You've discovered two of box-modeling's most powerful tools: extrusion and moving vertices. Now, it's time to discover the third one: subdividing. Now, the hull will begin to look like a boat.
Press A to deselect all vertices.
Select Edge Select mode on the 3D View header.
Press B to do a Border select to select the edges of the sides of the boat, but not the bow or the stern, as seen in the following image:
Press W to get the Specials menu. Select Subdivide with theLMB.
On the left, in the Tool Shelf, a sub panel is labeled Subdivide. Make sure that the arrow next to the word Subdivide is pointing down. Change the Number of Cuts to
3. Blender will cut each of the edges into three as shown in the following image:
Change to Vertex Select mode in the 3D View header.
Deselect all the vertices. Select the vertices of the bow on the left.
Press Numpad 7 to change to the Top view. Use the Ctrl+MMB, Shift+MMB, and the mouse to zoom and...