i just made a mesh boat with physical when i run it its ok but when i stand up it become convexhull

[Rolig Loon]

That is a little peculiar, but you had at least one link in the linkset that was already convex hull -- the part that you created as mesh and uploaded.  When you sit or stand up, you are changing the linkset.  That action may be enough to trigger the servers to make the rest of the object convex hull too.  In the end, though, it should be an advantage for you because the L.I. of the boat probably decreased, unless you have linked cut prims to it.  Why are you concerned?

[Rolig Loon]

That is a little peculiar, but you had at least one link in the linkset that was already convex hull -- the part that you created as mesh and uploaded.  When you sit or stand up, you are changing the linkset.  That action may be enough to trigger the servers to make the rest of the object convex hull too.  In the end, though, it should be an advantage for you because the L.I. of the boat probably decreased, unless you have linked cut prims to it.  Why are you concerned?