Unlimited Hydroplane is the world’s fastest racing boat

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A modern Unlimited Hydroplane is the world’s fastest racing boat, capable of speeds in excess of 200 mph. It represents the product of over 100 years of evolution in race boat design and incorporates the most powerful engines, most advanced construction techniques and the best safety systems available in boat racing today. All Unlimited Hydroplanes are a “three point” design, meaning they are designed to only touch the water at three points when racing: at the rear of the two front “sponsons” (the projections of the hull in front of the driver cockpit), and the propeller at the rear of the boat. “Runners” under the sponsons and “shoes” at the rear of the boat are generally all that touch the water during race conditions.

A modern Unlimited is made of aluminum, fiberglass, carbon fiber and graphite composites, and weighs a minimum of 6750 pounds in race trim. The boats are between 28 and 32 feet long, 12 to 14 1/2 feet wide and about seven feet from the bottom of the rudder to the top of the rear wing. Driver safety is paramount in the design and operation of an Unlimited, so the boats have a number of systems designed to keep the driver safe in the case of an accident. The fully enclosed cockpit is the primary safety feature, incorporating a full interior roll cage that is bonded to the cockpit shell to maintain the integrity of the driver area. The windows are cut from the canopy of F-16 fighter jets, giving the driver ultimate protection, yet allowing him to see clearly. Five point quick-release harnesses are used to keep the driver strapped into the seat and an escape hatch is built into the floor of the cockpit to allow the driver to escape if the hydroplane flips and lands upside down. Every driver is required to wear a certified helmet and a HANS device for head and neck protection. He also wears a mask that incorporates an on-board air supply that allows him to breathe in case the cockpit fills with water, but also lets him communicate via the onboard radio.

A “Rotor Burst protection System” (RBPS) is in place around the “hot end” of the engine to contain the fragments in case of a catastrophic failure of the turbine’s power rotor. All of today’s unlimited hydroplanes are powered by a single Lycoming T-55 L-7 turbine engine that once powered our military’s Chinook helicopters from as far back as the Vietnam War. The turbine is capable of outputs of around 3000 HP and runs on Jet-A (kerosene) fuel. The large tail pipe in the back of the boat is only to allow heat to exit; no thrust is created from the exhaust.

The engine’s output is hooked to a “gearbox” that has a single adjustable gear ratio that reduces the engine speed to the appropriate output shaft speed to make the propeller work most efficiently. A “long shaft” transfers the gearbox output through the bottom of the boat to the “strut” where the “short shaft” connects to it with a coupler. The short shaft has the propeller connected to the end and it allows the prop to be easily removed after every heat for inspection.

There is a fixed wing on the rear of the boat that can only be adjusted when in the pit area. This wing is only used for stabilizing and trimming the boat so that very little of the boat’s rear running surfaces touch the water. The second wing on the boat is located at the front of the “pickle fork” nose. Unlike the rear wing, this “canard” is actually controlled during racing by the driver via foot pedals. The canard allows the driver to more easily “fly” the boat, pushing the rear of the canard down to create lift and raise the nose of the boat, or raising it to lower the nose of the boat if it gets too high and is in danger of “blowing over”. The driver will also manipulate the canard in the turns or when rough water and windy conditions persist.

The large “cowling” behind the driver cockpit functions as an aerodynamic device and as a “scoop” to funnel intake air to the engine. The rear of the cowling is vented to allow for excess air to pass through so as not to trap air that would otherwise slow the boat down. During saltwater races, an additional extension to the cowling may be used to prevent saltwater from being ingested into the engine. Excessive saltwater ingestion will almost instantly reduce engine output due to the buildup of salt residue on the turbine blades. This buildup effectively changes the compression ratio of the engine, allowing for “pre-ignition” (like a backfire on an automotive engine) that will shoot large flames out of the back of the engine (see image at right), and can even damage an engine.

A single three blade, 16″ diameter propeller is allowed. Ideally, only one propeller blade should be touching the water when at racing speeds. Different pitch propellers are chosen for use based on course length, conditions and starting position. Race props can cost in excess of $15,000.The prop creates the distinctive “roostertail” behind the boat, raising literally tons of water into the air for up to 300 feet behind the boat.

The skidfin is a large metal fin that is attached to the area at the rear of the left sponson that allows the boat to “dig in” and make a turn without skipping across the water. The wall of water the skidfin throws up in the corner is one of the most spectacular sights in boat racing, reaching heights of nearly 50 feet and extending for 6-7 boat lengths behind the boat.

The rudder is a relatively small metal blade that is located in a bracket extending from the transom at the right rear of the boat that acts to steer the boat through the corners. The rudder only becomes truly effective at higher race speeds and makes maneuvering at low speeds somewhat challenging. A water pickup at the base of the rudder feeds onboard cooling and lubrication systems.

All Unlimiteds carry onboard digital recording devices that capture different streams of data, from engine speeds and fuel flow to wing angles and temperatures. All turbine engines are limited to 4.1 gallons per minute fuel flow and less than 115% “N2” speed. N2 speed is a pre-determined upper RPM limit that the engine cannot exceed for more than five seconds. The data recorders log these two critical data streams and are reviewed by officials at the end of every qualifying attempt and heat. Fuel flow and N2 violations will void a qualifying speed and will disqualify a boat from the Heat in which violation occurs.