Late Yuan Dynasty: I am the true emperor

Chapter 255 Preparations before Crossing the River (Part )

After deciding on the strategy, Lu Jin immediately pulled Yu Tongyuan, Liu Chuanyi, and several leading craftsmen together to discuss the renovation plan.

The masts on these six ships were of no use and were all removed. The three ships that attacked Dangtu were replaced with foldable ladders.

Lu Jin pulled the two young generals and whispered to them that the wall of Dangtu city was less than two meters high, but the moat outside was extremely wide, several dozen meters wide, and connected to the Yangtze River, so large ships could sail through it. These ships could then sail directly to the city, and you would be able to overlook the city when you stand on the ship. Then you could use a few rounds of artillery fire to drive away the defenders on the city, and then put up ladders and springboards directly on the city, and the soldiers could continuously pour onto the city wall from the ship, and then Dangtu could be broken.

The two children were stunned. They didn't expect there was such a way to attack the city. Liu Chuanyi even asked, "Has the commander already thought of this method to break the city?"

"Yes." Lu Jin nodded. "As early as when I captured Hezhou, I went to the top of Hezhou City to see the terrain on the other side, and I thought of it."

The two children were even more surprised when they heard this. They didn't expect Lu Jin to be so patient and not say it until now.

As if he could see through their hearts, Lu Jin asked, "Are you thinking that I was really able to hide it and didn't tell anyone until now?"

"." The two children were shocked as if they had seen a ghost when they heard this.

Lu Jin then explained, "Why did I hide it? Because this method can only win if it is used unexpectedly. If it is revealed in advance and discovered by the enemy's spies, it is actually very simple to defeat this method. Just tear down the southern city wall, move inward twenty steps and rebuild the city. This way, it will be difficult to jump directly onto the city wall from the boat."

Liu Chuanyi suddenly realized, "The Marshal is afraid that the news will be leaked and the enemy will move inside the city wall?!"

"That's right. I've only told you two about this, so you two have to keep it to yourself. No one is allowed to tell anyone until the day of the final siege, or I'll beat you to death."

"Don't worry, Marshal. We are not stupid and we will definitely not tell anyone." Liu Chuanyi assured him quickly. Just kidding. This was a great achievement given to him by Lu Jin. How could he possibly tell anyone?

"Yeah." Lu Jin nodded, then gave further instructions.

"This is the method for attacking a city, but it is not easy to accomplish. The difficult part is how to get the boat to the top of the city. First, you have to send a small boat to explore the way ahead to see if there are any hidden stakes laid by the enemy. Then you have to do a good job of fire prevention. During combat, all decks must be covered with a layer of wet sand, and water-soaked anti-arrow curtains must be hung on both sides of the ship. The main components such as the beams and pillars must be coated with a layer of wet mud to prevent the enemy from firing rockets from the top of the city or the two banks and setting the ship on fire.

"At the beginning of this year, when Xu Song attacked Jiangzhou, the Jiangzhou governor used this method to defeat Xu Song's Red Army. He first inserted plum blossom stakes in the river, and when Xu Song's warships were stuck and could not move, he ordered his soldiers to fire rockets to burn the ships. In that battle, countless Xu Song soldiers were burned or drowned, and the river water turned red, with corpses floating all over the river.

"Although we didn't fight this battle, you two should take it as a warning. In future water battles, be sure to pay attention to hidden stakes and fire prevention."

"Yes."

"I remember."

Both children nodded very seriously. Since someone had already used it this year and achieved such an outstanding result, it might be imitated by others. Now that Lu Jin has reminded them, of course they have to be careful. This is a way to save lives, how can they not remember it?

At this time, Yu Tongyuan asked again, "Marshal, what about me? Do I have anything to say about quarrying?"

"You? Row the boat to the vicinity of the quarry and fire at the shore. Oh, there is one thing you need to pay attention to. You must cooperate with the infantry commander and don't fire at our own soldiers."

"Just, that's it? That's all?" Yu Tongyuan said in astonishment.

"What else do you think?" Lu Jin stood up, patted his shoulder, and walked away.

Only Yu Tongyuan with a depressed look on his face and Liu Chuanyi who was laughing secretly were left.

Then the two men began to direct the craftsmen to transform the ship. The ironworks also sent cannons and began to install them on the ship.

Wang Dayuan stood on the shore and watched the craftsmen busy. When he saw Lu Jin had finished talking to the two young generals, he came up to Lu Jin and asked, "My lord, when are we going to build the sea ship?"

Lu Jin shook his head. "No hurry. It won't be too late after we take Jiangdong. Even if we build the ships now, we don't have an outlet to the sea. And I plan to build a regular shipyard, not the kind that builds a few ships and then stops. So this shipyard needs to dig dry docks and other construction facilities. These things can't be rushed."

But Wang Dayuan still reminded, "But my lord, I heard that if you want to build a sturdy and durable sea ship, you have to prepare the wood several years in advance and dry the wood in the shade before you can use it to build the ship. Even if you don't start construction now, you have to start storing the wood in advance."

