Marine replacement engines can be bought from online engine stores, such as Marine Engine Depot and Jasper Engines. Local motorsport stores that sell boats and engines may also carry or be able to get replacement engines.
Boats typically have one of two different types of propulsion systems. There are outboard motors, which are portable disconnected motors that hook on to the back of the boat, and there are inboard motors, which sit somewhere inside the boat and power propellers on the outside of the vehicle. Outboard motors are typically easy to replace if they break down, because they can simply be disconnected from the boat and a new one can be put in its place rather quickly. Inboard engines are more difficult to replace because they sit inside the vehicle and require a more complex wiring system.
Both inboard and outboard motors can be bought through various online motorsport retail companies. Online sites such as Marine Engine Depot and Jasper Engines specialize in inboard engines, and offer engines of all different speculations to work with as many marine vehicles as possible. Jasper Engines makes and sells remanufactured engines, which means old used parts are combined with newer parts to create a working and cheaper version of a specific engine.