Hi Breakwater,
I have some doubts now about what expressed in the drawing above and the compliance with Marblehead Vintage Rules.
The Rules :
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Sliding or adjustable keels
Centerboards
Leeboards
Bilge-boards
Bowsprits
Overhanging rudders
Outriggers, pontoons, or twin hulls
Movable or shifting ballasts
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Now the above sketch refers to a movable keel/ballast to cope with taller mast or stronger winds.
If at a given regatta the boat is presented with one keel/ballast only, Fully painted and the joint invisible is acceptable or just because can be dismounted by releasing the nuts inside, the boat is not accepted ?
Further, a new regatta some weeks later a will present with the same hull and rig but this time the deeper keel/ballast is attached, joint painted and not visible, what happen ?
Finally I managed to compose the EC12 side view and calculated the static Righting Moment see below :
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Then I reduced the same plan to the size of 1270mm of length and redrawn the Sail Plan and measured again the RM.
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As can be noticed, reducing the scale, the acceptable wind speed is reduced by about 1.0/1.3kt
This is valid at the condition that the ballast is set to about 4.0kg to avoid eccessive keel form deformation while the scale conversion would suggest 5.2kg .
Assuming 1.7kg for the construction, the total DSPL should be 5.7kg.
The nominal Endeavour II DSPL without any modification is actually 4.65kg , that means that the keel shall be modified in order to increase the DSPL .
I shall give a try without producing an horror playing with the deeper keel and shadow underwater forms !!!
Discussing with a friend about the acceptable wind speed around 7/8kt for 30° of heel is considering that is already a very good performance and because of that it is not necessary to go any further.
The EC12 is accepting 8.3 knots of wind speed for 8.25kg ballast (18.2 lbs).
I shall adds also that this method of calculation is based upon the Bernoulli law where the wind is producing a pressure against an orthogonal surface (90°). Practically this is not the same condition for the sail, where the apparent wind is applied with a different angle (~15°/20°) except when running where the boat speed shall be considered too.
Summarizing, the Static RM method used, while approximate it is also very conservative.
As often said the boat width is not considered since the form stability is negligible as well the meta-centric height.
This give margin to believe that the models can sail comfortably under the calculated conditions.
Yes, You are right on that. It would no-longer qualify as a VM, which I why I had mentioned the design would be pushed forward in the Class to a modern category of the Marblehead. Similar to that of your AZUR design.
Hi Breakwater
may be “cool”, but not usable ! heheh
I reworked the full Endeavour Design and think I found the solution I was searching for.
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The displacement achieved is 5.9kg and the Ballast is 4.2kg with a ratio of over 70%.
As a matter of facts, I fully redraw the shadows retracing the original picture, see below.
I split the above water shadows from below water shadows, in this manner I could exercise the “stretching” function only on the immersed ones.
With various calculations via the Curve of Area I selected the draft of 170mm against the original (after scaling) of 144mm. see screen picture.
The Aesthetic is saved as well.
Actually the max Beam is +3.9% wider and the draft is increased by 18%.
Here another one, the revised/re-scaled AMERICA EAGLE from the existing drawings.
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Interesting Displacement and Ballast weight as per Australia II.
The specific long keel produce also a recessed LCB and possibly the LRC is also recessed as well, therefore the RIG mount is moved backward too. Unfortunately while the directional performance may be improved, the Wet Area is also increased.
Thinking about a possible modification like depicted below with shorter keel. The DSPL may loose some cm3, but not many, while the Wet Areas will be reduced. Hope purists will not be solicited ! hehe!
So, is that Endeavour ll ready to go.now?!! The reworked displacement draft & beam etc certainly haven’t detracted from the aesthetic qualities of the original so congratulations!
I see from the hull data that both displacement & ballast (& ballast ratio) are all higher than your original ‘Enterprise’ drawings despite the shorter LOA. Does this mean that if you were doing Enterprise again (still at 1:28) you would try to further increase the ballast ratio?. I only ask because at the moment my total ballast weight is around 350g over - I cast it oversize to enable trimming etc - therefore giving me the opportunity to retain additional weight where it’s needed (down low) always assuming I can keep the construction weight down, which is something of an unkown quantity at the moment.
Was a demanding exercise to control both parameters for the Endeavour.
The ballast increase of the models of this tread is more dictated by the intention to keep as close as possible all models inside a certain range.
As you may have noticed, the scaling of 12Metres show a relative larger displacements and therefore the idea to get the ballast weigh up is a normal temptation.
I should not design a ‘New Enterprise’ of the same length of 131.5cm since a fin/bulb could be used to increase the righting moment. The original model was 5810cm3 and modified the keel draft from 160mm to 200mm to reach the actual 6167cm3.
The Mast height or Sail Plan can be modified if desired.
The Enterprise that, you and me, we are building, do not respond to any Rule so we are free to do what retained more convenient without increasing, of course, the total displacement to avoid sinking the water line and loosing sailing capability.
The actual development suggest the full construction to be kept inside, as rule of thumb, the 1750g
As always, more grams gained in the construction and more grams can be transferred to the ballast.
