DREDGE

• Here are my recommendations for each research tab:
  • Engines: You get two distinct paths. I recommend the top path first that ends immediately with the 1x1 size Jet Drive Engine and buying a bunch of those. They are almost as fast as the final tiers of the bottom path and save you a lot of research parts. As well, because of their shapes, the large engines on the bottom path are awkward to fit into your ship, and even at the end you won't be able to use every engine slot efficiently with them. Finally, they work as damage insurance. If your hull gets damaged it X's out a random tile of your inventory, and anything within that tile gets broken until you repair it. If you have one of the big engines then taking 1 damage can completely wipe out your speed. If you have a bunch of little engines it isn't such a big deal to lose one of them. Ultimately you'll need both the big engine and the jet engines for the fastest possible speed on the end-game boat, but it was one of the last research branches I did since the jet drive was so effective.
  • Rods: You will need to be able to fish up every type to get through the game. There are many mandatory quests that ask for a specific fish and you must have the appropriate rod to be able to get it. Most of them are only* acquired through research. The combination ones are more for convenience since it only takes a bit of time to go back to the shipyard and switch rods, but that does get annoying. There are a lot of options, but you can't really go wrong here as long as you don't completely neglect this page. I went for the combination coastal/shallow/mangrove/volcanic and abyssal/hadal/oceanic rods and was pretty satisfied.
  • Nets and crab pots: These are mainly for passive fishing which saves a lot of time from having to manually fish for money, at the expense of having to repair them from time to time. You get some free starter ones which are sufficient for the quests that need them, but the upgraded ones are much more profitable. These are not as crucial to research for the main quest as engines or rods, but they really help with affording upgrades. It's up to you which you prefer, nets are more convenient but you have to sacrifice some rod space, while with crab pots you have to spend more time fiddling with them. Personally I recommend the middle line of the nets since they have by far the highest passive yield.

• There are only two sellable dredge treasure that are needed for a sidequest: The one requested by the distraught father in Little Marrow, and the dog tags. Every other treasure that you can sell to the trader has no purpose other than selling, even if the flavor text suggests otherwise.

• You should look around every island carefully. There is a lot of hidden optional stuff in this game and most of it you would only find by simply stumbling upon it while exploring. These will often give unique rewards you can't get anywhere else, including permanent passive upgrades, or really good unique equipment that bypasses the need for research. A lot of these don't need a dock or anything, just approach stuff that looks interesting and see if you get an interaction prompt.

• There is no time limit.

• The game does not explain many of its mechanics. For example, the foghorn and light switch have hidden functionality that is never hinted at and is not obvious. So you should experiment with your tools in different situations.

• All the stats you get from installing equipment stacks, even if doesn't seem like it would make sense. For example even if you have some big ultimate rod, you can throw on the basic 1x2 starting rod in a free spot to improve your fishing speed. So consider storing old gear instead of selling/destroying it unless you have something better of that size.

• There is a hidden second ending. But you can get both endings on the same save file since the game does not save after you beat it.

• When you use the telescope out at sea, make sure to turn your view with the right analog stick instead of the left. Using the left analog stick will physically turn your ship which takes up ingame time, like sailing around. Using the right analog stick is just like looking around and doesn't take ingame time.

• When deciding which islands/DLC to tackle first, my recommendation is to follow the general main story quest, but do the Iron Rig content for that location just after finishing its main story content.
  • Marrows, then the Marrows Iron Rig content
  • Gale Reach, then its Iron Rig content
  • Stellar Basin, and then its Iron Rig content (note that you can do Stellar Basin before Gale Reach if you'd like, it's a bit easier)
  • Pale Reach (if you have this DLC)
  • Twisted Strands, then its Iron Rig content
  • Devil's Spine, then its Iron Rig content