Rudder laminate design
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adapted from the Antrim/Pineapple sails method available at: http://www.well.com/user/pk/PCrudder.html (Except rudder force -A6thru A12- is based on Dave Gerr's "Elements of Boat Strength".)
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Fill in the yellow cells!
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9Design speed, the fastest your boat will be moving when you deflect the rudder "hard over", in knots
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3Underwater surface area of the rudder, in s.f.
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833 = Total pressure (force) on rudder, pounds
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3.5Horiz. distance gudgeon CL to center of pressure (CP) of rudder, inches. (assume CP @ 35% aft of LE)
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18Vert. distance from lower gudgeon to centroid/center of pressure of rudder, inches.
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14,991bending moment, in.-lbs.
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2,915twisting moment, in.-lbs.
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15,272combined moment, in.-lbs.
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3Safety factor, between 2 and 4 suggested
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100000Design stress of laminate, from 10,000 for fiberglass cloth, to 100,000 for carbon with uni fibers. psi
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0.458Required Section Modulus, in^30.458
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Marko:
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10Width of blade, inches.10
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1.2Design thickness of blade, inches1.50
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1.069Core thickness, inches1.395
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0.066Skin thickness required, inches (at lower gudgeon/point of max bending)0.050
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36Total fiber ounces per yard to achieve skin thickness28953g/sqm
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Gudgeon load calcs
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10Distance between gudgeons,inches10
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1,499Force on upper gudgeon, pounds7kN
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2,332Force on lower gudgeon, pounds10kN
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0.25418-8 hardened stainless pin diameter, inches (loaded in single shear)6.455mm
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Note: grounding loads or impact loads are not considered, nor is "hoop" or compression
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strength to resist pintle strap loading. These calculations are not my own, although they
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appear to match real world experience. USE AT YOUR OWN RISK!!!
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