Chapter 41

When the banquet was completely over, it was already dark. Hong Tao then made another request, wanting to know how the captain or pilot of Luo Youde's ship navigated at night, as the ship was still sailing and showed no signs of anchoring. Additionally, he wanted to bring Bo Xiaoer, who had been following the large ship, aboard. Now that he had basically put his trust in Luo Youde, he no longer needed Bo Xiaoer to follow the ship in the dark. He was probably still hungry, and since his own safety was now more or less guaranteed, he didn't want Bo Xiaoer to suffer anymore.

After Bo Xiaoer boarded the ship, he was taken by Ah Cai to a cabin below the deck for a meal. From Ah Cai's attitude, it was clear that he still looked down on the Tanka people, and Luo Youde didn't pretend to be polite. For now, Hong Tao didn't plan to delve into this issue or fight for Bo Xiaoer. Social status issues couldn't be changed overnight, let alone by an outsider like himself. Even if a high-ranking official from the Song Dynasty came, they would be powerless to change this. Instead of causing discomfort for both sides, it was better to use this opportunity to strengthen his own abilities. When his capabilities were strong enough, it wouldn't be a matter of what others wanted. At that time, whether you liked it or not, you would have to follow his rules, and there would be no room for disagreement. That's what power is!

Regarding the navigation skills of the captain or the ship's leader, Hong Tao lost interest after watching for less than ten minutes. He didn't know how to navigate at all; he was just operating the ship based on the experience passed down from his ancestors. The key to his navigation was the route marked on the sea chart and the detailed information not marked on the chart. Without that sea chart or if he had to take a new route, he would be lost.

Why was this the case? Because he relied entirely on the data left by his predecessors. For example, if the route on the sea chart was to sail straight south, he would use the data in his hand and memory, along with a sandglass and a simple device to measure the ship's speed, to calculate when to turn after a certain amount of time, and then calculate when to turn again after the next segment of the journey. If the time calculation or the ship's speed calculation was wrong, it would be disastrous. Apart from using the constellations to roughly determine the directions, he couldn't do anything else. Therefore, what was called a long-distance route was actually a series of short routes pieced together, with multiple stops along the way. Even if no stops were needed, they still had to make a round trip to calibrate the errors. Without these stops or reference points, long-distance navigation would become a nightmare. Any small error, if not corrected in time, would grow larger and larger, eventually leading to the ship being lost. True transoceanic long-distance navigation was currently impossible.

Hong Tao had seen the sea chart, which was very rudimentary and had an incorrect scale, but the general positions were roughly accurate. He didn't ask for the detailed parameters of this route, as it wouldn't have been useful anyway. The other party might not have told him, as it was considered a significant commercial secret.

The tool for measuring the ship's speed was even simpler: a piece of wood thrown into the sea by a specialist at the bow of the ship, who then walked to the stern at a fixed speed. When the piece of wood and the person reached the stern at the same time, it indicated a fixed ship speed. The specific speed depended on how fast the person walked, and each measurer was different. However, this method could only measure the relative speed of the ship to the water, not the absolute speed of the ship relative to the Earth, and it ignored the influence of ocean currents, making it very inaccurate, though better than nothing.

In fact, this method was still used in Europe a few hundred years later. They used a rope tied to a wooden bucket, with knots tied at equal intervals. When the ship was sailing, they would throw the bucket from the stern and count the number of knots that went out in a unit of time, which gave the speed in knots. The unit of speed used in navigation, "knots," originated from this method.

However, Luo Youde also provided Hong Tao with a useful piece of information. He said that in Guangzhou and Quanzhou, there were a few very skilled ship captains who could use the celestial navigation technique to determine the ship's position using the positions of the sun and stars, which was said to be very accurate, though he hadn't seen it in action. As for what this celestial navigation technique was, he didn't know. Those few ship captains were treasures of the large merchants and rarely interacted with outsiders.

What was this celestial navigation technique? Was it so mysterious and effective? Hong Tao's answer was yes, but it was exaggerated. The celestial navigation technique was quite simple. When he was obsessed with navigation, he had researched this method online and in libraries and even made several experimental tools. The conclusion he reached was that it could determine the ship's approximate latitude, but it couldn't measure longitude. For long-distance navigation, it wasn't useless, but it was far from sufficient.

So, what was this celestial navigation technique? It was a set of wooden boards of different sizes, with a hole drilled in the middle and a rope threaded through. In different seasons, different boards were used to align with one or several fixed stars, with the bottom edge of the board parallel to the horizon. A board with the top edge parallel to the target star would indicate the ship's latitude on the sea chart. Although the concept of latitude didn't exist at the time, those who knew this technique would mark six to twelve horizontal lines on the chart, roughly equivalent to latitude lines.

In actual use, it wasn't just one set of boards; several sets of boards for observing different target stars were needed to cross-check the results. Hong Tao had used modern instruments to observe and then reverse-engineered the celestial navigation boards. It was proven that this method could indeed determine the ship's latitude, but there was a problem: if you wanted to navigate globally, you needed to know not only the fixed stars in the northern sky but also the reference stars in the southern sky, as the sky seen from the northern and southern hemispheres was different. For example, the North Star couldn't be seen in the southern hemisphere. Therefore, in this era, no one could navigate across the globe, as who could know both the northern and southern skies? Except for Hong Tao!

Even if Hong Tao knew the star maps of both hemispheres, he wouldn't use this primitive method to determine the position, as the error was too large. A difference of 100 kilometers at sea could mean life or death, and who would entrust their life to a method that was more like guesswork? Moreover, the celestial navigation technique could only determine latitude, not longitude, making it like a ship with one leg. Knowing only the north-south position of the ship was not enough for transoceanic navigation; you also needed to know the east-west longitude to accurately determine the ship's position.