There are a bunch of rafts around Zelda: Breath of the Wild, but they don't seem to be interactable and none of the NPCs so far have mentioned them. Have I missed some clue or interaction which makes them usable, or just do I need to use something weird like time freeze to move them around?
Turns out you have to use some non-Newtonian physics to move rafts: while standing on the raft, wave a Korok leaf at the sail or push an object held with magnesis against the mast. I could not get the magnesis technique to work with a sword, so either it's been patched out or only certain (heavier?) objects work.
Just get yourself a Korok Leaf and use it to make gusts of wind that will push the raft. From what I know it dose not do damage to the Korok Leaf. If you don't have one then you will have to use a normal melee weapon to hit it that will need be good and it hurt the weapon.
It sounds like that you want to go across the ocean. I would just use Cryonics to make ice pillars and glide from one of them to the next one.