BOAT HULL DESIGN 



2-21 



Transom: The vast majority of fiberglass 

 boats built so far are powered by outboard 

 motors. Even rowboats and small sailboats 

 are generally arranged so that a small out- 

 board motor can be used as a means of pro- 

 pulsion. The transom must therefore, be de- 

 signed to support a motor of a size suitable 

 for the boat. The designer should always re- 

 member the trend toward ever increasing 

 power and size in outboard motors, and that 

 boat owners all too often use motors of higher 

 power than the designer considers necessary 

 or even safe. In estimating the horsepower to 

 be used in designing a transom the designer 

 should be generous, particularly for a stock 

 boat which will be widely distributed. 



LONGITUDINAL ST I FFENER SPACING 

 16 16 20 ; 



Vd~ 



.0100 .0140 .0180 .0220 

 REqUIRED SECTION MODULUS TO WOVEN ROVING FACE - INCHES 3 



PLIES OF WOVEN ROVING TYPE A LAMINATE 

 FACTOR OF SAFETY = 4 



Fig. 2-16. Bottom shell laminate 

 for fiberglass polyester cruising 

 sailboats based on current designs 



As a guide in selecting the transom thick- 

 ness and in determining the dimensions of the 

 area of increased thickness for the motor 

 clamps, minimum standards have been set up 

 by the Outboard Boating Club of America (14). 

 These standards call for a minimum transom 

 thickness of 1-3/8 inches for motors, totaling 40 horsepower and less, and 1-1/2 inches for 

 motors totaling more than 40 horsepower. The maximum thickness in way of the engine 

 clamping bracket is 1-3/4 inches for a single motor of 40 horsepower and less, and 2-1/4 

 inches for a single motor over 40 horsepower. In actual practice the entire transom is 

 sometimes made the thickness required in way of the engine clamping bracket. Alternatively, 

 the minimum thickness may be used throughout and steel plates added in way of the clamp- 

 ing bracket. 



The over-all dimensions for the area and the increased thickness are given in Table 

 2-1 below. 



TABLE 2-1 



DIMENSIONS OF MOTOR SUPPORT AREA 



CL OF MOTOR 



FORWARD FACE OF TRANSOM 

 LOOKING AFT 



AFT FACE OF TRAN50M 

 LOOK I NG FORWARD 



RE I NFORCED 

 AREA - 

 THI CKNESS 

 I NCREASED 



