The dimensions are definitively fixed as 50"/800in² to be compatible with “Vintage” VM Rules and as discussed in the previous pages.
It can be considered also an independent class by inverting the identification as : “800/50” , where similar models derived from America Cup yachts like J Class and 2Metres, could race together including multiple Jib and Genoa.
From what you select I can retains only the models that pertain to the presented list :
Endeavour II
Intrepid
Constellation
American Eagle
There were model classes based on the full-size rules in the 1920s and through the 40s: 6 meter, MYRAA class (based on Universal rule) and R Class. The problem with all of these rating rules (which force designers to trade sail area against other parameters such as LWL and draft) is that you have to have a tank in which to float the boat for measurement. Historically, the successful model classes have been those that could be measured “dry.”
This is one of the reasons I prefer to stay with the Marblehead Vintage Rules to avoid LWL measurement that often is source of disputes and funny objections like the surface tension meniscus size.
The work is progressing from yesterday. The main aspect is the Sail Plan reduction to 800in² from the scaled 1130in².
The original Sail Plan and recurved Mast is in the attachment picture
Hi “all”
I did not vote for the Australia II, but acknowledge that it looks great Mr. Claudio design, as in all his works.
Congratulations, and greetings to all present.
Hi Alberto, tanks a lot.
This is only the preliminary work far to be ended.
Next will be the Shadows - Hull lines correlation and fairing.
Volumes/DSPL calculations and Curve of Area, LCB.
Shadows drawings to 1:1 scale.
Cheers
ClaudioD
This is why I have chosen the Australia II as bench test. The small keel is magnifying the problem. Probably need to be filled totally with lead and producing a CG close to the Waterline unless the ballast ratio is radically increased to maintain a reasonable righting moment.
All this exercise is new to me. The real question is to find an equilibrium of weight distribution as such that the water line remain the same.
This feature will be the cross checked with another other model offering more keel volume. The basic final idea is to have similar righting moments.
The 52% is probably not exact but much depend on the hull/rig construction not yet evaluated, nevertheless I can make an assumption,
as an example, where only 1.7kg will be accounted for Hull, Rig and Electronics, the total weight of 6.3kg will authorize therefore a ballast of 6.3 - 1.7 = 4.6kg instead of 3.3kg.
The ratio in this case will jump to 73%, but do not tell me yet where the CG is located.
It is also important to find a “container/location” capable to hold 4.6kg, and bearing in mind that increasing the volume underwater will produce a lift and shortening the LWL…
The Keel sketch shown above exhibit already some limitations therefore adding another 1.3kg = 123cm3 will impose another keel form design.
The VM Rule accept a Draft up to 12inches ( 304cm).
I do not desire to modify radically the Australia II keel, but the calculations will dictate the way.
I went back to the Keel volume calculation and found out that I forgot in the previous calculation the scale factor of 2.
As a matter of fact, the actual Keel volume is 628cm3 trimmer excluded. See updated drawing above post 125.
Assuming the need of 4.5kg Ballast equal to 71% ratio, the volume will be 428cm3.
There are comfortable margins for improvement for the righting moment, but I need to check with models where I’m more familiar like Enterprise, American Eagle.
Cheers
Claudio
The option depicted to fix the ballast is an example. Modelers are free to choose other solutions what ever they like.
Treaded rod are integrated and bonded with ballast lead. The rods/ballast assembly, including the Trimmer, is sliding inside brass/carbon tubes supported by partial shadows.
Looks nice Claudio, just small point, what is the volume of the cockpit ? being closed the water trapped there may influence boat balance, just a thought
Hi Claudio, great work as always & thank you for all the effort in sharing the Aussie II design with us all, I’m sure their will be lot of people enjoying your work on the water.
Now I have a the dilemma of trying to decide which one to tackle first, Aussie II or J-Class Enterprise
100% agree with Alan, absolutely fabulous work Claudio! I often wonder just how many of your designs are now sailing / being built around the world…
Alan - Re your dilemma, Aussie II or Enterprise? For me it’s a no-brainer - you have a fleet of ‘modern’ racing yachts, I think now’s the time to start at the other end of the historical divide, so go with ‘Enterprise’. As you work forward from her & back from the AC120’s, eventually your fleet will encompass Australia II. Somewhere in the middle you should also acquire ‘Enterprise’ of 1970…!! I reckon that little lot should keep you out of trouble for the foreseeable future!
Tank you Alan and Row,
The Australia II work is not yet finished.
The Files will be updated with the keel detailed drawings (shadows in scale 1:1) for nominal keel and deep keel.
Static calculations of the righting moments will be added in order to compare the two keel options.
The nominal Sail Plan with the curved Mast will be added too. I have in mind two mast constructions options with aluminum bent tube and with wood sandwich.
About J Class,
when I decided to draw the Enterprise was simply due to the fact that this boat was the First Winner of the New JClass in the America Cup.
Next on the table will be the 12Metres Columbia, because IMO is the most elegant Hull design ever made with Gleam and VIM. I just need to resize the already drawn plans :
Your right on the last point Row, today just happens to be my last working day & going into very early retirement (Yip he!) and I will have all the the time in world to build of these wonderful boats and sail sail sail and did I mention sail !
Just calculated the actual static Righting Moment for the Australia II assuming a ballast of 4.5kg out of 6.3kg total Displacement. Ratio 7.14%
With the actual nominal keel ballast position the max Wind Speed acceptable for sailing should not go over 10.5kt and 45° of Heel.
I will calculate for a deeper keel ballast.
It should be also considered that the results are still optimistic since the reference rotational pivot should be around the LCB.
Australia II, that I decided to draw as first on purpose, is particularly penalized compared with other boats
…
Here below the Deep Keel configuration :
…
Comparing the two conditions, it is evident that the best gain at 45° of heel is only 1.5kt wind speed.
Probably not worthy to choose this solution unless more experts in this matter can show how similar models boats can afford in terms of wind speed.
As usual, I do not consider Hull Lateral Stability since at Model level Size is rather negligible, unless someone can prove the contrary !
All above is 'conditionally" based upon the assumption that the ballast can be of 4.5kg and using the remaining 1.8kg for the total construction of the model.
As comparison the complete 123cm Esterel Hull weight is 1.15kg and the bulb/fin of 3.0kg.
-Thinking about the Australia II
-I do not know much about the function of the wing of the keel, but I think it has a hydrofoil-like effect, which would give you an additional ascencion sailboat. Changing the displacement of the hull. Or maybe working on the contrary, like a dynamic ballast.
I wish You could explain a little how this works.
