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Forward Web, Centerboard Well, and After Spine Assembly Three major assemblies, when joined, the forward web, centerboard well, and after spine assembly, make up the central support of the Fireball. This unit is the basic profile shape of the boat from which the rest of boat evolves. The forward web and after spine are constructed in a similar fashion to one another. They are made up of a sheet of 4 mm plywood sandwiched between solid lumber supports outlining the shape of each. The centerboard well is two identical pieces of 6 mm plywood separated by two solid lumber spacers to hold the two pieces apart providing a space for the centerboard to pivot between the plywood pieces. The centerboard well is slotted at the forward and after ends to allow the forward web and after spine to be assembled together with it creating one strong and supportive unit. The centerboard well is constructed of 6 mm Okoume plywood with western red cedar used for the packing pieces and African mahogany for the centerboard well caps and case logs. The forward web is constructed of 4 mm Okoume plywood with western red cedar used for framing and stiffeners. The after spine is constructed of 4 mm Okoume plywood with western red cedar used as framing. The after spine is really only used to hold the shape of the rocker while building the boat. After a certain point during the construction of the Fireball, much of it may be removed to save weight as it will not increase the boat’s strength. Begin constructing the forward web by selecting a sheet of 4 mm plywood and placing the paper pattern on top of the plywood. Line up the straight edge of the pattern that represents the vertical plane of the forward bulkhead onto the 4 foot edge of the plywood. Refer to sheet 2/8 of the building plans, Plywood Layout Sketch, to plan and layout the pieces to reduce waste. Make sure the paper pattern is laid out flat and smooth on the plywood. Use an awl to pierce tiny holes through the pattern to locate the points that will create the shape of the forward web. After the points have been plotted out, lift the paper and using a batten connect the points by bending the batten around the various awl holes. After the builder is satisfied with the transfer of the pattern onto the plywood cut the piece out using a saber saw (in some circles referred to as a hand jig saw). Note: always cut to the outside of the line you are following, leaving the line remaining on the piece you are saving. After the piece is cut out any excess amount of wood may be removed with a sure-form tool, shaving the wood down to the line in a controlled manner. After the piece is cut out, place the piece on top of the paper pattern to check for accuracy. The after spine is cut out in the same fashion. The forward web and after spine are sandwiched between pieces of western red cedar outlining them to give strength and to keep the pieces from oil canning under any load. The overall thickness of the forward web and after spine can not exceed 30 mm so the two pieces of western red cedar that will be used to outline them should be 13 mm square. It is a good practice that the entire unit is clamped onto a solid flat surface such as a bench top covered with foil so the epoxy will not adhere to the bench top while these support pieces are glued onto the main piece. After the epoxy is set the clamps can be removed and the foil and stray drips discarded. By doing this there is no way the builder will accidentally introduce a warp or unwanted bend into the piece. It should be noted at this time that we are using the West System brand of epoxy and the supporting products advertised for their product. The Gougeon Brothers have assembled a Technical Manual to their products and in the manual there is a complete guide on how to use the West System and the supporting products. Throughout this building instruction we will assume the reader has become familiar with this information. The Technical Manual is free for the asking from the Gougeon Brothers and there are several other related manuals that are available from them that the builder may find useful. We do recognize that there are several good epoxy products that are in use throughout the world and we do not endorse one product over another and have no interest in doing so, therefore we will assume the reader will become familiar with the selected bonding agents proper usage. The centerboard well is a slightly more complex piece to assemble then the forward web or after spine. The sides of the centerboard well are two identical pieces cut from 6 mm plywood. These make up the profile of the centerboard well. The best way to cut matched pairs is to clamp two pieces of plywood together and cut the pieces out at the same time. The two pieces are then fitted with solid 18 mm mahogany caps and 18 mm square mahogany case logs along the rocker curve. The centerboard that is going to be used in the boat is 29 mm thick so the centerboard well slot is going to be 30 mm wide. This is the maximum width the slot can be, so be careful that you do not make the slot wider then 30 mm. The packing pieces that will be used to separate the centerboard well sides are made from western red cedar. We will glue two pieces of red cedar together to get a