J-Class Jib

I have a question maybe someone can enlighten me on. I am looking into doing a J-Class Shamrock boat this winter and I would like it to be as scale as possible. On the actual boats, they had 3 jib sails out front of the main. But on our J-Class models I see one single jib sail. Is it just the difficulty of controling three separate sails?



Will it be 1:16 scale Shamrock?

My next project is a J Boat probably Endeavour II (1:16 scale)
I will be looking at using the multiple jib setup, as I want to look authentic as possible and go away from the single jib and boom setup.

Got some throughts on how to do it, but nothing sketched as yet.


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.

PS… if the weather cooperates… watch for pics of Ranger running that genoa. I hope to have them taken this weekend. Yea, all 6000 sq in of sail on that bad boy.

I dunno that minumum displacement would be the answer

I remember the mumms i used to sail on was underweight , and just had 2 blobs of lead bolted on to the sub floor just near the keel , even w/o changing the underwater shape , u can still try to get the most weight were u want it via building a lightweight boat , then adding weight to a favourable area

I don’t know if it was the answer, but it is the class rule.

Actually the way that the J class measures sails, you would have a very difficult time to max out the allowable sail area. I would say that you could get away with a triple headsail with no problem. Your boat will not perform as well though and will end up with a very poor VMG against a single headsail.

I don’t know how you are measuring, but John Hanks agrees that 1/2B(H) is used. With that yes, I totally exceed the 4245 for Ranger with a total of 6000 sq in, and no the boat is not slow in very light air < 5kts which we have here quite often particularly in early evening.

It walks off and leaves Rainbow which is 13lbs heavier in even the lightest puffs.