"What's this? What are these?"
Marcia tilted her head at the components, which bore no resemblance to oars. Jin replied,
"Just watch. Reiko, help me assemble this."
"Yes, Big Brother."
While Reiko supported the heavy parts, Jin installed them onto the catamaran. Before long, the assembly was complete.
"There, it’s finished. Let's get it in the water to check the balance, then we’ll give it a trial run."
The device had been mounted to the rear of the catamaran's central hull.
At the very back sat a paddle wheel, and beside it was a circular wheel. This wheel featured a V-shaped groove with a belt made of flexible material wrapped around it.
The belt connected to another wheel positioned further forward.
From this forward wheel, L-shaped rods protruded on opposite sides, alternating in position. Slightly behind them was a seat, and slightly in front were handlebars.
It was exactly what it looked like: Jin had built a bicycle-style propulsion system where pedaling turned a paddle wheel—the sort of thing commonly found on pedal boats at tourist lakes and ponds.
However, seeing such a contraption for the first time, Marcia looked deeply skeptical.
"Can something like this really move a boat?"
"Proof is better than theory. Let's just try it out."
With the golem Arrow’s assistance, they launched the boat into the sea.
"Alright, I'll handle the steering. Reiko, you take the pedals."
"Eh? Is that going to be okay?"
Marcia still looked worried, but Jin simply gave her a smile.
"Yeah. Leave it to me."
"Fa... Big Brother, I am ready."
"Good. Let’s head out. We’ll start slow."
"Understood."
Reiko stepped on the pedals. The paddle wheel began to churn, pushing the water backward. The resulting reaction propelled the boat forward.
"Oh! It’s moving!"
Once the boat cleared the swimming area, it gradually began to pick up speed.
"Yeah, this isn't bad."
"Father, should I increase the speed further?"
"No, this is enough for now. Reiko, what’s the current ether converter output?"
"Yes. It is approximately five percent."
"I see. The efficiency is worse than I expected. I might need to adjust the shape of the paddle blades."
While still sitting in the pilot's seat, Jin used Forming. As long as there was physical contact, he could use the magic at a range of about three meters, though the efficiency dropped in inverse proportion to the distance.
"Oh, that seems a bit better."
After several fine adjustments, he managed to increase the projected speed by over thirty percent compared to their start.
"Alright, let's head back for now."
Jin performed a U-turn and guided the boat back to the dock. Marcia greeted them, her face lit up with excitement.
"Jin! That's incredible! You’re a genius!"
Jin felt a bit sheepish at the unrestrained praise, while Reiko looked on with pride.
"Just one more addition and it'll be complete."
"Is there still something missing?" Marcia asked.
"Yeah. The paddle wheel kicks up a lot of spray, so I want to add a cover to block it."
When the wheel spun at high speed, centrifugal force sent water flying in every direction, soaking both Reiko's and Jin's backs.
"If I do this... Forming. There, finished."
"In that case, can I try riding it?"
Seeing Marcia itching to get on board, Jin gave a wry smile.
"Sure. But before that, since you're the owner, Marcia, you should give this boat a name."
"Hmm? O-Oh, right. Well then... how about Cygnus?"
"Sounds good to me. Then, to match the name Cygnus... Surface Treatment."
"Huh? Wha-Whaaa?"
The hull of the catamaran transformed from its natural wood color to a pure white befitting its new name.
"W-What did you do!?"
"I just removed the pigment to make it white."
In essence, he had bleached it, though he had also applied waterproofing treatments in the process. Then, Jin turned his attention to the golem.
"Arrow, come here for a second. Good. Plating."
He used the nickel he had separated earlier when refining the bronze to plate Arrow's surface. This gave her a silver-gray finish and significantly increased her resistance to corrosion.
"T-That’s amazing! Jin, is it okay now? Can I go?"
Marcia looked like she couldn't wait another second, so Jin nodded.
"Yeah. Be careful out there."
"Alright! I'm off! Arrow, I'm counting on you!"
"YES. PLEASE LEAVE IT TO ME."
"Cygnus, launch!"
Because Marcia held the highest command authority, the coordination between her and Arrow was seamless from the start. Marcia immediately pushed the boat to its limits.
Kicking up spray from the stern, the boat glided across the water. Watching them go, Jin muttered to himself.
"Ah... as I thought, a paddle wheel really isn't the most efficient way to do this."
Reiko happened to overhear his self-criticism.
"Father, are you still dissatisfied even after that?"
Reiko possessed the knowledge passed down from the original Magi Craft Meister, Adriana Barbora Tsetse, but that knowledge contained nothing like the propulsion mechanism Jin had just created.
"Yeah. It's more efficient than oars since it doesn't involve reciprocating motion, but with that much spray being kicked up, well..."
To Jin, who held knowledge from modern Earth, the spray and waves were simply lost energy. He had wanted to use screw propulsion.
"But there are various problems with turning a screw..."
First, the direction of rotation would have to change ninety degrees from the pedals. Furthermore, he needed a higher rotation speed; a screw propeller is inefficient unless it spins rapidly.
"I can't make bevel gears yet..."
Currently, Jin was unable to produce gears. Since gears require two or more parts to mesh perfectly, they demanded extreme precision.
He had been able to make bearing balls because he only had to manage the weight and diameter, but gears involved modules, pitches, and involute curves—concepts that were currently beyond his manual reach.
"I’ll have to build machine tools first."
Having worked in a factory in his previous life, he had used lathes and milling machines and understood their general construction, but he simply hadn't had the time to replicate them yet.
"Well, I'll make that a future project for the laboratory."
After a while, the Cygnus returned, kicking up a rooster tail of water.
"Welcome back."
When Jin greeted her at the pier, an exhilarated Marcia cried out,
"Jin! This boat is incredible! I've never seen anything this fast!"
"I'm glad you liked it. So, was there anything that bothered you? Any complaints?"
When Jin asked, she replied,
"No, I have no complaints about the speed. It's the hull. I wish it could handle tight turns a bit better."
Because a catamaran consists of two long, narrow hulls, it has excellent straight-line stability but is inherently difficult to turn sharply.
"Hmm, but do you really need tight maneuvers for the race?"
"Well, no. Basically, we just leave the harbor, go around the island at the halfway point, and come back to the finish line."
"But," Marcia added with a grin, "there's nothing wrong with aiming for a better hull, right?"
Jin nodded in agreement.
"You're right. Progress stops the moment you become satisfied."
As the sun began to set and the wind died down, the group decided to finish their work for the day.