I feel like the difficulty curve escalates very quickly. I had a run where I had a shark swarm, a megaladon, and three of the giant piranhas all swarming my ship at once. I was holding down my harpoon with the sharp upgrade the whole time but too many had latched on even will the stable hull and slippery hull upgrades. It's an addictive game, I'd just like it if maybe stuff like that didn't happen after just 3 checkpoints.
Edit: Try to get the sextant as early as possible. Ignore captain upgrades since the hull and tool upgrades are the only thing that really matter. Maybe the two helpers so you can focus more on the sextant upgrades