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He is not asking for water physics, he is asking how to make an object that floats in water. There are items that float in the water in Skyrim.
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Well, if you read the title, his posts, and any replies you would see that physics is mentioned 12 times (before your post) and Havok is mentioned 4 times. It's called buoyancy, and to simulate a buoyant object you need some kind of "physics". So an "object that floats in water" would indeed need physical simulation on the object and to recognize it is in water. Hence, "water physics". Anyway, enough of dealing with your unnecessary and unhelpful reply / attempt to call me out.
What I learned is that indeed, some Havoked objects do float in water. I've never seen it as none of the objects I've ever dropped float. What that tells me is that Bethesda didn't spend a lot of time on making objects float that should, because if I drop certain objects that I expect to float, they sink like a rock. And certainly no boats in the game are Havoked... they are all completely static.
I found a http://niftools.sourceforge.net/forum/viewtopic.php?f=38&t=3274&start=0 and the person got somewhere with it. I went ahead and attempted myself by leaving the collision the boat already had intact, and adding my own collision that would stay below the boat and not interact with the player or any objects in the boat. The author of that topic had many problems, like the boat damaging the player, or adding a cabbage would sink the boat. The boat would also stop dead in its tracks if it ran into a fish. Anyway, after a lot of messing with the collision settings, I found that I had to up the mass, up the angular damping tremendously, and lower the max angular velocity and linear velocity. Otherwise it was severely unstable and would capsize or react violently to the fish or the player touching the bottom. My attempt so far still reacts to the water current but it moves slowly. In the thread I linked he had to choose between damaging the player or the boat sinking, or not reacting to the current. Since I added my own collision to the root node in NifSkope this isn't an issue.
I may upload a video sometime of my test. Just from my testing though it doesn't seem like it'll ever be stable enough for a mod... When I save the game in the boat and then reload, it'll be in the wrong place. Or if I reload and try to move the boat again the collision will go funky. It seems like I can only place a boat at me once in a new save and then after that the collision goes wonky. It's possible using a different OL_LAYER, Motion System, or Quality Type may provide better results but I don't really know if I'm going to spend more time on it. I also have no idea what would happen with NPCs in the boat. The static boats can have sit activators placed, but I doubt that's possible on a moving boat. Unless of course you can somehow move the activators along with the boat...
Edit: I don't know much about scripting so it's kind of wonky, but I attached a script to the boat that blocks the normal activation (so it doesn't go into my inventory) and instead applies a Havok impulse to the boat. So if I spam the activate key I can make the boat go forward more than what the water current provides. Unfortunately still when you load the savegame and such and you were in the boat, it'll be "sunken" and then rise up out of the water until it decides that it's buoyant, so what I effectively made is a "hoverboat". If I used the ship static I guess I would have an airship, hah.

Of course there are probably better ways of providing Havok impulses to the boat rather than hitting "E" constantly. But I don't know enough about scripting.