On August 8, a hot and sunny day, Jin and his colleagues came to Lihot Village.

They were there to test their prototype air jet on a ship.

"I'm looking forward to it!

"It's going to be a lot of fun!"

Paelova Sondovik and Jed Alamold are with us.

There was a big commotion in the village of Rihot, as all the bigwigs had arrived.

"Well, well, well, Mr. Superintendent, welcome to our village!

While Paelova and Jed were being greeted with greetings like these, Jin, Eira, and Katya moved to the landing area.

They look around at the boats of various sizes tied up there.

"Hmmm, not so many good boats. ......"

"Why don't you stop worrying about the quality of the boats, Jin?　Why don't you just pick out the newest one you can and be done with it?"

"Yes, Jin-san. This time it is just a prototype. ......"

Jin thought back to what they had said, and decided that was a good idea.

"Okay. Let's try ...... that one then."

Jin pointed to what seemed to be the newest boat.

"Yeah, it looks good, doesn't it?"

The size of the boat looks good and I'm sure Paelova will give us permission as soon as we ask her for it.

"What do you think, Jin, Eira, Katya?

Speak of the devil, Paelove has arrived. Jed and the village chief are with her.

"Oh, yes. I think that boat is the right one.

"Hmm, that one. ...... chief, what do you think?　I told you how to use it on the way here.

I have no objection.

I have no objection. ...... Jin-dono, you may use it.

Thank you very much.

Thank you.

"...... this is another great ...... ......."

"...... as you say."

"......"

Paelova, Jed, and the village chief watched in amazement as Jin got more serious and modified the ship.

Eira and Katya seem to have gotten used to it over the past few days, at least they don't show it in their expressions.

"There we go."

Jin's modified vessel is a shallow-bottomed, wide boat about 4 meters long and 1.5 meters wide.

Two prototype air jets were installed on both sides of the boat.

In other words, they intend to use them not as <> but as <> to move the ship.

This is because we are using a magic circle instead of a magic crystal, which makes the control rough, so we decided to use an engine that injects air instead of water.

Also, we could not incorporate a warding function to prevent the inhalation of solids.

In this respect, most of the solids in the air would be dust and sand, and even if a bird or some other object were to get stuck in the engine, it could be quickly repaired.

Lastly, a magical board (plate) with a magic circle engraved on it, which has the effect of <>, is attached to the bottom of the boat. This would reduce the water resistance.

"Mr. Paelova, we are now going to test run the ship, would you like to get on board?

Jin called out from the boat.

The ship accommodates five people. Since Jin, Eira, and Katya are on board, there are only two more people to accommodate.

"Well, I'd love to, but I don't think Jed will let me.

"I'm sorry, Master Jin. We'll watch from the shore.

"Yes, sir."

Jin sits in the center of the boat. Eira sits near the bow and Katya at the stern.

"<>!"

Jin activates the air jet. The ship starts to move slowly.

"Oh, it's moving, it's moving!

Eira exclaims.

"Katya, I need you to steer the ship as I showed you.

"Yes, sir."

Katya, sitting in the stern, turns the rudder slightly and steers the boat away from the shore.

"Okay, we are going to increase the speed.

The air jet we have built this time cannot be controlled precisely, so the air volume is adjusted with a lever instead of <>.

Jin hoped to eventually use a wire cable or a rod to control the air jet like an accelerator.

Still, the power output was considerable, and the boat could run at about 10 km/h against the current of the river.

It seemed that the boat would be able to reach the village of Lileaz, which is located in the middle reaches of the Nosina River.

"I wish I could make it more powerful: ......"

The output is proportional to the input.

In this case, the input is free magic element (ether).

The efficiency of the magic circle is 1/50th to 1/10th of that of the magic crystal (magicrystal). The efficiency is 1/50th to 1/10th of that using magic crystals (magi crystals).

"Even if I wanted to improve the quality of the plate, I don't have the materials, so I guess I can't go any further.

"No, no, no, Jin, this is quite something!　Look at the shore. Paelova is looking at me like she wants a ride.

Eira is not a talker. She calls out to everyone if she knows they can't hear her.

Jin looked at the shore with a wry smile.

"Yeah, really. ...... but he should improve a bit too."

"Well, since Jin says so, you already have a good idea, don't you?"

"Of course. I'd like to increase the diameter and the speed of the airflow.

This method, of course, cannot go faster than the speed of the wind.

Therefore, Jin decided to increase the speed of the jet in order to increase the speed of the ship.

Let's give it a try. ......<>"

Jin widened the bore diameter by a factor of 1.2.

This is the limit, since there is a combination of the thickness of the material and its strength. But...

"Oh?

The speed had increased to the point where he could actually feel it.

"1.2 times the diameter means 1.44 times the area. That means that the amount of air that is sucked in has increased 1.44 times, which means that the jet speed has increased 1.44 times as well.

Katya did the calculations instantly.

"Yes. Well, it won't necessarily be exactly as calculated, but I'm sure it's about 1.4 times faster."

At the very least, the wind shear is noticeably different.

"I'd like to be able to go back to the middle basin."

As soon as Jin said this, Katya immediately started to calculate.

"If the river is flowing at 3 kilometers per hour here, the current speed is about 14 kilometers per hour. The current in the middle part of the river is about 15 kilometers per hour, so the boat should be able to reach a speed of at least 20 kilometers per hour.

"Oh, really?"

"Then we would need to increase the bore ratio by a factor of 1.2.

Dividing by 20 (16), we find that we need an aperture ratio of 1.25 times the area ratio. The square root of the diameter is about 1.118. Considering the loss of efficiency, he said 1.2 times.

"Cachéa is amazing. How could you do the calculations so fast?

Eira, sitting near the bow, was impressed.

"Okay, let's go back."

"Yes, sir."

Katya turns the rudder as far as it will go. The flat, shallow-bottomed boat is stable.

The boat makes a 180-degree turn and is now running with the current of the river at a speed of 17 kilometers per hour.

The prototype of the air jet is good. Now we just need to control it.

"We need to figure out how to make it more maneuverable!

"That's right."

Jin agreed with Eira's opinion.

Jin had never piloted a real motorboat before, so he decided to let it be as long as it was easy to use, even though it might be a unique way of piloting the boat.