Span uses the IMS nomenclature for its measurements. All measurements are taken from the position of the headstay base. Since Span does not take yaw wind moments into account, the position to the headstay is irrelevant for the performance prediction. Also see: Rig Measurement Definitions on page 30 for more information on the position of the headstay.
For a more detailed discussion of the hull parameters calculated by SPAN, interested readers are referred to: (A)IMS – an Almost Ideal Measurement System, by David Pedrick, presented at Yacht Vision '94, Auckland, New Zealand, 16-20 Feb. 1994.
Back to Entering Data
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Aft girth station |
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Design waterline |
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Forward girth station |
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Longitudinal position of maximum hull beam. |
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Vertical centre of gravity |
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Freeboard (Vertical distance from the water to the sheerline) at the forward freeboard measurement station. |
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Freeboard at the aft freeboard measurement station. |
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Righting moment at heel angles of 2, 20 and 40 degrees divided by the heel angle in degrees. |
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Maximum beam at sheerline |
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Propeller Installation Projection Area represents the equivalent flat plate area of the prop installation used to calculate its drag at various speeds. |
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Depth attenuated maximum sectional area. Used to calculate the effect of the hull on the keels ability to generate lift. |
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An adjusted beam to depth ratio. A measure of the fineness of the hull which has an effect on added resistance due to heeling. |
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Loaded draft; somewhat deeper than measurement draft. |
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The vertical difference between board up and board down draft. |
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The draft adjusted for hull / keel interaction and end-plate effects and derived from B, below. |
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An integrated value of hull width, using a "second moment" approach and a depth attenuation factor. |
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Wetted surface area of the hull and appendages. |
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Displacement in sailing trim |
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Effective hull lengths of the yacht under different conditions of displacement and heel. These values are derived from the sectional area curve. L is the effective sailing length used to calculate the hull resistance. |
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Maximum crew weight |