Types of Hulls - Flatbottom or Hydroplane
There are 2 typical styles of raceboats. Flatbottoms or hydroplanes. 
Flatbottoms are like your conventional V shaped hull. The very early style of flatbottom boats had 'steps' built into the bottom, to lift the bottom up onto these steps and create less water resistance. They were also called hydroplanes. Today, many of the faster production type hulls have 'steps' built into the bottom. 
Three point hydroplanes were developed after Ventnor Boat Works patented their idea of attaching water skis to the outside of the conventional hull to plane the bottom of the hull off the water. The idea was started while building suicide boats for the Chinese government. They required a fast boat with a 500 lb. bomb in the bow. All that weight in the bow was hampering the boat's design. Ventnor also built waterskis and the idea came about to strap a pair of skis unto the bow to carry the weight started the hydroplane evolution. Years later, Ted Jones developed the 3 point hydroplane after WWII which had sponsons attached to basically a hull that resembled an aircraft wing. This 3 point hydroplane flew over the water on a cushion of air, balanced by it's sponsons and prop. The world water speed records at that time were literally smashed by this new style of racing hull.

Brief History - Why are hydroplanes constructed like they are?:
Since their inception and for the most part, the vintage inboard hydroplanes featured throughout this website had their frames built from solid wood framing. Typically, the framing is milled from Sitka Spruce. This wood specie is also used in airplane construction. Mainly because of it's strength to weight ratio. The hydroplane's framing (or 'skeleton') has a plywood "skin" attached to it and encapsulating the framing. The glues used back then were no where near as good as the adhesives used today. Varnish was used to seal all the wood and plywood. Today's raceboat are built basically somewhat the same. But the newer, high tech construction materials available to a raceboat builder is much more extensive. High strength adhesives, lightweight materials and coating materials have these boats much lighter than there forefathers. They are still finely crafted machines. As they were in the past, each one built for speed -- is truly, a work of art! 

I have written a more in-depth 5-part story, titled The Vintage Builder's Guide on the makers of vintage hydroplanes on the Phil Kunz Photography website. As you read through this article, the work is surrounded by Mr. Kunz's camera work, as we post one representative hydroplane built from most of the designer/builders of the classic hydroplane era.

Going fast on water
Hydroplanes were designed and built for speed. Their lightweight hulls were designed to fly on a cushion of air and plane the hydro above the water with only the propeller, rudder, and the runners of their two rear sponsons making contact with the water. This is why they are sometimes called, 3-point hydroplanes. There is also a skid fin that is placed on the port side sponsons to "skid" the hydroplanes into the turns. The raceboats always competed on a circular shaped race course and always go counterclockwise. Hydroplane designers learned the less resistance to water, the faster they would go. They even discovered that having only one half of the propeller in the water, increased the boat's speed. The term --- Prop Rider's --- came into play. The motors are directly coupled to either a gearbox or the propeller shaft. Depending on the motor's rotation, you will see the hydroplane's propshaft being driven either off of the flywheel, or with the motor being placed backward in the boat, off the front of the crank. Since the was no need for a transmission, most hydros have you starting the motor and you're underway! And you want to be underway because hydroplanes typically don't use water pumps for motor cooling. They use water pickup tubes that force feed water into the engine for cooling. Most raceboats also force fed water to cool the gearbox, motor oil cooler, prop shaft bearing etc. All kinds of methods were developed to make the boats go faster and be as reliable as possible to win the race. With either Hydros or Flatbottoms, each class would be changing motors as new ones were developed and released to the public. They keep just getting faster and faster in competition.

General information on different classes of limited inboard raceboats:
The different limited classes of raceboats were based on cubic inches, cubic centimeters, or litres of total engine displacement. Most classes would typically have length and weight limits. They are either stock or modified classes. Some of the inboard limited racing classes throughout this era were the following cubic inch classes: 48, 72, 91, 135, 136, 145, 150, 225/226, 266, 280, and 7-litre. Classes, motor sizes, lengths, and weights would change as new engines were introduced. Information on the racing classes of the APBA and their evolution into today's classes is on the Phil Kunz Photography website. His section on all the limited-class inboard hydroplane and flatbottom classes is second to none. And his book, released in 2004, Prop Riders - 60 Years of Racing Hydroplanes is the most comprehensive work ever compiled on this subject. 

Junior Gold Cup Hydroplanes:
The largest limited class, after WWII up to the early 1970's, were the 7-litre modified class (427 cu. in.). This class of hydros used the "big block" engines of their days. The world straightaway speed record for 7-litre class hydroplanes is held by George "Buddy" Byers, owner/driver of CHRYSLER QUEEN H-1  at 168.2 mph. That record was set with a supercharged Hemi.
In 1970, the APBA added a stock class with those boats running under the letter prefix - J. The J and H classes evolved into the "Grand National Hydro" (GNH) and "Grand Prix" (GP). Another class that evolved were the "Unlimited Lights" (UL).

Unlimited Hydroplanes:
The largest class of hydroplanes are the unlimited's. They were called the "Thunderboats" when they ran piston powered, supercharged, 12 & 16 cylinder, airplane engines that were manufactured by Allison (GM)  & Rolls Royce (British). Nowadays, they mostly run a turbine engine. There are numerous pages on the internet devoted to this division.