One Piece does a good job of incorporating science into its expansive lore. Its gadgets and inventions have some scientific ground but are still largely cartoonish. That being said, the series has a slew of inventions, and the Straw Hat Pirates have seen their fair share of them as well. This is mostly because they have one of the best and whackiest shipwrights in their midst.
Franky has been building warships and weapons ever since he worked under the late Tom. Despite being a child at the time, his creations were destructive enough to pose a threat. They were unfortunately strong enough to wreak havoc on an island, framing him as a bad guy. However, he has created better inventions since then, and they are undeniably grander both in scale and function. Here are the strongest among them and what exactly they can do.
His Body
After wrecking his body in a bid to stop the sea train that took his adoptive father away, Franky used his engineering skills to save his life and construct a cyborg body. However, he was only able to do the front part, as he couldn't reach his back. He managed to install various mechanisms in his body such as rockets, an extendable metal arm, an air compressor and even a cola refrigerator on his stomach, which was very essential as it powered his strongest attacks.
He further modified his body during the two years the Straw Hat Pirates were separated. Dr. Vegapunk's futuristic designs and a fully-stocked abandoned laboratory greatly helped the mad cyborg complete his construction spree. When he was done, he was able to shoot laser beams from his palms, launch explosive missiles, breathe fireballs, draw an extensive amount of artillery with ease and light up his nipples.
General Franky
Franky didn't just modify his body in the lab; he also created a gigantic robot -- General Franky. This is a one-person vehicle that's formed by fusing Kurosai FR-U IV, the motorcycle-esque vehicle Franky usually uses, with Brachio Tank V, the tank Usopp usually pilots. General Franky also has a giant sword called Franken, but it's usually used in vain, as Franky has little to no swordsmanship training.
General Franky initially came off as pointless, as it only seemed to offer a bigger shell. It used only Franky's weapons when it made its debut, but it showed its full inventory as the series went on. It turned out that it wasn't just a gag after all -- General Franky has a very durable body that was able to withstand being shot by a rocket at point-blank range. It also has stronger artillery compared to Franky's already powerful arsenal. Further, it may have some sort of filtering system, as it was able to shelter and allow Franky to roam within Caesar's poison gas.
Thousand Sunny
The Thousand Sunny is the Straw Hat Pirates' second and current ship. It's made from Adam Wood, a wood of legends, and contains everything each member wished to be included in their new ship. It also has multiple features that no other ship has in the world of One Piece. One of its features is the Soldier Dock System, which is comprised of six different compartments containing devices for the Straw Hats to use.
Thousand Sunny also has a unique cola-powered maneuver system, the Coup de Burst. It's similar to Franky's Coup de Vent but is mostly used to escape the ship's pursuers. The lion figurehead likewise has multiple features. It can spin like a propeller, allowing the ship to move backward, but even better is the Gaon Cannon that's hidden within the mane. This blasts compressed air forward in exchange for using three barrels of cola.