Understanding the AMYA J Class Model

By John Hanks III

Understanding An AMYA J Class Model

Let me begin by saying that the AMYA J Class models are BIG. The J Class models are 1/16th scale models of the full-size J Class yachts that Raced for the America’s Cup in the 1930s.


 The full-size yachts were between 120 and 135 feet long and after doing the math, that gives you a model 90 to 101 inches long. To put that in perspective, that is as long as two Marbleheads end to end. In fact some of the J models have main booms as long as a Marblehead. 


The weight of the Js, when they are ready to sail, matches their dimensions, with the lightest being about 65 pounds and the heaviest about 95 pounds. 


The masts are also huge, ranging from 8 feet above the deck to over 9-1/2 feet above the deck.


The size of the models and the fact that they have scale hulls presents some unique problems for the J owner. Probably the most obvious question is “How do I get my model to and from the lake?” Well it takes a little planning and a large vehicle of some kind. I know of J owners who have purchased trailers for their Js, while others transport their model Js in full-size pickups or vans. I have also witnessed a J model arrive at a regatta, from Oklahoma, in a mid-size hatch back, with the stern resting on the dash and the bow just under the hatch glass on in the back. I can imagine how that affected the conversation between the driver and passenger. I carry my J models in a 1956 Chevy station wagon. It was a great excuse to buy a classic car. 


The next question is “How do I get my 90 + or – pound model in the water once it is ready to sail?” Well it takes two people that are willing to lift your model and carry it to the water and then not mind getting their feet wet as they set it in the pond. Hopefully you have brought that willing individual with you to the pond so you do not have to persuade a by-stander to be your assistant. I am very fortunate in that my wife, Barbara, is always a willing deck hand when it comes to working with the models. 


The scale aspect of the model produces some handling characteristics that are somewhat different than those associated with a modern fin-keel model. When the boats are scaled down, and this is true of any scale model sailboat, the wind and water do not scale down in the same proportions. You lose stability in the hull faster than you lose the power of the wind in the sails. Several things come together in a model J to help over come this phenomenon. First, the percentage of ballast weight to total displacement is much different in a model J than a full-size yacht. The full-size yacht is doing well to get 40% of the total displacement in the ballast, while a model J can get 70% or more in the ballast. 


Second, the J Class allows a 2 inch extension to the keel depth to increase stability. This adds to stability in two ways; first it lowers the center of gravity slightly; and second, it adds volume to the hull, which needs added ballast for the model to get to the proper water line. The 2-inch keel extension forces the addition of between 5 and 10 pounds of ballast to the total displacement over and above the scale displacement. Most of the model Js also sail with a reduction in sail area compared to a truly scale sail plan. Most of the model Js would carry about 4,200 square inches of sail in a full-size, scale sail plan. The best all round sailing model Js carry a sail plan with about 3,500 square inches on the larger models, such as Ranger or Endeavour, and 2,900 square inches on the smaller models such as Shamrock V or Enterprise. This change allows them to sail in a fairly broad range of wind conditions.

How do the boats handle on the water?


 In short, they sail and handle like a big boat. They do not turn on a dime like the smaller fin-keel boats most of us are used to sailing, so it takes a little planning to get around the race course, especially if you are in a fleet. The models are deceptively fast because their great size fools you into thinking that they are moving more slowly than they actually are. 


All of this takes a little getting used to for the first time J skipper, but all of the skippers who have sailed a model J get to love it very quickly. Most of the skippers cannot get over how stable and solid the boats feel. They are not twitchy in the puffs, within reason of course, and they handle with light control inputs.


The majesty and grace of a J Class yacht on the water carries over from the full size yachts into the models. It is hared to describe the beauty of a fleet of J Class models as they make their way around the marks.