The meeting on the following day, the 24th, began with a question from Rodrigo.
"Jin-dono, regarding yesterday’s explanation of the Wind Thruster... that used the wind magic ‘Wind,’ correct? Well, is it possible to make it treat—what was the term—water molecules the same way it treats air?"
While the question was a bit technically confused, Jin understood the intent behind it.
"In short, you’re asking if we can ensure the propulsion remains constant even if the thruster takes on water?"
"Yes, that! That’s exactly it!"
If a Wind Thruster were mounted to the side of the hull, it would inevitably suck in water when the waves grew rough. If the propulsion fluctuated every time that happened, the ship wouldn't be able to maintain a straight course, which would be particularly problematic during maneuvers like slow-speed ahead. That was Rodrigo's concern.
"...It might be possible."
Jin answered cautiously. If he responded too quickly, it would seem suspicious, and he didn't want them asking why he hadn't implemented such a feature from the start.
"Oh, truly! In case, Jin-dono, could I ask you to look into that improvement? the rest of us will continue reviewing the hull design."
"All right."
And so, Jin set to work on the Wind Thruster's improvements in a separate room. He wasn't entirely alone, as Reiko accompanied him.
Elsa watched Jin leave for the other room with a slightly disappointed look in her eyes.
"Father, is it really that difficult?" Reiko asked, looking puzzled.
Jin hushed her. "Shh, not so loud....An alteration like that can be done in two minutes. But you know, it’s not good to stand out too much by over-delivering, right?"
He seemed to be at least somewhat self-aware for once—though many might argue it was far too late for that.
"I understand."
Jin and Reiko then proceeded to partially dismantle the prototype Wind Thruster they had built the previous day. He sat before the components, lost in thought.
However, the subject of his thoughts was something else entirely.
"Even if they aren't geostationary satellites, if I bury markers on mountaintops, they could serve as landmarks... but I suppose people might just dig them up..."
"I believe that is quite likely," Reiko replied.
If a device emitted a strong magic signature, it would be easy to detect, making it an obvious target for the curious. That was why Jin remained fixated on satellites.
"Hmm, making something perfectly stationary relative to the ground is quite difficult..."
Maintaining a fixed position relative to the Earth's surface required incredibly precise calculations and accurate measurements.
"Hrmm..."
Jin wanted to establish landmarks not just for warp targets, but also to help aircraft and ships calculate their positions.
"Come to think of it, navigating a ship requires more than just a compass. What was it called... uh... was it a quadrant or a sextant...?"
To put it very simply, one could determine longitude using the time and the sun's position, and latitude by measuring the altitude of the North Star. If you knew both, you knew your location.
His thoughts were gradually shifting toward the science of navigation for the ship they were currently designing.
"Reiko, is there a North Star in this world too?"
Jin wasn't particularly knowledgeable about astronomy. Reiko contacted Laojun via her internal manacam to find the answer.
"Yes, Father. There is a star that serves that purpose with almost zero margin of error."
On Earth, the North Star is actually offset from the celestial north pole by a little less than one degree, meaning it appears to move in a tiny circle. Over time, that tiny deviation could lead to errors.
"I see. In that case, we can confirm our position at night using that star."
"Actually, you can see it during the day as well."
"Eh?"
Reiko’s words came as a shock to Jin.
As her creator, Jin knew better than anyone that Reiko's eyes were far superior to a human's. However, he hadn't realized she could see stars even in broad daylight. With vision equivalent to a 6.0 or 7.0 rating, the stars remained visible to her. Jin’s vision was around 1.5, so such a feat was impossible for him.
However, considering this world had much clearer air than Earth, it made sense that Reiko's visual acuity would allow it.
"If that's the case, then if I make a dedicated measuring instrument, we can calculate our position based on the time and the positions of the sun, the moon, and the North Star..."
For the time, they would use Hourai Island Mean Time (HMT), treating the laboratory on Hourai Island as 0 degrees longitude. From there, it was just a matter of measuring angles and performing the calculations.
"...That solves the navigation for the Hourai Island Fleet."
He passed the idea to Laojun, letting him iron out the finer points.
"Understood. I shall produce a prototype," Laojun replied.
"Now then, back to the problem at hand."
