The perpendicular line intersecting AB and C intersects the extension line of AB at D, ∠CAB+∠ACD=90? ; So ∠ ACD = 42;

According to known available ∠ACB=36? ; So BCD = 6? ;

Sin∠BCD=BD/BC, then BD=54*Sin6? ;

Cos∠BCD=CD/BC, then CD=54*Cos6? ;

Tan∠ACD=AD/CD=(AB+BD)/CD

So CD*tan∠ACD-BD=AB=54*Cos6? *tan42？ -54*Sin6？

=54*Sin(2*42？ )sin42？ /cos42？ -54*cos(2*42？ )

=54*2sin42？ cos42？ sin42？ /cos42？ -54*[ 1-2(sin42？ )^2]

=54*2(sin42？ )^2-54+54*2(sin42？ )^2

=2 16*(sin42？ )^2-54

Ship speed =AB/2 hours