KPT1800A-WAP is the model code for the 2021 255 FSH SPORT E. Yamaha covers it in service manual LIT-18616-04-23.
That book serves the 252 FSH SPORT as well, and its coverage runs across the 2021, 2022 and 2023 model years. The two boats are close enough mechanically that the factory saw no reason to write the engine and propulsion chapters twice.
Contents follow the systems: periodic maintenance, engine service, jet propulsion unit, hull and deck hardware, steering and controls, electrical. Torque specifications, clearances and service limits sit with the procedures that need them, and the wiring diagrams are the full factory drawings. Diagnosis is organised by symptom, which is how a fault actually arrives.
Before ordering parts, check KPT1800A-WAP against the certification plate. On a fishing boat that may have changed hands, the code is worth more than the model badge.
