J-Class versus 12Metre Class

Other America's Cup Boats
101

Hi Alan,
my intention is to use, if advantageous, lead shot for all models, so far the Center of Gravity is achieved without additional moving ballasts.
Volume is the matter of concern since I found also that lead shots can be as low as 4.4kg/dm3.
I would like to avoid casting because is dangerous for non expert people, I would of course choose the slice method as I always use.
The particular AUSTRALIA II keel could made with a two parts mold including the wiglets.
Melting foam with acetone is damaging also the laminate and it is a dirty job IMO.
I would suggest a silicone mold as depicted below.

I will see what I can do to render the life easy. The keel could be an ‘added-on’ part as the red lined profile in the image below :

Cheers
ClaudioD

BTW : High Temperature (310°C) Silicone molds can be used also for ballast lead melting !

102

Excellent idea !!! then the builder can choose what ever option they like to use.

To-date never come across problem with acetone it damaging laminate … but it does eat gelcoat !

I use keel fins that have a foam core, dissolving foam with acetone can be messy if you don’t use enough acetone, otherwise it is clean to work with. Why ? you can clip on slightly under weight bulb (less wetted area) and bring the ballast exactly back up to race weight by adding lead inside the fin void.

103

Alan, probably the previous drawing is misleading, better to see this one :

See also here some examples of hollow keel : http://www.rcgroups.com/forums/showthread.php?t=475185

Only part of the keel is filled up with lead shots and the total mass shall also be positioned as such to get the CG at the right place.

This solution is in any case linked to the possibility that any one can procure the Lead Shots of the correct weight.

I’m not sure to have understood what you means by “lead shaving”

The use of Silicone Mold make rather easy to extract the lamination even with tilted portions like the widgets.

ClaudioD

104

[QUOTE=claudio;66913I’m not sure to have understood what you means by “lead shaving”[/QUOTE]

When I make a lead bulb I always pour it so it is little heavier than what need (safety factor) then I shave and rasp then file off the excess lead into final shape before fairing the bulb, it is this that can be used instead of low density lead shot pallets to fill the void in the keel.

The hollow keel illustrated in your drawing above & shown in the link, is exactly what I was thinking

105

Understood, but before getting an average of 2.5kg there is need of a lot rasp work ! heheh!!
In the picture below show what I do not want to do.
The lead weight should be positioned as low as possible inside the hollow keel body.

Pity I do not remember the formula to calculate the plain ball volume with the air interface between balls.
I should go back to school !!
ClaudioD

PS :

Found the little formula to calculate the volume occupied by the balls in a cube : Volume = 3.14 / 3 x 1.4142 (sq-root of 2) = 0.74

Therefore the weight per volume is : Lead weight x 0.74 .
In the case of lead shots of 6kg/m3, the real useful weight per volume will : 6 x 0.74 = 4.44
That’s means that the required keel volume shall be more then the double.
More I dig in the subject and more I find difficult to cope with the design unless the lead weigh is close to the theoretical value.see : http://www.amexresources.in/lead-shots.html

106

Yes agree want to keep C.G as low as possible.

The other point is how to fix the keel to the hull, was thinking maybe a good idea to have keel plank between shadows 5 & 6 (bulk heads) that the keel bolts to, this would lower C.G further and leave more room below the deck for servo & radio equipment etc.

My concern with the big rod shown in concept drawing above is that if you over tighten it, you could possibly stress or distort the hull ?

107

Yes You are right !
here how can be done :

…
You may find on You Tube a lot of footage about “making lead shots”, interesting ! Some others use metal mesh !

claudioD

108

Just keep in mind that Australia II won’t qualify as a Vintage Marblehead… due to the non-prognatheous rule.
Not a big deal though… It’s only one of the three design types you are discussing. Those being J-class, 12 Meter Long-keel and 12 meter Short-Keel.

109

Hi,
This is a good new ! heheh !!
Much less work for me then …
ClaudioD

110

Hi Claudio,

Maybe the rod needs to be at the bottom of the hull where you can then spread the keel weight load on hull better, I would fear a suspended keel weight below the keel/hull junction would poosibly be problematic.

Hey an idea :idea_125: talking about the modern 12 metre, what about 1 hull design where you have option to change only the keel ala Victor idea

Then the user can change paint scheme and keel to have Aussie II, Azzura or what boat they like.

