As a quick refresher, these articles are about the building of a 1/16 scale radio-controlled model of the Swedish designed J Class Americas Cup racer designed in 1937 by Tore Holm and Gustav Plym. The 1/16 scale makes the model fit into the AMYA J Class for competition. My last article finished up 6 weeks after project startup with the planking for the plug of the 1/16 scale Svea not yet finished. As with any project, there were a few hiccups along the way, but as of this writing there are two complete hulls and more interest in the project than I anticipated.
The planking was completed on the plug and sanded to a smooth finish and the wood plug looked great. I had hopes of finishing the hull with clear fiberglass for a display piece so great care was taken to get just the right finish on the hull. Once cured, the fiberglass was wet sanded to a smooth finish and at that point the first hiccup appeared. There was a definite hollow in the starboard bow area, somehow the frames had been misshaped in that area. An attempt was made to fair the area with fiberglass, but the hollow was too deep and the thought of a clear wood hull was out the window. In order to turn out a good mold, the plug would have to be shaped perfect. It doesn’t really matter what color the plug was going to be, but the shape needs to be perfected. On went the body filler and more sanding followed. When everything looked perfect primer was applied and finally clearcoat.
Now the plug was perfect so the mold could be made. Since the hull has tumblehome the mold would have to be two pieces. The plug is now attached to the building board with two pivot points to allow for rotating the hull for easier access. The top of the hull has also had a 1-1/2 inch flange added to allow for the deck to be fastened. Of course, if you are going to build a mold from this plug, many coats of mold release wax must be applied to the plug to ensure that it doesn’t stick to the mold when you try to separate the two. Now a flange must be temporarily attached to the centerline of the bottom of the hull for mold building. This flange on the mold must also be strong enough to be bolted to the other half of the mold for joining the two hull halves after lay-up. Fiberboard and modeling clay was used to get the perfect mid hull flange and two locating cones were attached before the fiber glassing was started.
The first layer is black tooling gelcoat which is far harder and more brittle than regular gel coat, then a layer of light veil and 7 layers of fiberglass mat followed by a final layer of fiberglass cloth to smooth out the surface for easy handling. Simple right? Each layer needs to cure for a couple hours before applying the next layer so as not to build up too much heat and cause distortion to the mold so a few days were spent getting all of the layers on. The temporary mid-point flange was removed and waxed in preparation for the next half of the mold. Black tooling gel coat was applied to the remainder of the hull and allowed to cure. While everything is curing on the plug, eleven holes were drilled in the mid-point flange for bolts to be installed during assembly.
So there you have it, the abbreviated way to make a mold for an 8-1/2 foot boat. When the fiberglass had cured for a few days it was time to break the two mold halves away from the plug. The attached photo shows the mold halves and plug alongside the plastic tent that had to be built to heat the fiberglass for curing. Fiberglass cures best at 77 degrees and even here in California the night time temperatures in November were falling into the 50’s so some heating had to be applied for proper curing. Once the molds were cleaned up a little it was time to start a new hull. More wax is applied, allowed to dry, buffed and repeated for a total of 12 coats of mold release wax on the mold. This must be done to insure proper separation of the hull from the mold.
Off to my supplier for a batch of white gel coat, veil, mat and cloth to build the first hull. We are into December now and temperatures are still falling so the heating tent is playing an important part in getting everything to cure. I have found that after applying gel coat, it is best to wait 24 hours before applying any cloth. You want the gel coat to be pretty well cured so you don’t disturb the edges. On goes the veil, mat and fabric and low and behold, on December 10th we have our first Svea hull.
Remember those cold temperatures? Well it turns out that the mold should be cured for a month before trying to make a hull, otherwise you get a chemical attraction to the mold and your hull sticks. Yes, it stuck in about four places causing damage to the hull and mold. Both were salvageable, but it was not the results I had hoped for. At that time, I received an order for 2 Svea hulls and one Ranger hull so I moved the repaired Svea mold inside my office and set a heater for 80 degrees to further cure the mold. I prepped the Ranger mold with a newly recommended mold release wax and layed up hull #6. That mold is two years old, cured and the new wax worked wonders. The Ranger hull leaped out of the mold so fast I had to laugh. One more J Class boat done.
Now it’s time to turn my attention to the repaired mold, and start Svea Hull #2. This time nearly everything went well. A little sticking of the gel coat at the rear of the hull, but that was easily repaired and that boat has been delivered to it’s new owner. He will be building it with the help of our J Class secretary, John Hanks and hopes to have it sailing my March 10th, our next scheduled J Class race. I doubt that my boat will be done by then so I’ll be sailing my Ranger against his new Svea. It will be like an Americas Cup race from back in the 40’s. I’ll let you know how she sails in the last installment of the Svea Project.
Of course, with this project there are other matters to attend to. I had to design the rig and sails for the boat, enlarge the rudder so we have control (scale rudders have proved too small to control the boat in fleet racing), and calculate the ballast and placement. The sail plan is very similar to that designed or Ranger so with a 10’ mast we will carry a little over 4100 square inches of sail. The rudder was an easy redesign to increase the area and keep the curves in keeping with the design of the boat. I have a tank for testing ballast placement so that was filled with water and the lead weights prepared. Luckily, the ballast for Ranger easily fits inside the larger keel of Svea, so that was a great start. I placed lead weights equal to the weight of the rig at the designed mast location, added enough to make up for the deck and radio gear and it was time to get her sitting on the proper lines. The lead was moved around to get everything just right and amazingly, Svea only needed 1-1/2 lbs. more ballast than Ranger, The difference is, all of the lead sits much lower in the keel of Svea than Ranger’s ballast.
After getting the ballast location figured out, the hull was lined with plastic and the proper quantity of plaster of paris was poured into the hull and allowed to harden. The plaster was removed and cut into 3 pieces of nominally equal weight and molds constructed. So far I’ve poured two sets of ballast for Svea and the molds are holding up well and the ballast fits just right. The ballast was fitted in the boat while it was in the tank and everything looks just right so with a little luck Svea hull#2 should be sailing next month and hull #1 shortly thereafter. Hull #3 is headed for Chicago so those sailors should see a new Svea later this summer.
Copyright © 2018-2019 AMYA J CLASS - All Rights Reserved.