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Investigation of the Effectiveness of an Antipitching Fin and Fin Strut Combination on the Mariner

The presence of an anti pitching fin attached at the hull 
basel ine is known to cause severe hull vibrat ions. Two conditions 
thought to contribute to this problem are the col lapse of the de- 
formed wave surface profile above the fin and by fin re-entry after 
a bow fin emergence. An experimental investigat ion was conducted 
to determine the effect of increased strut length in reducing these 
conditions on a MARINER rnodel equipped with an anti pitching bow 
fin. Analytical predictions were also made to determine the 
effectiveness of a bow fin in reduc ing the pitching motion of the 
MARINER hull in a seaway. The anti pitching fin used in the MARI NER 
experimental investigation was a flat plate with a geornetric aspect 
ratio equal to that of the flat plate fin used in earl ier work by 
Ochi. The effect of foil shaped struts of different lengths, to 
increase the vertical separation between the fin and the keel of 
the mdel at the bow, was experimental ly evaluated in regular waves. 
Vi sual observat ions (video coverage) of the experimental investi- 
gat ion indicated: (l) the reduction in size and number of wave 
surface profile deformations for some of the wave conditions in- 
vest i gated, and (2) the Obv ious reduction of fin emergences, with 
increasing strut length. The reduct ion in the pitching ion 
resulting from the addition Of the bow fin to the MARINER hull, 
as is indicated by the ana lyt iCal invest igat ion, is not cons idered 
significant as the mot ion is not excess ive without the anti- 
pitching fin.

As part of a program to evaluate the effectiveness of increased strut 
length 'n reducing antipitching fin- induced hull vibrat ions, an experimental 
investigation was conducted using an exist ing MARINER model. To determine 
the effectiveness of a bow fin in reducing the pitching an analytical 
investigation was made for the MARINER hull form in various long-crested 
irregular head waves with and w' thout the fin for comparison.