Building a J Class Model

By John Hanks III


Now you may be wondering what is involved in building a model of a J Class yacht. I will give you an idea of what is involved in getting your J model in the water.

To begin with, let me say that you will need to do some scratch building to get your J model completed, regardless which yacht you choose to model. The scratch building will involve the deck, the rig, and probably the hardware associated with the mast, boom and rigging. With that said, you will need to decide which yacht you would like to model. In the full size J Yachts there was a definite advantage associated with which hull was in the water, but with the models, it appears that any of the J designs will make a good fast sailing model, if it is built correctly. So your decision should be driven by your personal preference for a particular boat. Once you decide which yacht you would like to model you will need to either buy a fiberglass hull or get the drawings for your chosen hull.  There are hull line drawings available in the proper scale for all of the J's as well as some deck plans. You can get line drawings from several of the maritime museums, such as the Mystic Seaport Museum.


The amount of time that you will spend on building your model will vary with your building ability, whether you start with a fiberglass hull and how much detail you want to put on your model. Should you decide to scratch build the entire model with a lot of detail, you should plan on spending about 500 to 550 hours building your model. If you begin with a fiberglass hull, subtract about 150 hours, if you do not want to detail your model, deduct about another 100 hours. The cost of materials will be about $800 to $900 if you decide to completely scratch build your model.


I will begin the actual building process with a plank-on-frame hull. You can skip these steps if you start with a fiberglass hull. The process for completing the remainder of the model will be the same from that point on.


To begin the building process, you will need to get your drawings ready by extending each frame to a “waterline” that is above the deck line on the drawing. This new “waterline” will be the part of the frame that rests on the building board. The new “waterline” gives you a flat plane so that all of the frames are referenced to the building board surface, while allowing the arc of the sheer at the deck line to maintain its shape. Your modified drawing should show the hull shape, the shape of the deck beams, and the building board surface.


You will begin the building process by building a building board. The easiest way that I have found to do this is to buy an 8 foot long 4”x6” and mount it at a convenient building height on 2”x4” legs. You will need to make sure that the 4”x6” plank is straight and true and that it will stay that way through out the building process, as this will determine the trueness of your model.


Mark a centerline on your building board and then mark all of the station locations on the centerline. You will then need to draw a line perpendicular to the centerline at each of the station locations. You will next attach small blocks (approximately 1-1/2 x 1-1/2 x ¾  inch) to the building board on the centerline and aligned with the perpendicular station lines. The blocks need to be placed so that the frames that will be glued to these blocks will be centered on the perpendiculars.


The next step will be to cut out the frames that will form the hull. For this step you will need to keep in mind the difference between the line drawings for a metal hull versus a wooden hull. The drawings for a metal hull show the frames to the outside of the plating and for a wooden hull, they are to the outside of the framing, not the hull planking. This will make a difference in your model, as all of the Js were metal boats, and if you draw your frames to the lines, your model will be oversized by the thickness of your planking.

I use 1/8 inch Luan plywood for the frames. The plywood comes in a 4’x8’ sheet and I can get all 28 to 30 frames from one sheet of plywood. The frame patterns are cut from your drawing, and each frame pattern is traced on the wood. With careful placement you should have no trouble getting all of the frames traced onto the plywood. You will need to draw the cutouts for the keel, inwales and king plank in the frame tracings. The centers of the framed are also cut out so that you end up with a ring of wood that is about ¾ inch from the outside to the inside of the frame. 


When I cut my frames I do not try to cut on the line that I have drawn; I am not that good with the saw. I leave a little wood, about a 1/16 inch next to the line and sand the frame to the final shape. I find that this makes it much easier to control the accuracy of the frame shape. Once all of the frames are cut and notched for the keel and inwales, they are glued to the blocks on the building board. At this point you should be able to sight down the frames and get a good idea of the shape of your hull.


With the frames glued in place, you are now ready to install the keel and the inwales. I like to use ¼ inch birch plywood for the keel and 1/4x1/4 inch square for the inwales. The inwales can be cut from the same material that you will use for the planking. The hull framing is very limber at this point but it becomes very ridged once the keel and inwales are in place.


The hull is now ready for planking. I have used pine, bass, aspen, spruce and alder for planking. All work well. The availability and price of the material is what determines which material I use. When I built my first J some 30 years ago, clear pine in 8 foot lengths was plentiful and inexpensive. Since then, it has become hard to find and very expensive. As a result I have used other woods that were available, hence the bass, aspen, spruce and alder. The planking material is cut into strips that are about 5/32 inch thick and 3/8 inch wide. This is a nice working size, as the planks are limber enough to form to the hull without the need for spiling (tapering), wetting, or steaming them. You will start the planking at the first frame and end at the last. The 2 to 3 inches of hull that remain at the ends will be filled with solid wood blocks shaped to the dimensions of the hull. Begin planking your hull at the sheer and work to the keel. Each side of the hull will require about 50 to 60 planks. Remember that you will need to alternate sides of the hull as you plank so that you keep the stresses equal on both sides of the hull, thus preventing distortion in the hull. 


