The weight being more gradual is already implemented in the cart (which is VERY annoying) and the armor/weapons. That's why sometimes i just run naked around the island with my loot. XD So i think the current system is ok. I would just change the cart weight to be fixed tbh.

About the boat, the only thing that annoyed me is the helm control and no interface tip on how to control it at first. If it had its controls in the corner like when you start the game and had a key to "lock" the helm (like Q auto-walks) but made the helm spring back in "unlocked" mode it would be at least more intuitive.

Seeing the boats health is just a single key stroke to equip the hammer, so its no big deal just like the cart. The main problem is seeing whats in front of me because of the sail. X_X