The Inboard Power Boat, Has been around the longest. Basically an engine mounted inside the boat and driving through a shaft to a propellor outside the boat.

Apart from the obvious differences of engine size, inboards have 2 distinct types. The displacement and the hydroplane. These further have several engine size classes

Displacement Boats This term is a remembrance of boats of old, when they actually pushed their way through the water "displacing" is as they went, this is what causes the wash or wake behind a boat, as the water rushes in behind from where the boat has pushed it out of the way. At racing speeds modern displacement boats do not actually displace much water at all and become planing hulls, at very high speeds leaving a wake only a few centimeters high. We still call them displacement boats though.

Most modern displacement boats ore the rear engine design. This is just what it says the engine is mounted at the rear of the boat and drives through a shaft to a v drive gearbox forward in the boat. This allows a much flatter shaft angle so the propellor pushes the boat forward, and not into the air.

Mid mount engines, have the motor mounted in the center area of the boat. These generally drive the propellor shaft directly and have a much steeper angle on the shaft, which at high speeds will try to lift the boat from the water.

Front engine boats. These are now comparatively rare, they were however the state of the art before the development of rear engine boats. They were called racing skiffs. They were really center mount boats with the driver at the rear, to add weight to the back of the boat to try to keep the propellor in the water

Hydroplane Boats Modern hydroplane boats are what is known as a 3 pointer. This means the boat rides on 3 points, the propellor and the tips of the 2 sponsons. Sponsons are best described as almost 2 other small boats built into the hull and protruding below the rest of the hull. This is an over simplification though. At speed the boat rises onto the sponsons allowing air to rush under the boat lifting it from the water. The balance of these boats is very critical. If they ride too high in the front, they will not glide over the water, but try to take off. This is not a good thing. If the nose too low, they will try to push the nose into the water. This also is not a good thing.

Most modern post 1970 hydroplanes are rear engine design, and use the same type of V Drive gearbox as do rear engine displacements. In a straight line these are the fastest type of race boat, although with little in contact with the water they tend to take very wide turns, but in general turn better than most rear seat hydroplanes

Rear engine hydroplanes were the state of the art prior to about 1970, and many are still active in competition and in specific "classic hydroplane" classes.

Another type of what is under APBA rules a hydroplane is the Inboard Tunnel boat. These are pretty much the same idea as outboard tunnel boats, but are usually much heavily built to carry the weight of the inboard engine. These drive through a "stern drive" which is like the bottom part of an outboard engine, where the propellor turns with the unit and helps to push the boat around the corner.

Under APBA rules a hydroplane is any boat with 2 or more distinct planing areas with a step of more than 35mm. Before the development of the 3 pointer design in the 1950's, there was the Step Hydroplane. To the casual observer these looked like displacement boats. However out of the water they had several steps down the hull, much like the teeth of a saw blade. The object was to reduce the amount of the hull in contact with the water, as the boat rode on the tips of the teeth. Meaning less drag and more speed. There are presently none of this type of boat in competition today.

Keep in mind racers are always trying to gain a legitimate advantage and what is top of the heap today may be obsolete tomorrow.

Hydrofoils These are boats that ride on foils that stick down below the boat, and ride on those foils. Hydrofoils are prohibited from power boat competition