I know moving while overloaded costs you stamina, but shouldn’t trying to swim through deep water be blocked if your overloaded? It seems ridiculous to go swimming for miles (figuratively) and pay nothing more than half your health even though you’re heavily overburdened with Iron Ore. Similar, I would think a raft/bull boat should sink or at least travel more slowly (faster decay rate) when you have too much with you.
The weights are unitless, so we can’t be sure they’re pounds. For example, a furnace has a weight of 24 in the game, and a bow drill is 5. I don’t think of any weight or mass unit that would have a blacksmiths furnace weigh less than 5 bow drills.