No, more liekly it is the amount of sail area allowed under the class rule is one part, and the fact that a self-tacking jib as used on almost 100% of all the other model yachts is preferred.
You can divide up your jib into smaller sails if you care to, or make a quadrilateral, but I don’t think that you would gain anything from it.
Rule 3.2 says
Any sail plan that was used by the original boat from which the model was scaled, i.e. double head sails, Genoa, Spinnakers, etc. may be used on the model.
3.3 Maximum sail area for each model is as follows;
Whirlwind - Whirlwind and Vanguard hull - 2478 square inches
Whirlwind 1/16 scale - 4128 square inches
Weetamoe - 4247 square inches
Yankee - 4100 square inches
Enterprise - 4265 square inches
Shamrock V - 4241 square inches
Rainbow - 4238 square inches
Endeavour - 4253 square inches
Ranger - 4245 square inches
Endeavour II - 4243 square inches
So you can see that while you are allowed to use any sailplan, you are restricted by the total amount of sail area by class rule.
Personally… I don’t agree with this and I was talking about it with John Hanks earlier this week. I told him that I favored an increase in the amount of sail area carried and he told me the he would strongly oppose any vote to increase it. Any experienced J boat sailor will tell you that MOST of the time… the boats sail better (faster with more control) with less sail area than the maximum allowed… and this is true. However, I don’t see that the class should restrict you from using the scale sail plan.
If you were to run a scale genoa on say… Ranger… you would be carrying around 6000 sq in of sail when the legal limit is 4245, putting you almost 1800 sq in over… no small amount. John told me that the sq in was based on the sail that the boats carried when they were given their ratings. I don’t know who came up with the numbers or what they were based upon… but they are WAY low.
Also, if you are brave enough… Spinnakers are unmeasured and when Ranger ran up her chute… at 18,000 sq ft… it was the largest sail ever hoisted. These boats DESERVE to be able to run a full sized genoa… the performance increase is significant and the sight of a J boat with the genoa tucked in going to weather is just wonderful. You can use them if IN COMPETITION if you reduce the amount of sail area to conform with the maximum allowable.
Obviously… it has to come from the main… because otherwise you would have a self tacking jib with all the others. Sadly… the J boats are all heading the way of the other classes in that what was once intended to be a semi-scale class of elegant boats is becoming a development class with high tech light weight hulls and sails. Essentially they will become oversized “A” class boats. Spars are limited to wood and aluminum. This is why a minimum displacement was instituted some time back because of the trend to building extemely lightweight hulls.
I would not mind seeing them increase the minimum displacement to discourage this trend. No one these days seems to wants a scale model J boat, they want a high tech full race version.