Lu Jin still looked unhurried and said, "The timber is being stored. The logging work in Huoshan has never stopped, so we still have some timber reserves.

"As for the issue of drying in the shade for several years, I have a way to save time. It can be done by artificial drying technology. We can build a wood drying room and dry the wood in one month. The effect is equivalent to ten years of natural drying in the shade. This way, we can save a lot of time."

"Is this possible?" Wang Dayuan asked in shock.

Lu Jin nodded affirmatively, "Don't forget my last name is Gongshu."

Seeing that Lu Jin was confident, Wang Dayuan stopped urging him. However, he asked about the sea vessels again, "What is the difference between the sea vessels that the lord mentioned, which are three times faster than the Fuzhou ships, and the Fuzhou ships?"

Lu Jin did not answer directly, but asked, "Sir, you have been studying physics for two months. How is your mechanics?"

Wang Dayuan thought for a moment before answering, "I can only say that I am new to the subject. I do understand the concepts, such as buoyancy, carrying capacity, pressure, thrust, density, resistance, friction, etc., as well as the pulley formula. Through different combinations of fixed and movable pulleys, one person can lift a huge weight. It is truly amazing."

Lu Jin nodded. "Since you understand these basic concepts, it will be easier for me to explain them to you. Let's talk about how to increase the speed of the ship. Let me ask you, what are the conditions that affect the speed of the ship? Only when you know this can you come up with a solution."

"This..." Wang Dayuan was stunned by the question and couldn't think of it for a while.

Lu Jin didn't expect him to become an expert in mechanics after just two months of study, so he directly announced the answer, "It's actually very simple. There are only two points: the resistance the ship encounters when it moves forward, and the power required to drive the ship forward." Wang Dayuan pondered for a moment before nodding, "It seems to be like this."

Lu Jin continued, "First of all, let's talk about resistance. The bow of the Fuzhou ship is flat. It's like you are holding an open umbrella on a windy day, and then walking against the wind. Do you think you can still walk? I'm afraid it will be difficult to walk. This is the resistance imposed on you by the headwind. So what should you do if you want to reduce the resistance? Of course, put away the umbrella, and try to bend your body to reduce the area of ​​your body facing the wind.

"It's the same with boats. A flat bow creates a lot of resistance in the water, just like holding an umbrella against the wind. The boat won't go fast. So what shape should the bow be in to make it go faster? Just look at the fish in the water. The fish's body is spindle-shaped, with a pointed, round or flat head and tail. The bow of a boat with the fastest speed should be pointed and thin, like a sharp knife out of its sheath, cutting through the water and slicing through the waves!"

Lu Jin squatted down, picked up a branch, and drew a shape on the ground, which made Wang Dayuan's eyes light up.

"Draw a sword to cut the water, split the waves, what a good phrase, really vivid!"

Lu Jin added, "This type of bow is pointed and upturned, floating on the water. The bow and the reflection on the water surface form a shape similar to an open pair of scissors, so it can be called a clipper bow.

"The clipper bow has another advantage, which is its excellent wave-piercing performance. This section of the bow that extends forward can provide additional buoyancy for the bow, making it easier for the ship to quickly raise its head in big waves. This is the role of buoyancy. Do you understand?"

Wang Dayuan nodded. "I understand. The buoyancy of a ship is the reverse force exerted on the ship when the displaced water is backfilled. The forces act mutually."

"Okay, you can understand it that way." Lu Jin nodded.

"Now that we have discussed resistance, what about motivation?"

"No, resistance is not the only factor. In addition to the shape of the bow, there is also the aspect ratio, which is the fatness of the ship. The aspect ratio is the ratio of the length of the hull to the width of the freeboard. The aspect ratio of a Fuzhou ship is usually around 2 to 3, just like a large wooden basin. The advantage is that it can carry more cargo, but the disadvantage is that it has great resistance and a slow speed.

"Look at the bamboo poles floating in the river. They are long and thin, so they drift very fast. This thin and narrow shape allows them to swim faster in the water. The same is true for boats. To increase the speed, the boats must be made as thin and long as possible, like an arrow shot out. The Fuzhou boats are short and flat, like a shield facing the wind, so they cannot run fast."

Wang Dayuan nodded when he heard this. "That seems to be the case. Then what is the appropriate length-to-width ratio? We can't really build a boat shaped like a bamboo pole or an arrow, right?"

"Of course not. From my experience, if you want to reach a speed of more than ten knots, the length-to-width ratio must be at least 4, and 6 to 8 is most suitable. If you pursue extreme speed, you can also reach about 12.

“The bigger the length-to-width ratio is, the better it is. The thinner and longer the boat is, the larger the length-to-width ratio is, and the more difficult it is to turn around, and the larger the turning radius is. In terms of turning flexibility, this is exactly the opposite of a wooden basin.

