2-34 BOAT HULL DESIGN 



The horizontal load is 210 pounds, and the distance between the mast partner and thwart 

 is about 4 ft. 6 in. Following the same procedure as for the gunwale for the rowboat: 



Bending Moment, M = ii = " xu , x - u = 28^0 in. -lbs. (2.7) 



h h 



Factor of Safety = 2.0 



Ultimate Stress of Hat in Tension, F tu = 11,000 psi (Table 5-6) * 



.-,-, ,-, „ .-, c . Ultimate Stress „ F+ u in q \ 



Allowable Tensile Stress = — ; f, = bu vz.sa; 



Factor of Safety x,u F.S. 



v 11000 rtr . n _ 



*tu = 5500 psi 



Reauired Section Modulus = Bending Moment . ,, = K_ (2>8a) 



Allowable Stress f^ 



_ 2oU0 _ n <lC . ^ 

 Section Fodulus of Gunwale, Figure 2-21, Z = 1.568 in.- 5 Satisfactory 



* For an explanation of the use of tensile rather than flexural stress, 

 see Design Example 2-1, gunwale and thwart design. 



Finally, a check must be made of the shear loading on the horizontal web of the gunwale. 

 Consider the horizontal load of 210 pounds to be applied by the bracket to the web. 



ultimate Shear Stress of Woven Roving, Y sv = 7500 psi (Table 5-14) 

 Factor of Safety = 2.0 

 Allowable Shear Stress, f s = 3750 psi 

 Area = Thickness of Laminate x depth of gunwale x 2 

 A = 0.113 x lj.0 x 2 = 0.90.'i in. 2 ' 



Stress, f c = £ (2. 18) 



A 



f = £i2 — = 232 psi Satisfactory 

 3 0.90. ! i 



Mast Support: The mast is subjected to loading from two sources. Loads in the hori- 

 zontal plane from the sail and boom, and vertical and horizontal loads applied by the stays. 

 The stay loads are of two types; the forestay being loaded primarily by the jib and the side 

 stay being loaded by the horizontal load at the top of the mast. 



The mast is supported by the mast step at the bottom of the hull which resists the 

 vertical compression in the mast, and also by the mast partner which is a horizontal 

 support reducing transverse bending in the mast. The horizontal load at the mast partner 



