To destroy structures with a Motor Boat or a Motor Boat Rocket in Fortnite Chapter 3 Season 1, you need to find a Motor Boat first. The best place to find Motor Boats in Fortnite Chapter 3 Season 1 is in the lagoon on the east side of the map. There is a particularly high concentration of Motor Boats south of Mighty Monument. There are motorboats dotted around the coast and in several lakes and rivers as well. The map below shows all Motorboat locations in Fortnite Chapter 3 Season 1. Some of the locations marked here have multiple Motor Boats.
When you find Motor Boats, the first thing you need to remember is that the control of land vehicles is different from that of land vehicles. The button functions as a car booster, firing rockets in a Motor Boat. The motion controls of a boat are actually quite similar to those you’d use on land, just you have more inertia.
The definition of “structure” in the Power Boat demolition mission is rather loose. Basically anything man-made and destructible is considered a structure, so it consists of small objects like boxes and crates. It’s best to destroy everything using rockets as most of the structures are on land, and if you try to destroy them by ramming them with a Motor Boat, you’ll probably run aground.
https://www.gamepur.com/guides/all-motorboat-locations-in-fortnite-chapter-3-season-1 All Motorboat locations in Fortnite Chapter 3 Season 1