes that can fit in each other. try that guy i got good service. www.legiteduhttp://www.legiteducerfvolant.cacerfvolant.ca. Ithink you can find interrestig products there. Gilles B

100

Excellent!

Thanks Claudio, thats a great start…

Goose