You will need to change direction of the planking when you get to the bilge area of the hull. The planking will take on an increased twist towards the stern that will prevent the planks from laying fair. The planks will tell you when you have reached this point, usually about 15 to 20 planks up on the hull. To overcome this you will need to lay a plank in a straight line along the hull so that it lays flat between the areas where the existing planking meets the keel. This will leave a lens shaped gap of about 4 or 5 inches between this plank and the existing planking at the middle of the hull. Fill this area by planking from the new plank that you laid down to the existing planking. Once you have completed that step, then continue to plank the rest of the hull. When you have finished your planking, you are ready to attach the bow and stern blocks, shape them, and sand the entire hull to get it ready for fiber glassing.


I like to build the rudder next and fit it to the hull. I build the rudder as I would build an airplane control surface, with a leading edge spar, three ribs, and a trailing edge. The framework is then covered with 1/32 inch plywood. The square tube that accepts the 5/32 inch brass rod rudder shaft is installed in the leading edge as well as the pivot pin at the bottom of the rudder. The hull is drilled and the rudder log is installed and the rudder is fitted in place. Once the rudder is fitted and works well, the hull is fiber glassed using a single layer of 6 ounce cloth and three to four coats of resin. Each coat of resin is sanded before the next coat is applied. When the sanding is complete you will have a smooth and fair hull that will look great when it is painted. The hull is now ready to be removed form the building board. At this time, you should also have a stand built and ready to accept the hull. 


Once the hull is off of the building board, it is time to seal the inside with epoxy and install the mechanical workings in the hull as well as install any reinforcements that are needed, such as at the chain plates, mast step, and sheet exits. From this point on, the building process is the same for the fiberglass hulls once you have the deck beams in place. This is also the time to lay out the hatch openings. When laying out the hatch openings you want to keep them as small as possible and still be able to do any work inside the hull that is necessary. Nothing is more frustrating than to find out that you cannot reach some part of your equipment once the deck is in place, so be sure that you can work on and remove and replace all of the fittings, winches, ballast, etc., through the hatch(s) that you have framed in your deck. 


Building the deck is the next big step in getting your J ready to sail. There are several different ways to build your deck, and your decision on how much scale detail you want on your model will drive part of that process. If you want a slick deck with no scale detail, then a simple plywood deck will do. The 1/8 inch plywood will be more than adequate for the job and can be finished so that you have a very good looking wooden deck on your model. 


Another option is to build a plank deck that represents the deck on the full size yacht. If this is your preference, then you begin by cutting the deck planking to the same dimensions as the hull planking. I cut my planks to a length of 15 inches so that I have scale 20 foot planks. To simulate the deck caulking, I use black construction paper glued between the planks. Once you have the planking cut, you will need to lay the king plank down the center of the deck and the water way planks down each side of the hull. All of the Js had the planking run parallel  to the edge of the hull, so you will need to begin laying your deck from the edge of the hull, and work to the center. The paper between the planks helps the glue, thin CA, flow and form a good bond at the seam. From this point on you just continue your planking until the deck is completely covered. As you build your deck you will need to cut your planking at the hatches so you will have access to the inside of the hull when you have finished your planking.


When the deck planking is complete, you will sand the whole deck and get it ready for finishing. At this point, you should have a great looking model. 


Again your decision on the amount of detail that you want on your model will determine your next step. If you opt for a scale appearance, by this time you will need to make the cabins, deckhouses, winches, cleats, and anything else that goes on the deck.


The hull is now ready for finishing. I use non-water-based, clear gloss, polyurethane on the deck, cabins, and spars and automotive acrylic enamel for the color on the hull. These make very nice durable finishes which should last many years on your model. I chose to use polyurethane because it does not yellow like varnish does as it ages. This is a personal choice driven by how you would like your deck to look as it ages.


At this point you will have to ballast your model. I have found that the easiest time to do this is after the model is painted and has the scale waterline in place. Place your model in a swimming pool or other suitable tank, and place the lead in the hull until the hull sits on the waterline that is painted on the hull. You will need about 60+ pounds of lead in a manageable form, about 5 pound pigs, for this exercise. Once the lead has been placed in the hull and the proper trim established, you will need to note where the lead is in the hull and the amount at each location. You can then remove the lead from the hull and using your notes, make molds for the ballast so that it fits into the hull cavities. 