The fleet would be fine, but Jin shifted his focus back to the current project.
"A compass is essential. To make it work, we should avoid using iron parts in the ship as much as possible."
On Earth, modern ships are mostly made of steel, which causes magnetic compasses to deviate. Because of that, nautical compasses often use a gyrocompass instead of a magnet. However, jumping straight to a gyro was a high hurdle for this project, so Jin decided they would stick to magnetic compasses. That meant minimizing the use of iron components in the hull's construction.
Just as he reached that conclusion, Reinhard and Elsa arrived.
"Jin, what's wrong? It's already noon."
"Jin-nii, were you lost in thought again?"
It had become lunchtime before he knew it. Jin headed to the lounge with them, where lunch had already been served. The rest of the group had already started eating. Jin felt the stirrings of hunger himself and took his seat.
The menu for the day consisted of bread, stir-fried freshwater shrimp and vegetables, simmered itopo, and fruit juice.
"...Jin, how is the progress? Though I suppose asking you that is almost an insult," Reinhard said as they finished their meal and moved on to second helpings of juice. The other engineers all leaned in to listen.
"Ah, yeah. I have a general idea of how to handle it. Now I just have to build it."
"As expected! You truly are incredible."
The others nodded silently at Reinhard's praise. After yesterday’s demonstrations, everyone was fully convinced of Jin's skill.
"We’ve narrowed things down quite a bit on our end, too," Reinhard continued. "We plan to start discussing the interior this afternoon. Depending on the layout, we might need to make minor changes to the hull."
"That makes sense....By the way, who's handling the processing for the models?" Jin asked. Since he was tucked away in a side room, someone else had to take over his usual role.
"Who do you think?" Reinhard smiled mischievously, his eyes flickering toward Elsa.
"...Elsa?"
Elsa gave a small, shy nod, her cheeks flushing pink.
"Exactly. She is your top disciple, after all. Her processing speed and accuracy are actually superior to mine. Everyone was quite impressed."
"Is that so..."
When Jin looked at her, Elsa's face turned an even deeper shade of crimson.
As the break ended, Jin spoke with Reinhard and Elsa, explaining that they should avoid iron components as much as possible to ensure the magnetic compasses worked correctly.
"I see, that makes sense. I'll keep that in mind," Reinhard promised.
Reinhard and Elsa headed back to the afternoon review meeting, and Jin returned to his workshop.
"Now then, let's finish up this thruster."
For Jin, the solution was remarkably simple. If wind-attribute magic acted on air molecules and water-attribute magic acted on water clusters, what did earth-attribute magic act on?
The answer was "particles." From the molecular level up to massive boulders, earth-attribute magic acted on "mass" or "matter."
In other words, by utilizing the principles of Stone Bullet magic, he could generate propulsion regardless of whether the medium was air, water, or even dust.
"Though it does have one flaw," Jin muttered to himself as he modified the prototype. "The fuel efficiency is terrible..."
Because the magic acted on "mass," using it on air molecules resulted in significant energy loss. It was like using a heavy-duty dump truck to transport a single tennis ball.
"But you can improve it, can't you, Father?" Reiko interjected. Her voice was filled with absolute confidence in him.
"Of course I can," Jin said with a grin. "I just have to add three more magi-formulas."
He added a decision system to judge the size of the target, a classification system to categorize them into three stages, and a control system to vary the force applied based on that size. Effectively, he was applying the optimal amount of force for solids, liquids, and gases respectively. With these additions, the efficiency increased to a level comparable to the original Wind Thruster.
"You truly are my Father!"
As Reiko praised him, Jin finished rewriting the magi-formulas and reassembled the device. It was no longer a simple Wind Thruster.
"...Let's see. I'll call it a Jet Thruster."
Thus, the Jet Thruster, a specialized propulsion device for ships, was born.
With the remaining time, Jin let his mind wander through various methods for position tracking.
"I’ve got it! I could bury the markers so deep that no one could ever dig them up!"
It was a complete reversal of his previous thought—if the sky was no good, he would go deep into the earth.
"If the magic pattern is unique but the signal is weak enough that it's barely detectable, no one will go out of their way to try and unearth it."
In this way, Jin continued to put new ideas into practical use in the moments between his official duties.