Dealing with tides

"And then the Tide Peoples accused surface inhabitants of eating sealife including themselves, while surface peasants accused Tide Peoples of flooding their lands to steal their fields and their food. Mnau, the god of the Sun was supporting Tide Peoples, while Ikkra, the god of the Moon supported peasants. The Two Sky gods never disagreed with each other until that moment and the war almost started. Luckily, the winter and summer spirits managed to negotiate with them and agreed that the sea can rise only while Ikkra is not in the sky."

— Inerto tale of the origin of tides

Tides are known in our planet as the periodic rise and fall of the sea level caused by solar and lunar gravity combined with Earth's rotation. Like pimples appearing on skin, some people apply lateral pressure with their fingers causing an outward force in order to break them by bulging. This can give an intuitive idea of how gravity acts here, if our hand had the size of a planet and we start compressing the oceans with our fingers, the displaced water will amount at other place, and there would be locations with higher sea level than others. As the planet is rotating, some observer on the surface will be travelling to high and low sea levels as the day passes.
In Noo the same theory is followed, what it changes are numbers. As in Earth the Sun and Moon cause the tides, in this case, in Noo it's their Sun and their own planet on the other side of the portal, (for more info Noo's Spiral Space who causes them, and while the mass of the Moon is 81 times less than the mass of the Earth, the mass of the other side of Noo is the same as the mass of the side of Noo where we are. Also, the distances between the two parts of Noo are shorter than the Moon-Earth distance, making the tidal forces way bigger. So as in Earth we talk about tidal ranges of centimeters or meters, in Noo we are talking about tidal ranges of tens or hundreds of meters high.

The tidal lowlands

By hundreds of meters high I mean sea water can enter into continental areas and flood entire countries every time it rises. If this happened daily as in Earth, mega-tsunami erosion would have been so powerful that continents couldn't exist, because all lifted land by tectonic movements would be sweeped by the sea quicker than it can rises. Luckily, rotation of Noo respect its other part is slower, taking 270 days to complete, so water rises not in hours but in months.
This creates regions named Tidal Lowlands, where by average almost half of the year are underwater, and the other half became mainland. These regions have developed amphibian characteristics, especially for lifeforms that don't move. Examples of this are the giantic water lilys, which grow up in the underwater season. The biggest species are the Inerto water lilys, which can grow 200 meters tall, and their disks reach by average radius of 30 meters long. Some other plants hibernate during underwater season creating shells, like the Crab Tree of Kurug. Most of these plants have to create resistant and waterproof wood, making them a valuable material. Fauna usually migrates with season, alterning birds, insects or other type of land animals with fish and other sealife creatures.

How to sail

The case of returning from your holidays with your family at the mountain to your work as a fisherman and realizing the sea is 50 km away of your boat, or the opposite case, realizing your boat is 50km away from the coast if it has remained moored or even floating, are the main reason of why build a port it's difficult. Small nomadic communities can carry small boats to fish when the sea level changes, but for bigger ships it's not that easy.
The first method is living in an amphydromic point. This places exist as equilibrium points between a zones with low sea level and high sea level. Most of them are in the middle of the ocean, but a few ones are located near the coasts. These places are rare to find but very useful to build your port. In fact every coast has its tidal range as a result of multiple factors, so you can find a piece of land where tides are relatively small if anyone has arrived yet.
If you are unlucky the second method consist of living in mountains near the coast. Some ports are built in high cliffs where the sea can only go up and down and not inside and outside. Mountain ports are the most common ones, and they are located at points where the coastline only changes a few meters inside, so boats can remain moored with reasonably long strings. The problem of this method is the weather, it's not recommended having your ship in a cliff when a storm strikes, so make sure you recollected enough resistent lowland wood.
The third method is simply having thousands of people working for you in order to built a channel to your home. These channels are located within the sea and capitals of powerful states, and they are pretty big, I'll probably draw one of them when I have time enough. The Cave Peoples are often hired to do this task and that's because their skills in digging, and the profits they have with the land they extract, because they also need to build underground dykes to control floods caused by tides.