## LP Calculator

Area = 244.28

LP = 12.16

Sail is a 90.1 percent sail

The depth causes the sail to go back only 98.3 percent of its length

so the foot will only measure 12.78 under sail

Angle of sail at tack is 69.3 degrees

Clew height is = 1.52 (requires head stay angle)

NOTE: To find the Headstay angle, pick a point on your boat back from the tack about where the clew will be and measure the distance from there to the tack, from there to a point up the head stay, and from that point on the head stay down to the tack. Enter those numbers into the LP calculator as the foot, leech,and luff dimensions. The resulting angle at the tack will be the head stay angle. If the sail is near 100% or if the deck is flat, you can use I, J, and head stay length to calculate the head stay angle.

This page calculates the area of the triangle given the three sides then calculates the LP by solving the equation area = 1/2 * LP * luff. The initial area calculation uses Heron's formula that says the area of a triangle abc is SQRT ( s * (s - a) * (s - b) * (s - c) ) where s = 1/2 (a + b + c). The final calculation is the perenct of LP to J. NOTE: An actual measurement of a real sail will probably give a different result as this calculation does not try and predict luff hollow. If the luff hollow at the LP is known, it could be substracted from the calculated LP. This might change the result by a small amount.

The ratio of the chord to the arc is calculated by first calculating the radius of an arc segment with a unit chord length by solving the formula r^2 = (1/2) ^ 2 + ( r - h) ^ 2 where h is the depth fraction.

The arc lenght is given by 2 * r * atan ( (1/2) / (r - h)) and the shortening is 1/arc.

Headstay angle is the foot length times the sin of the difference between the headstay angle and the sail's clew angle.

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Disclaimer: The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with L-36.com. I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerious of sources and is presented automatically. It is not checked for accuracy either by anyone at L-36.com or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program. |