BOAT HULL DESIGN 2-35 



is relatively small and may be ignored. The vertical load may be approximated by assuming 

 the forestay and one of the side stays to be at the breaking point. 



Taking the vertical components of the 12 00 lbs. breaking load, the following vertical 

 loads are found: 



From the side stay, P s = ll80 lbs. 



From the forestay, F f = ll60 lbs. 



Total Ft = 23liO lbs. 



Considering the built-up nast sten to be of mat laminate: 



Ease of mast assumed 2 in. ;; 2 in. Mast rase periphery, L v = in. 



Compressive Stress, f c = c - a ° = iZ$ psi Satisfactory 



2x2 



p 



Shear Stress = =^ ; f s = — (2. 19) 



thickness of shell x mast base periphery t x Lp 



Use Factor of Safety = 2.0 



For discussion of Factor of Safety see chain plate support. 



Allowable Shear Stress, F s = 2222 = h?50 psi (Table 5-14) 



Required shear area, A s = QUO = 0.ii7 in. 



U950 



Minimum thickness of bottom of hull 



.h 



k specified and is satisfactory 



t = ' = .039 in. This is less than the shell thickness previously 



In order to avoid creation of local hard spots, see Chapter 3, the centerline stiffener 

 will be widened immediately under the base of the mat mast step. This extra width is 

 tapered off to the normal width to form a 12 in. wide reinforced area. 



The Mast Partner: The mast partner is made of the same scantlings as the thwart, 

 with a local increase in thickness to about 1/2 in. in way of the mast. 



DESIGN EXAMPLE 2-3. 19 FT. RUNABOUT 



This runabout is representative of the type of boat which has had the most widespread 

 application of fiberglass construction. It is intended for pleasure use, including day trips 

 in relatively open water, and for towing water skiers. The boat is somewhat larger than 

 the majority of its type, but the design principles illustrated are, of course, applicable 

 to the smaller sizes. 



Princ ipal Dimens ions - See Fig. 2-22 for details. 

 Length, Over -all: 19 ft. - in. 