The next step is building your rig. The masts for the J models will be anywhere from 8 to 91/2 feet tall, depending on which boat you are building and how you lay out the sail plan. For support, the mast will need at least two sets of spreaders with accompanying side stays, and a diamond stay. I have used both aluminum and wood to make J masts. The last mast that I built was made from spruce and was 109 inches tall, with a tear drop cross section that measured about 1-1/4 x ¾ inches. The mast was tapered in its top 3 feet and had a bolt rope slot cut in it used to attach the main sail to the mast. The mast was made from two pieces of spruce that were glued together on the centerline with the grain in each piece set so that any warps canceled each other out. The result was a stiff spar that weighed about 1-1/2 pounds ready to step on the deck Extruded aluminum masts are also available in lengths up to 10 feet, from Ludwig Manufacturing. These masts have a bolt rope slot molded in them and are both light, about 1 pound for a 10 foot piece, and stiff.


The main boom and jib club were both made from spruce. The jib club was about 33 inches long and 1x1/2 inch in cross section and tapered to 1/2 x1/2 inch at both ends. The main boom was about 45 inches long and was about 1 inch from top to bottom with a scale cross section that resembled an old wine jug. These shapes were made for a model of Rainbow.


The gooseneck attachment was made for a piece of ¼ inch thick aluminum plate and secured in a slot cut into the base of the mast. The gooseneck and boom vang pivot on a single stainless-steel rod, (welding rod) about 3 inches long. The boom can be removed from the mast by simply pulling the pivot pin; then the gooseneck and vang are released. The sail can then be slid down out of the bolt-rope slot and rolled for storage.

This is a quick overview of the building process that is needed to build a model J boat. 


Below is a list of most of the materials that were used.

WOOD

2 – 1”x8”x8’ pine, aspen, bass or other suitable wood that can be cut into 5/32”x3/8” strips for hull and deck planking

1 – 4’x8’x18” plywood used for hull framing, 2 if you are using one for the deck

1 – 1’x4’x1/4” five ply birch plywood for the keel

1 – 1’x2’x1/32” plywood used for the rudder sheeting

1 – 1”x4”x8’ spruce for the mast and booms (optional if you are using an aluminum mast)

METAL

4 – ¼”x12”x.030” brass strap used for chain plates, mast, and boom fittings

1 – 1/8”x3’ stainless steel welding rod used for gooseneck pivot and spreader stubs in the mast

1 – 1’x6”x1/4” aluminum plate used for the gooseneck and vang fitting (use only if you are scratch building the fittings

1 – 5/32”x12” brass round tube used for spreader bases

1 – 3/16”x12” brass rod used for the rudder shaft

1 – 7/32”x12” brass round tube used for rudder log

1 – 3/16’x12’ square brass tube used for the rudder shaft socket in the rudder

60+ pounds of lead used for ballast

GLUE

4 – 8oz bottles of thin CA used for planking the hull and deck as well as general construction

 1 – 2oz bottle of medium CA for general construction

32oz of 30 minute or longer set epoxy used to seal the hull interior

FIBERGLASS

1 – 10’x50” 6 oz fiberglass cloth used to cover the outside of the hull

2 – Quart cans of polyester resin with catalyst used with the fiberglass cloth

6 to 8 – 2” disposable brushes used to apply polyester resin

HARDWARE

8 – Turnbuckles used for the side stays, boom vang and diamond stay

36 – 1-72x 1” stainless steel machine screws with nuts and washers used for various attachments

90’ – 60 pound test nylon coated stainless steel fishing leader with swages used for the standing rigging

8 – Single blocks used for back stay, winch arm, up haul and rudder control

1 – Spool of 40 to 60 pound test braided Dacron line for the sheets

12 – Bowsies for various rigging adjustments

Reference Information

Reference book: Enterprise to Endeavour by Ian Dear, ISBN 1-57409-091-7

This covers most of what you would need to build your J model. I did not mention the wood or brass that I used to make the scale detail, as most of it was obtained as scrap from a cabinet shop and salvage yard. Some additional things that you will need are a radio (at least 2 channels), a quarter scale servo for the rudder, and a sail winch, either arm or drum with about 3,000 inch ounces of pulling power. You would also need to order your sails from your favorite sail maker.


I hope that this answers most of your questions about what it takes to build a model of a J Class yacht. By the way the process described above applies to scratch building any R/C model sail boat, the only difference is the scale of the project. Good luck with your building project


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