When the banquet was completely over, it was already dark, and Hong Tao made another request, wondering how the captain or navigator of Luo Youde's boat navigated at night, because the boat was still moving and had no intention of anchoring. In addition, he wants to pick up Bo Xiaoer, who has been following the big boat, and now he has basically let go of this Luo Youde, and he no longer needs Bo Xiaoer to follow the big boat. I'm afraid he hasn't eaten dinner yet, and his safety is basically guaranteed, so don't let him suffer.

After Bo Xiaoer got on the boat, he was taken to the cabin below the deck by that Ah Cai to eat, judging from his attitude, he still didn't think very highly of the Tan family, and Luo Youde was not pretending to be polite. Regarding this issue, Hong Tao does not plan to delve into it for the time being, nor does he plan to fight for Bo Xiaoer. The problem of social status can not be changed overnight, let alone a foreigner, even if the Song Dynasty officials came, there was nothing they could do about this matter, rather than making both sides unhappy, it was better to use this opportunity to strengthen their own abilities, and when their abilities were big enough, it was not a question of what others wanted. At that time, whether you are used to it or not, whether you are happy or not, you must do things according to my rules, and you will not be unhappy, this is called strength!

As for the navigation skills of the captain or the captain of the ship, Hong Tao only watched it for less than ten minutes, and he was not interested. He doesn't know how to navigate at all, he's just relying on the experience passed down from his ancestors to operate the boat. The route marked on the chart and the details not marked on the chart are the key to his navigation, and he will have to be blind if he leaves the chart or changes to a new route.

Why, because he is completely relying on the data left by his predecessors. For example, if the route on the chart was to go straight south, he would rely on the information in his hands and in his mind to calculate the approximate time before turning with an hourglass and a simple instrument for measuring the speed of the ship, and then how long it would take to turn on the next leg of the voyage. Once there is a mistake in the calculation of time and the speed of the ship, it is over, and he will not be able to do anything except know that he can use the constellations to easily distinguish between the east and the west. Therefore, the current ocean routes are said to be ocean routes, but in fact, they are just a short-haul route spliced together, and there must be many stops along the way. Even if you don't need to stop, you have to go around and turn around just to be able to calibrate the error. Once these stops or markers are missing, the long-distance voyage will become a nightmare, as long as there is a little error, if it is not corrected in time, it will get bigger and bigger, and eventually the ship will be lost, and the real transoceanic voyage is not yet possible.

Hong Tao has seen the chart, it is very simple, the scale is not right, and the approximate location is about the same. Hong Tao didn't ask about the detailed parameters of this route, and it was useless to ask, people would not necessarily say that this was a very important trade secret.

The simpler tool for measuring the speed of a ship is a wooden plank that is thrown into the sea at the bow of the ship by a human being, and then the person walks to the stern at a fixed speed. When the wood chips and the person reach the stern at the same time, it is a fixed speed of the boat, and the specific amount is related to the speed of the person's walking, and each person is different. However, this method can only measure the relative speed of the ship and the water, not the absolute speed of the ship relative to the earth, and ignores the influence of ocean currents.

In fact, this method was still used in Europe hundreds of years later, and they tied a wooden barrel with a rope and tied knots of the same distance to the rope. When the ship is moving, the barrel is dropped from the stern and the knots are counted, and the speed of the knots is counted as many knots in a unit of time. In later times, the unit of speed referred to in navigation, the knot, was derived from this.

However, Luo Youde also provided Hong Tao with useful information, he said that there are several very powerful ship bosses in Guangzhou and Quanzhou, and they can use the astrological technique to use the position of the sun and stars to locate the position of the ship, which is very accurate, but he has never actually seen it. As for what this astrological technique is, he doesn't know anymore, those ship bosses are all treasures of sea merchants, and they will not easily come into contact with outsiders.

What is Astrology? Is it so mysterious and useful? Hong Tao's answer is yes, but it is an exaggeration. Astrology is very simple to say, when he was obsessed with sailing, he looked it up on the Internet and in the library, and made several sets of experimental equipment. In the end, it was concluded that it was useful to determine the approximate latitude of the ship, but it was not possible to measure the longitude of the ship, which could not be said to be useless for ocean voyages, but it was far from enough.

So what is this astrology? It is a set of wooden planks of various sizes, with a hole drilled in the middle and a rope threaded through it. Use different planks in different seasons to face one or more fixed star positions, make the bottom edge of the plank parallel to the sea level, choose a plank with the upper edge parallel to the target star, and then you can know the latitude of your ship on the chart. Although there was no concept of latitude at this time, depending on the number of planks, six to twelve horizontal lines would be marked by the person who knew the technique, which was roughly equivalent to the weft.

When it is really used, it is necessary to prepare not only a set of wooden boards, but also several sets of star-pulling boards for observing different target stars, and observe each other back and forth. Hong Tao used modern instruments to observe, and then made a star-pulling board to reverse this thing. It turns out that it is indeed possible to determine the latitude of the ship, but there is a problem, that is, if you want to sail around the world, not only do you need to know which stars in the northern hemisphere have a relatively fixed trajectory, but also know which stars in the southern hemisphere can be used as a reference, because the starry sky seen in the northern and southern hemispheres is different, for example, the North Star, you can't see it in the southern hemisphere. So in this day and age, basically no one can sail across the globe, who can know the starry sky of both the northern hemisphere and the southern hemisphere? Except for Hong Tao!

Even if Hong Tao knows the star map of the north and south starry sky, he will not use this primitive way to determine the position, this thing is too wrong, the difference of 100 kilometers on the sea is life and death, who will give their lives to similar guessing technology? Moreover, the astrology can only measure latitude and not longitude, which can be regarded as a lame leg. Just knowing the relative position of the ship from north to south is still not able to sail across the ocean, but also to know the relative longitude of the ship in the ocean from east to west, in order to accurately know the position of the ship.