You need to be sure if the quoted power includes (SHP) or excludes (BHP) transmission losses. Although this is less likely to matter in a boat, than a car.
pk is Dutch paardekracht equals the German Pferdestärke (PS)
Handy conversion chart
To convert from: To: Multiply by:
BHP PS 1.01387
BHP Ft Lbs/second 550
BHP Watts 745.7
PS Kg M/second 75
PS Ft Lbs/second 542.476
PS Watts 735.5
Kilowatts BHP 1.341
Kilowatts PS 1.360
Lb Ft Nm 1.356
courtesy of those nice people at Puma Race engines