Judge Adeane said while Motley was the eldest of the three offenders, there was some suggestion he had been led by the other two in regard to the arsons at Splash Planet and the school.
The pirate ship had been valued at more than $300,000 and on top of that there were costs associated with removing the destroyed structure, the judge said.
There was some prospect of reparations being paid but it would be a long process.
Splash Planet's owner, the Hastings District Council, has previously said the pirate ship was insured for $354,000 and that it intended to replace the structure in some form.
A council spokeswoman said yesterday no decisions on replacing the ship had yet been made.
"The plan is to consult the public on ideas over summer - the facility manager has been tasked with [generating] a range of ideas to spark people's thinking."
The pirate ship was built in 1977, 10 years after the opening of Fantasyland, which became Splash Planet.
According to a police summary of facts, Motley and the other two youths had been at a party on April 5 when they made a plan to set fire to the pirate ship.
They cut a hole in a fence to get into Splash Planet and used petrol to start the fire. The pirate ship was reduced to a shell in its lakeside compound.
A member of the public raised the alarm by knocking on a nearby door and saying young people had been seen running from the area of the fire.
After serving his six-month community detention sentence, Motley faces a further 12 months of supervision.