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Wide-bow hull As stated earlier, the Fireball can be built by following one of two similar but different designs. Although the boat will have to be measured according to the rule book, with 121 points of measurement to take into consideration, a builder can alter the non-measured areas of the boat in the bow compartment and create a boat with a distinctive wide bow. This wide bow configuration is seen as an advantage in certain wind and water conditions. Basically when the wind reaches about 12-14 mph, and when the waves start to white cap, this shape will handle in a more responsive manner than the standard bow design. Most commercial builders follow this wide bow design so we will build our boat according to this design philosophy. Two things go into making the wide bow design work. First, the rocker curve must become flatter. There are seven points of measurement that determine the rocker curve of a Fireball. The first and seventh points are exact measurements with no tolerance allowed. The middle five points can be altered by as much as 8 mm and still be within tolerance of the rules. To understand how we will flatten the rocker curve, we will explain how the curve will be measured on a completed boat. The boat will be placed upside down and the first point will be located in plane with the after transom 305 mm above the hull. Measure along the curve of the rocker to a point 4760 mm from the after transom where the seventh point is located 407 mm above that station. A string will be stretched between these two points to form the datum. Now measure from the transom, along the curve 765 mm to locate station A; 1580 mm to locate station B; 2390 mm to locate station C; 3208 mm to locate station D; and 3975 mm to locate station E. At station A the distance from the bottom of the boat to the string should be 231 mm. At station B the distance should be 164 mm. At station C the distance should be 125. At station D the distance should be 137 mm. At station E the distance should be 229 mm. Each of the prior measurements have a tolerance of plus or minus 8 mm so, for an example, at station A any measurement between 223 and 239 mm is acceptable according to the rules. What we will do is to deliberately alter the measurement at certain stations but the curve will still have to fall within the stated tolerances of the rules. With the boat upside down at stations A through D we will push the measurement down toward the hull by 5 mm. At station E we will pull the measurement away from the hull by 5 mm. The result will be a flatter curve then the planned curve the rules intend for, yet the curve will still be a legal one. We will loft our plans according to these points. The forward web, centerboard well, and after spine will be cut and assembled using these points to create the rocker curve. But this alone will not determine a wide bow shape. One more alteration will have to happen to create the wide bow design. The section of the boat between the forward bulkhead and the front transom must be widened to add more volume in the forward area. To create this we will be adding ring frames to the forward area of the boat, which is a non-measured area of the boat. If you will refer to the rule book under section 9.11, hull sections, you will see the different points of measurements to which a typical hull section will be measure to. This typical section is a basic shape that runs the entire length of the boat but is only measured at four stations. These measured stations are located at the after transom, 765 mm from the after transom, 3208 from the after transom and at the bow transom. The width of the hull section at these stations, if looked down on, will give the builder the over-all shape of the boat. The area of interest for the wide bow hull is the forward tank area from the 3208 station to the bow transom. This area is a non-measured area and can be altered as long as the resulting curve created by bending a batten around the four measured stations results in a fair curve. The basic definition of a fair curve is one with no flat spots along it. We will be interested in altering the "D" dimension of the non-measured area of the hull section located approximately 90 mm in front of the forward bulkhead. We want to push this dimension out as wide as possible and still maintain a fair curve. To create this shape make the following alterations at the measurement stations located at 765 mm and 3208 mm from the after transom At the 765 mm station, alter the following four dimensions: Dimension A will be altered from 1206 to 1211 Dimension C will be altered from 390 to 385 Dimension D will be altered from 1146 to 1151 Dimension E will be altered from 119 to 114 At the 3208 mm station, alter the following four dimensions: Dimension A will be altered from 1225 to 1230 Dimension C will be altered from 375 to 370 Dimension D will be altered from 1143 to 1148 Dimension E will be altered from 176 to 171 These dimensions represent the finished hull section with the skin panels in place, and the topcoats of paint applied. To complete the preparation of the wide bow procedure, construct a ring frame based on the sizes of the hull section at the 3208 station as stated by the rules. Do not alter this pattern. Dimensions A and D are the critical dimensions on this pattern. Dimension C will have to conform to the shape of the bottom panel so it will alter naturally. Dimension E will alter naturally as well as it will be controlled by the topside panel at that station. Dimension A and D represent the maximum width of the section and we want to carry that width as far forward as possible and maintain a fair curve. If during the lofting process the builder notices that the curve becomes flat, the rule has become violated and the boat will not be legal. To fix this the ring frame should be reduced in width to allow a fair curve to happen. This is noted as not all woods bend in the same fashion. Two pieces of western red cedar should, in theory, bend the same amount over the same distance but due to internal stresses and variations in densities, they will not bend exactly the same, altering the fair curve slightly. The wide bow design is a total design concept based on the alteration of specific hull sections. The altered hull sections, along with the flatter rocker curve, is what gives the wide bow design a performance advantage in the previously stated wind and water conditions. The tolerances for building a Fireball are very small. By altering the recommended sizes as outlined the builder will reduce the allowed tolerances by more then half the amount that would be allowed if the builder were to construct a standard shape hull. The builder should be aware of the reduction of the tolerance and be careful to make sure that all measurement points are checked accurately to insure the boat will pass the measurer’s examination. The rocker curve and the hull sections are the first items on the boat measured. These are the items that determine the shape of the hull. All other measurement points fall within this shape so if these items are incorrect, they can usually be corrected with little trouble. The basic shape of the hull must measure correctly as all other measurement points are taken from that shape. For this reason we will be building the hull on what we refer to as a building form.
© Fireball International, 2003
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