piece that is over sized in thickness and then use a surface planner to bring the piece down to the 30 mm thickness. Some builders recommend that the interior sides of the centerboard well be lined with a high pressure type laminate such as Formica or Wilsonart. This material might be called by a variety of different names usually associated with the manufacturer’s name as in the case with Formica. Regardless of what it may be called it is all the same product, a high pressure paper laminate. Although it is used in the manufacturing of countertops it is NOT waterproof and can delaminate with constant exposure to moisture. Although this product does provide a good surface for the centerboard to slide against initially, it is our recommendation the builder not use this material as once it starts to delaminate it will absorb water and swell. It becomes a source of weight in the boat, eventually deteriorates and falls apart. A better alternative is to coat the interior sides with a mixture of epoxy and graphite powder, West System Additive no. 423 or similar product. After all the pieces are assembled and the epoxy/graphite finish is placed on the interior surfaces, the case is ready to be assembled. To assemble the case place the unit onto the building form and locate the position of the centerboard well along the rocker curve. Fabricate three 90 degree blocks of wood that are as tall as the centerboard case is wide. Locate the B, C, and D stations on the rocker curve and using 3 inch long deck screws anchor the blocks down to the building form to create a vertical surface 90 degrees to the building form’s surface at each measurement station. 18 mm thick scrap blocking is placed under the bottom centerboard case side to keep the centerboard case parallel to the building form surface. When the builder is satisfied that the pieces line up correctly and the rocker curve on the centerboard well matches the rocker curve on the building form, clamp the unit to the 90 degree blocks and pre-drill several 1/8 holes into the sides of the centerboard well in the packing area to locate temporary 1 inch no. 8 sheet metal screws. It is a good idea to coat these screws with Vaseline or wax as epoxy has a tendency to adhere these screws in place. Once the builder is satisfied with the dry clamping of the unit, separate the unit and assemble it again, this time using epoxy to bond the pieces together. Next clamp the well unit onto the 90 degree blocks so the unit can not move from the established rocker curve and allow to cure for 24 hours. After the centerboard well is assembled and the forward web and after spine are outlined with the solid lumber pieces the whole center support unit is ready for final assembly. The forward web is fitted into the forward slot located in front of the mast step area of the well unit. The after spine will slip into the slot at the after end of the well unit. All three pieces will be placed on the building form and blocked up in such a way that the forward web and after spine are in perfect line with the center of the centerboard well. Locate all the measurement stations for the rocker on the building platform. Screw 90 degree blocks down to the platform to create vertical surfaces located at the measurement points onto which the three pieces will be clamped to while the epoxy that bonds them together cures. Before proceeding to glue them together you will need seven blocks to establish the rocker curve, a block to represent the after transom and a block to represent the forward transom. Make sure the blocks line up with the rocker curve at the point of measurement and the transom blocks are placed in such a way the over-all length of the boat is represented accurately. In addition to the rocker curve points, there are three points that should be carefully laid out to form a datum line from the after spine, the top of the centerboard case and the point where the forward transom meets the rocker curve on the forward web. The three pieces should be placed to fit into the rocker curve and create this straight line across the top of the centerboard case. Once the builder is satisfied the positioning of the pieces is correct they should be clamped onto the building form at the 90 degree blocks to hold them securely in place as temporary 1 ½ no 8 sheet metal screws are secured through the centerboard well into the forward web and after spine. Again, these screws should have some type of lubrication applied to them. Once the builder is satisfied that the dry clamping is correct and accurate, disassemble the unit and apply the epoxy to the joint area and re-assemble. Take extra time to check then re-check that the rocker is lined up correctly and the over-all length of the boat is correct. The last check should be to line up the three points that form the datum line across the top of the centerboard well and make sure these form a straight line using a chalk string. Once all the checking is complete leave the whole unit sit undisturbed for 24 hours to allow the epoxy to cure. After the epoxy is cured the unit is ready to sit upside down on the building form and the first of several measurements will be conducted to assure the boat will pass the measurer.
© Fireball International, 2003
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