"Think about it, is it easier to turn a wooden basin in water or a bamboo pole?
"So we need to strike a balance. As the saying goes, too much is as bad as too little. Too big is not good, too small is not good either. If the hull is too thin and long, the material and structural strength requirements for the keel will be higher. If we ignore the material strength and try to lengthen the hull, it will only lead to one consequence, that is, the total longitudinal strength will be too low. When the ship is sailing through big waves, the keel wood of the hull will not be able to support it, just like a chopstick, snapping in the middle and breaking into two pieces, causing it to sink."

Wang Dayuan imagined the scene and couldn't help shuddering. He asked again, "Then how big a ship should we build?"

Lu Jin thought for a moment before saying, "Let me do the math. If the freeboard is 6 meters wide and the length-to-width ratio is , then the length of the ship is meters, or about zhang, which is twice as long as the building ship in front of us."

Wang Dayuan had known for a few days that Lu Jin was used to calling meters "meters", so he could understand. Then he saw Lu Jin using the building ship in front of him as an analogy, and learned that the sea ship to be built in the future would be twice as long as this one, and he was immediately shocked.

"Isn't this long too long?"

"Not long. The length-to-width ratio is only 6. I'm being very conservative. If we're more aggressive, we can make it 8, which means the ship will be 80 meters long. But that's not necessary. And a ship this long would need a giant tree as the keel. Such towering trees are hard to find, and transporting them is also very troublesome. We should cherish the people's manpower and not cause trouble for them."

As Lu Jin was talking, he was writing and drawing on the ground with a branch. Wang Dayuan was watching from the side and saw that Lu Jin was doing a vertical equation. There was also a horizontal equation next to it. All of them were modified Arab numbers, including calculations of the length and width of the ship. After a while, Lu Jin clapped his hands, stood up and spoke.

"I've roughly calculated that it's 60 meters long, 10 meters wide, and 4 meters empty. Multiply that by the square coefficient of 0.75, and the empty displacement is about 1800 tons, which is the weight of the ship itself. The full draft is about 7 meters, and the full displacement is about 3150 tons. It can carry 1350 tons of people and cargo, which is about 270 million catties, or about dan."

Wang Dayuan was somewhat shocked when he heard this. He was not shocked by the loading capacity of the ship, but by Lu Jin's calculation itself.

"This ship has not even been built yet, but my lord has already calculated how much cargo it can carry?"

"Well, what's so strange about this? The loading capacity of a ship is something that should be considered during the design phase. It's impossible that the ship is built without knowing how much cargo it can carry, right?
"And this isn't a difficult problem. Based on the known length, width, draft, water density, and approximate square coefficient, we can calculate the load. It's such a simple problem, there aren't any unknown variables, and we don't even need to write an equation. In my family, even an eight-year-old should be able to do this. If you can't do this, you deserve a beating."

"." Wang Dayuan was stunned by what he heard. He finally understood what Gongshu meant by taking the Mathematical Classic as the basis.

For a question like this, let alone an eight-year-old child, even in the Yuan Dynasty today, I am afraid that many great scholars of the time would not understand it.
Lu Jin then said, "Since you mentioned building a sea-going ship, then don't be idle. Start drawing the blueprints and designing it now, and then ask me to review it. Once it's approved, ask a craftsman to make a scaled model to verify its feasibility."

"A scaled-down model?" Wang Dayuan asked doubtfully.

"Yes, you can make a small boat in proportion to the appearance of a real ship. A real ship is ten meters wide and sixty meters long, so you can first build a small boat that is one foot wide and six feet long. The construction process is the same as building a real ship. In this way, you can find problems in the process of making the model. If there are problems, you will know how to modify them when you build a large ship.

“Before doing a large-scale project, you must first verify the model. This is my Gongshu family’s secret method of saving money and grain costs. Otherwise, you may come up with a good idea, but before the thing is built, you don’t know whether it will work. If it fails, the materials and labor of a large ship cost a lot of money, and it will all be wasted. So you have to make a small one first to test the waters.

"If you are making a delicate gadget, such as a watch, with very delicate parts inside, you can first make a scaled-up model before making the real watch, and make the dial the size of a wooden basin. In this way, the tiny parts inside can be seen at a glance. Once the large model is made, you can shrink it down to make the real thing."

"So that's how it is. That's really great, but my lord, you only talked about how to reduce resistance, but you didn't mention the power of the ship." Wang Dayuan couldn't help but remind him.

Hearing this, Lu Jin said, "This is simple. Let's take holding an umbrella in windy weather as an example. This time, you are holding the umbrella with the wind. The larger your umbrella cap is, the greater the thrust of the wind you will receive. The greater the thrust of the wind, the faster you will be dragged by the umbrella.

"It's the same for ships. How do ships move? They rely on the wind. The larger the sail area, the more power it can provide to the ship. So the sail should be made higher and wider. The width of the sails of ordinary Fu ships is usually no wider than the freeboard width. For this new ship, you can make the sails wider, wider than the hull. In this way, the sails can absorb more wind power and sail faster."

(End of this chapter)