Fin No. 2s, having the smallest plan area, shows reductions comparable to Fin No. 2. On 

 the other hand, Fin No. 4, having the largest plan area, does not show any added improvement. 



In establishing the geometry of the fins, one must take into account the vorticity 

 generated by their motion. This arises from the pressure differences between the upper and 

 the lower surfaces of the fin. Such vorticity can result in structural damage, such as recently 

 experienced by a Dutch liner. 



It appears from observations during the tests that the severity of the hydrodynamic 

 loading imposed on the hull by the vortices shed by the fins can be lessened by: 



1. Deeper submergence of the fins (Fin No. 4). 



2. Greater fin span (Fin No. 1). 



3. Tip fences. 



4. Relief mechanisms such as slots and holes (Fins No. 2, 4, 2A, and ih). 



To provide a basis for structural design, hydrodynamic bending moments were measured 

 at one point along the span (Fin No. 1) corresponding to 7 feet off the centerline, full scale. 

 These are shown in Figure 15 as a function of ship speed, wave length, and wave height. 



In regard to the strength of the fins, the bending moments presented in Figure 14 should 

 be treated with caution. Since the load distribution is unknown, it is not possible to derive 

 the values for the bending moment at the root. Theoretical slamming computations, however, 

 indicate that the bending moment due to slamming is higher than that predicted for the quasi- 

 steady state. Thus, the structural design of the fin should be based on loads experienced 

 during slamming. The dihedral fin was observed to be the smoothest of the various configu- 

 rations tested in respect to re-entering after emergence in the most severe wave conditions 

 tested. 



CONCLUSIONS 



The results of the model tests indicate that reduction of the pitching motion of the 

 Mariner ship can be obtained by means of fixed antipitching fins installed at the bow. 



REFERENCES 



1. Pournaras, U.A., "Pitch Reduction with Fixed Bow Fins on a Model of the Series 60, 

 0.60 Block Coefficient," David Taylor Model Basin Report 1061 (Oct 1956). 



2. Szebehely, V.G., "Apparent Pitching Axis," Forschungshefte fur Schiffstechnik, 

 Vol. 3, No. 16, p. 184 (1956). 



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