An inboard is a four-stroke automotive engine adapted for marine use. Inboard engines are mounted inside the hull's midsection or in front of the transom.
The engine turns a drive shaft that runs through the bottom of the hull and is attached to a propeller at the other end.
Many personal watercraft (PWCs) have two-stroke inboard engines that burn oil as a lubricant along with the fuel. New-technology two-stroke PWC engines are direct-injection engines and burn cleaner than conventional PWC engines.
Steering of most inboard boats, except PWCs and jet-drive boats, is controlled by a rudder behind the propeller.