I recall that each 1mm adjacent variation of the your Enterprise Water Plan is equivalent to 135g, thus 5mm will be equivalent to 635g and the LWL will increase by 36mm. Of course the drag will increase as well the relative speed.
The Enterprise was modified from the original with deeper draft to have a displacement of 6167cm3 and a Ballast of 3900g. The construction was estimated for 2267g.
If you manage to make the full construction with 1800g, this mean that the difference can be used for the ballast : 2267 - 1900 = 367g and this case the ballast can be 4267g that will produce a Ratio of 69% . The transfer of additional 100g is sufficient to produce a ratio of 70%.
There is another observation that was clearly appearing with the EC12 scaling as depicted previously, and this regard the original EC12 model with 149cm of length that appear to be more “stiff” then the scaled down EC12 to 127cm. This is visible from the Static Righting Moment calculation.
In other word there is a direct relation between the boat dimensions and the Righting Moments at constant scale.
This is the AZZURRA that will be the last design/drawing. Missing complementary data like the DSPL , Ballast and definitive detailed Shadows :
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ClaudioD
PS :
Missing file Endeavour Shadows to 1:1 scale
Missing file American Eagle Shadows to 1:1 scale
Missing review for Ranger Displacement & possibly new Shadows to scale 1:1
Missing review for Azzurra Displacement & Shadows to scale 1:1 and Deck layout
Like you, I also prefer the aesthetics of Columbia and American Eagle (although the other way round), but I also think they’re a bit too similar to the J class. For that reason alone my preference would be to see Azzurra / Australia ll on the lofting floor first.
Hi Row,
just added the J Class that I couldn’t put on the same page and the Endeavour is very nice too but probably suffering the bow height from the water.
This aspect can always be modified without disturbing the all look. The difference with the 12Meters is about 12mm or 12%
The American Eagle being the highest above water.
Cheers
ClaudioD
while not entirely on topic… i have wondered. what would the J and 12’s look like today. IE use the old rules and build a modern J class. or modern 12 full size. modern materials.
Well, if use the 6 meters (http://www.6mrnorthamerica.com/) as a reference (like an old class/rules but still actively - relatively - sailed and build), they would most likely not be much different from the “older versions”.
Hi Earl,
this is what I have already done with the Endeavour and I will repeat with the Ranger.
For the 12Meters, except what not yet done like the Azzurra, all others have already a relative wide fin at bottom area. Probably a small modification needed for the Columbia as to reach the 5.9/6.0kg displacement.
This is the technique I use with the envelope function of CorelDraw 5 where I can modify the shapes with progressive evolution and without disturbing the lines character :
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The intent is to reach similar Displacement in the range 5.9/6.2kg and a ratio of 69/71%, being the Sail Area = 800in²
The actual values are :
Endeavour II …5869cm3
Ranger …4673cm3 need to be modified as already done with the Endeavour by ‘stretching’ the immersed volume
American Eagle…6275cm3 may be a small modification (shortening) of the keel length from the rudder side
Columbia…5768cm3 small additional DSPL increase needed
Australia II…6300cm3 the heaviest
Azzurra …~5350cm3 to be modified yet
It never ceases to amaze me what can be done with a graphics package - obviously they’ll only do what there told, but still … I just wish I had the patience to sit down and get to grips with one of them. I sort of managed it with Google Sketchup approximately 7 / 8 years ago, but that was designing a conservatory which is all straight lines - simple by comparison to the manipulation of hull line drawings, which may as well be a form of wizardry as far as I’m concerned!!
Keep up the incredible work Claudio,
Regards,
Row
Edit: Just re-read post 252 where you’ve expressed concern about the height of Endeavour ll’s bow above the water. From your drawings I see that it’s at 77mm (against Ranger at 78mm) neither of which looks particularly high - so from an aesthetic view point I really don’t believe either require any adjustment. To put the dimension into perspective, Enterprise at 1315mm LOA has a bow height in excess of 80mm (it may be as much as 85mm, I don’t have the drawings to hand at the moment). I think it’s also worth pointing out that ‘in the flesh’ when viewing a J from a side profile the bow has the appearance of looking a little high owing, I think, to the fine profile. Either way, I really don’t think any further refinement is necessary. R.
marksmith: check out the F-class Firefly built by Hoek Design. Also, not very many new six meters and 8 meters have been built recently. Two of the eight meters looked classic on the top side and had modern keels on the bottom.
Hollandia, Gannymede and Spazzo are three very modern designs (possibly 2 or 3 more).
Also, a new 5.5 meter (a slightly different rule than the 6, 8, and 12 meter rules) has very modern attributes, much like the AC boats 2003 to 2007.
I’m sure the 12 meters would look similar, although what works for 6 meters doesn’t always hold true for 12 meters…see Sparkman and Stephens blogs about that.
Claudio:
1)Australia II the heaviest because it was the shortest?
I guess I don’t follow what you are talking about in regards to the bow of endeavour being up too high…Is it because of the bouyancy distribution changing with the different keel configurations?
