Yeah, not a raft! The ebony logs are heavier than water.
Floating a boat is about displacement of water. Place a glass bowl in a tub of water and it will float, sinking into the water only to the point where the weight of the glass is equal to the weight of water displaced (by the air in the bowl, mostly).
But fill the bowl with water and it will sink to the bottom.
So you could make a boat from ebony, even though the ebony itself is heavier than water.
That's probably more physics than most people come here for, though...