My only complaints are for realism, the concept and feel of the game are great, keep up the good work!
As a 'MacGyver' type IRL myself, I would, in this situation, take a few precautions with the sharks, specifically I'd have a panel or something, full of sharp spikes, so when it bites the side of the raft it gets a mouthful of sharp rusty tin cans or somesuch.
Also, I applaud you on a plausible water desalination system, although based on the design, not super efficient. IRL I'd build it much more enclosed.
Also, something to think about for the future, it does rain from time to time in the middle of the ocean, a rainwater collector would be a good idea if you ever add weather cycles.
If you want models for any of these I can do them, but I only work in Sketchup.