To make the class really distinctive you could think about integrating the Ramoser Sprinta Genoa system, as now there is the option of RMG & Italian S330 to choose from. From my experience the Genoa is a step-up that is a lot closer to big boat sailing compared to the traditional RC Jib boom and it would really suit the classic modern 12 metre design.

Pushing the envelope further one could even think about using all the rigging, sails, mast, quick snap turnbuckles etc that is all available from the Sprinter as accessories, only question would is would the Sprinter sail plan be suitable for modern 12 metre design ?

Cheers Alan

111

Hi Alan,
various technical solutions can be found being the Australia model a particular one.
Not to forget that partial shadows are going down to the keel for local reinforcement. Not excluded to inject foam also.

In principle, I do not wish to deviate from the Marblehead “50/800” - VM Rules, unless other ideas come to the light in order to establish a common consensus.

As Breakwater said, the “50/800” is the most popular model boat other then IOM, and I like the idea that other models classes like J-Class and 12Metres being compliant with that Rules, including competitions.

One could also invent a new Class called for instance “800/50” where other options could be introduced including the possibility to change the keel form against the “non-prognathous” rule and add Genoa and multiple Jib functions.

Australia II is a particular case that ‘could’ be compliant only with the potential ‘new class’ “800/50” unless the winged are removed with the use of another keel design.

Hope others may make other proposal for discussion.

Certainly the 50" - (127cm) length is an interesting technical and dimensional option while the 800in² is a comfortable dimension.

Cheers
ClaudioD

112

Have sailed an RC boat with a genoa, I much prefer boats that have self tacking foresails. With a genoa, you have to haul it from side to side for every tack, not as relaxing because you are forever worrying about which side the sail is…and gets more confusing when sailing back toward you as everything is reversed…

A genoa looks nice and goes well when correctly set up…

113

Attentions Please !!

All the Images loaded at full page with Image-shack are removed from the stored album by mistake and definitively lost.
Thumbs images are kept being stored with RCSailing server.
I’m very Sorry !
ClaudioD

PS:
I will try to recover the boat side views and the last Voting Table

114

Here the images for the J Class side views
ClaudioD

115

Here the side view for the 12Metres “long keels” before the launch of Intrepid.
ClaudioD

116

Here the sides views for the 12Metres "short keel & Trim-Tab launched after the Intrepid.
ClaudioD

117

Votes Standing :

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ClaudioD

118

All plain page images of this tread are restored
ClaudioD

Lucky me, thanks to Image-shack all images files have been restored !!!

119

Started with Australia II drawing scanning and reported to CorelDraw for retracing to the requirements !

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ClaudioD

120

Dear Claudio,

I have been thinking about a possible class of model sailboats that is nearly the same as what you are presenting. If instead of a loa or lwl limiting parameter, what about a class built around the actual meter rule, with a value of .7, .75 or .8? I was thinking about this with more interest in 6 m and 8 m yachts. One challenge would be freeboard however, as the freeboard for each class is not proportional between the classes…6 meters have greater freeboard than the 8 and 12 meters. Draft is not proportional either, but that probably needs adjusting anyway.

This class could then inspire new designs as well as using existing drawings, and it too would be broken into a pre intrepid and after class.

In addition, even J boats could participate in the racing, as long as the sail area is adjusted and they are measured to the meter rule…but they have even less freeboard than a 12 at the same length.

On another note, there is a forum about Austrailia II in RCGroups at the moment, a large model the same dimension as an EC12.

And, the Cantebury J is very similar to the size you are proposing for these boats, and could be used as guide or trialhorse…48 inches long, 8 inch beam, and about an 8 inch draft.

As for the vote, I would cast for:

Jboats:
J8 Atlantis, FC Paine
S1 Svea Tore Holm
Eneavour II Nicholson

12 meter
Steak and Kidney (this one was supposedly faster than Kookaburra III, and worried D. Connors)
Freedom
Intrepid

and what about the ‘Geek’…SFYC controversial bulb with back and front rudders?

and there’s always Mariner!!

pre Intrepid
Constellation ( S and S)
Vanity (W.Fife)
American Eagle (Luders)