Boating NZ : FREE TO READ April 2014
54 Boating New Zealand April 2014 In powerboat design, the size, angle and placement of spray rails, chines and strakes have significant influence in how the boat performs, along with deadrise, beam and longitudinal centre of gravity, as covered last month. FUTURE CONCEPTS CHRISTIAN STIMSON 54 T he key variables available to a designer are deadrise angle – ie, the amount of vee in the bottom, beam at the chines and LCG (longitudinal centre of gravity) position. Plugging these into the software will output the required horsepower for a given speed, the running trim at that speed and whether the boat demonstrates dynamic instability in pitch – known as porpoising – as well as a few other useful numbers. Varying deadrise at the design stage is one way to adjust the position of the Longitudinal Centre of Pressure (LCP or centre of lift) to align it with the Longitudinal Centre of Gravity (LCG) to attain a target trim angle. Conversely the designer can try to move the LCG to align with the LCP that the optimum hull form generates. VICES AND VIRTUES When designing a powerboat, some aspects are locked-in due to constraints such as the accommodation layout and engine installation (Rule Three – see opposite page, top) which all affect the LCG. Depending on the basic hull concept, the designer has various tricks to counter these, for example locating the fuel tanks at the LCG so that the trim is barely affected by the reduced load as fuel is burned. TO THE HULL POWER Part II TheTristram 741 has waterline strakes with mostly horizontal spray rails parallel to the waterline. REGULAR_Future concepts_April14.indd 54 19/03/2014 1:06:51 p.m.
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