How can I farm for Pirate Maps without a minion?

Here is a quick way to farm the ocean for drops. It takes advantage of artificial biomes by causing jungle monsters to spawn in the ocean, most notably Arapaima.

What you will need:

1. 50 jungle biome blocks. Mud with jungle grass will work as in the picture, lizhard temple blocks increase spawn rates however.

2. Yo-yo or tile piercing weapons. The yoyo can be thrown out the hole in the side of the structure and guided down into the ocean water. (I was using the Eye of Cthulhu yo-yo, A drop from Mothron)

3. Water candle, battle potions, anything to increase spawn rates.

4. Banners are optional but will help you to kill enemies that much faster.

The block of ice above the structure was used to farm hallow and ice biome keys. It obviously isn't needed to farm pirate maps so disregard it.

As for building it, the design doesn't have to match this one exactly but you will need a couple key features.

1. The structure needs to dip into the water and needs sloped sides. This will cause Arapaima to glide underneath the structure. Keeping the blocky sides will cause them to get stuck instead of sliding against the slopes.

2. You need to stand in water to attract water enemies to your position. All it takes is a little box that holds 2 buckets worth of water.

3. Platforms to catch the loot. You can either build the platforms or it will drop to the ocean floor for you to collect. Just a matter of convenience.

Obviously if you do not have a decent minion to help you, you'd have to do it yourself. AFAIK monsters from statues does not drop biomes loots such as the pirate map you need so that is not an option.

Increase Spawn

This is almost a given for hunting monster drops. The ocean itself is a good place to tap on since every tile of water can spawn ocean monsters and each have a chance to drop since it is already within the biome. To boost it further you can build a layer with solid blocks above the ocean with another biome, to that I recommend corruption.

The corruption spawns a few variant of flying monsters on the surface level. With spawn rate boost such as Water Candle and Battle Potion you'll find yourself be constantly swarmed with monsters. The map have a fixed drop for every kill within the ocean biome so there is no need to prioritise any monsters, just kill all of them.

Swimming

Since you are to fight within the ocean biome, most of it is within the large body of water. Being able to freely move in the water will open a much larger area in which you can farm from, also allowing you to loot items dropped in the deeper parts of the ocean.

Minimally I will suggest Diving Gear but if you want to take it further and farm a Neptune's Shell it'll be even better. Having either will allow you to swim near the surface of the water between the extra biome you made and ocean, maximising the amount of area in which monsters can spawn.

Combat

If you are having trouble coping with two biomes of endless onslaught but still wish to maximise the farming efficiency, you can consider doing a few things:

1. Open gaps between the extra biome, allow you to jump into the water or out of it freely. This is a double bonus allowing you to escape to the side with less monsters to heal or to the side with more monsters to farm.
2. Build a room and use weapons that can hit through/pass walls, a couple of suggested weapons include Crystal Vile Shard, Daedalus Stormbow(you'll need to build the area properly to use this effectively) and a gun with Chlorophyte Bullet
3. Build a room near the edge of the ocean and move the nurse there for quick healing during combat.
4. Get a pair of wings
5. Fill the deeper end of the ocean nearer to the surface with sand so you do not need to dive as much to get the loots