"First, let's finish the ship that will house this engine!"
Marcia's energetic voice rang through the workshop.
In front of her sat the prototype Golem Engine Jin had crafted.
It was destined for a six-meter trimaran—a prototype boat designed to be marketed for its high speed, maneuverability, and stability.
The installation and final adjustments took three days. With the work complete, they immediately moved to the trial run.
The crew consisted of the usual pair: Marcia at the helm and Arrow acting as her assistant.
"Be careful, Marcia."
"I know, Dad."
The memory of her father, Rodrigo, acting recklessly and suffering serious injuries while searching for her after a Bowall destroyed her ship was still fresh in her mind. For his sake, she was determined to return safely.
The trimaran pulled away from the pier at a slow crawl. It glided smoothly out from the calm waters of the bay where the dock was situated.
"Right, the ship's stability is unchanged... Well, that's a given."
The engine was roughly thirty percent heavier than the previous model, but since they had accounted for that during the design phase, the vessel's overall balance remained perfect.
About thirty minutes later, they cleared the bay, and the waves grew slightly taller.
"Alright, Arrow, here we go!"
"Yes, Marcia-sama."
With a quick word to her assistant, Marcia opened up the engine.
She used a foot pedal to control the output. As she depressed it, the flow of mana into the engine increased, raising both its RPM and its output.
"Whoa! This is incredible!"
Marcia felt a surge of acceleration unlike anything she had experienced with previous engines.
"Jin mentioned it has about four times the horsepower, didn't he?"
In this context, "horsepower" referred to the amount of work the engine could perform. Generally, horsepower is the product of torque and RPM.
To increase the speed, Jin had halved the stroke of the pistons, which doubled the RPM but halved the torque. He had also reduced the size of each cylinder to make the unit compact, which halved the torque again.
To compensate for this drop, he had combined eight cylinders into a single horizontally opposed unit. Since the original Golem Engines were single-cylinder, this multiplied the torque by eight.
By simple calculation: the RPM was doubled, and the torque was doubled (1/2 × 1/2 × 8 = 2). Since horsepower is RPM multiplied by torque, the final output was four times greater (2 × 2 = 4).
Furthermore, because Jin had personally crafted the prototype, its efficiency was about twenty percent higher than a standard build.
"Haha, it's so fast! This is exactly what I wanted!"
Marcia grinned, delighted by the performance that exceeded her wildest expectations.
"Marcia-sama, there is a reef ahead," Arrow warned.
In her excitement, Marcia had allowed the boat to draw dangerously close to a rocky stretch of water.
"Right, slowing down!"
However...
"Wait, what!?"
The trimaran had gained so much momentum that it didn't decelerate nearly as quickly as she expected.
"Evasive maneuvers!"
Marcia yanked the control stick with everything she had, narrowly clearing the rocks by a hair's breadth. If she hadn't been piloting a stable trimaran, the vessel might have capsized from the sharp turn.
"That... that was close..."
Marcia realized that while the new engine provided immense speed, it made slowing the vessel down significantly harder.
"This is a serious problem..."
She brooded over the issue on the return trip.
"I could ask Jin... No, I have to solve this myself."
As the wharf and the workshop came into view, she made her resolve clear.
"I shall assist you, Marcia-sama," Arrow said, nodding firmly in support.
"That's a tricky one."
"Isn't it?"
That night, Marcia and Rodrigo sat across from each other, deep in discussion.
"I think reversing the screw's rotation would be the most effective method," Rodrigo suggested.
"But that isn't a feature of this engine. I'm sure Jin could add it in a heartbeat if I asked, but I want to keep that as a last resort."
"In that case, hmm..."
The discussion continued late into the night.
"Alright, I've got it!"
By midnight, they had decided to test a type of brake that extended plates directly into the water. The principle was the same as the air brakes used on jet aircraft.
The first prototype was a bit clunky, but the fact that Marcia and Rodrigo had arrived at the solution independently spoke volumes of their talent. They dubbed it the "Water Brake."
Before setting out the next day in the modified trimaran, they performed a full mechanical check.
"Marcia-sama, the engine's bearings are showing slight signs of wear," Arrow reported.
This was exactly what Jin had told Arrow to keep an eye on.
"If we continue using it like this, play will develop in the shaft. I estimate efficiency will drop to seventy percent within ten days."
"It's not an immediate problem for today, though, right? Then we'll look into it once we get back."
Marcia decided to tackle their problems one at a time.
"Yes! It works!"
Marcia cheered as she tested the brakes at sea. The plates, extending into the water—which offered far more resistance than air—successfully brought the speeding vessel to a halt.
"...So the increased engine power is the culprit."
Upon receiving Marcia's report, Jin sat back and pondered the bearing wear. Since this was a flaw in the engine itself, it was only natural for Marcia to ask the supplier for an improvement.
The current bearings were made of gunmetal, an alloy of copper and tin. Because gunmetal was softer than the iron-alloy crankshaft, it naturally wore down over time. Conversely, if the bearings were harder than the crankshaft, the shaft itself would be damaged.
"Lubrication is one option..." Jin muttered.
Proper lubrication involved creating a film of oil between the shaft and the bearing to prevent direct contact, reducing both friction and wear.
"Or I could use a low-friction material..."
Ground Spider resin, or GSP, was made from the silk of ground spiders. In terms of modern Earth materials, it was comparable to Teflon, polyamide, or polyacetal—substances with extremely low friction coefficients that resisted fouling.
"It would be the perfect choice for the bearings."
However, Jin was hesitant to use a material that could only be found on Hourai Island.
"I need something else..."
"My Lord, what if you used the fins of a Death Sea Serpent?" Laojun suggested.
"Oh, right. We do have those."
Jin and Reiko had once hunted fifty Death Sea Serpents off Io Island, and the bounty from that hunt had been distributed to Port Rock Town as well. Since Death Sea Serpent fins were a known commodity in general circulation, using them wouldn't raise any eyebrows.
"Yeah, this should be more than durable enough."
While the fins weren't quite on the level of GSP, their friction coefficient was remarkably low, making them an excellent material for bearings.
With this final adjustment, the horizontally opposed eight-cylinder engine Jin developed became virtually maintenance-free, becoming the new flagship product of the Marcia Workshop.