Thunder on the River
Defiance OH - June 8-9, 2024
Welcome!
Three Rivers Outboard Racing Association is thrilled to return to Defiance, Ohio for Thunder on the River 2024. We are deeply appreciative for the support from the Defiance Main Street and Visitors Bureau to host this event on a beautiful waterfront racing location! Check out our daily schedule, learn more about APBA boat racing and follow along on the live broadcast presented by 24 Media!​!
What to Expect
NOTE: Once we begin racing we will proceed through the schedule as efficiently as possible. Our format of racing involves running 2 'heats' of a class, and the results of both heats are combined to finalize the results of the race. Drivers need to do well in both heats to finish well overall.
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Each heat begins with the announcement of a green flag which starts a 3 minute countdown clock. Boats are allowed to use the first 2 minutes to get started and on to the course, but in the final 60 seconds no more boats are permitted to enter the course. As the countdown continues, boats will begin to convene around the final turn towards the starting line. We utilize a 'flying start' where boats need to reach the starting line as the clock reaches 'zero'. If they arrive too early they are disqualified for starting too soon - and we say they 'jumped the gun'. Boats must maintain a straight line as they run for the start, or can be disqualified for a lane violation which creates a safety issue. Each heat is a sprint race of 3 laps, and we will race two heats of each class to finalize a race for that class.
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Common Flags:
Green Flag: Used to indicate the start of a 3 minute countdown, and during racing.
White Flag: Used to indicate the final 60 seconds before the start, or the last lap of the heat.
Blue/White Flag: Used to indicate a stopped boat or other obstacle is present on the course
Red Flag: Stop racing and watch for further instructions
Black Flag: Race Course is Closed - Return to the Pits
Checkered Flag: Race is Completed
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You may see a checkered flag pointed down at the end of a heat which indicates that boat was determined to have 'jumped the gun' and will be disqualified.
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Defiance "Thunder on the River" Daily Schedule
About the Categories and Classes
We are racing Junior, Stock and Modified categories under a sanction from the American Powerboat Association, and in all categories we have invited drivers for hydroplane and runabout style boats. Within each category there are a variety of classes for all sizes of drivers. In general, as the boats get larger so do the engines and the top speed increases.
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Hydroplanes vs Runabouts
Hydroplanes have a unique appearance and can be identified generally by having two distinct rounded noses on each front corner of the boat. These points are called sponsons and comprise the entrance of a tunnel under the center of the boat where the boat design allows air to funnel and compress under the boat. The result is hydroplanes tend to fly or float on the top of the water and are powered forward by the propeller from the engine in the back. At top speed only the propeller and sometimes the sponsons will be actively touching the water.
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Runabouts more closely resemble traditional fishing/pleasure boats with a flat or slightly rounded bottom, and have a single pointy nose aligned in the center of the front of the boat.
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Both runabouts and hydroplanes have a "turn fin" located on the left (or "port") side of the boat. This fin is used in the corners to help the driver keep the boat tracking through the corner. Without the turnfin the boat would slide out in the corners.
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Junior Category
Drivers aged 9-16 are able to run Junior Hydroplane and Junior Runabout classes. Powered by a restricted/detuned 15hp Mercury or Evinrude/Johnson fishing motor, these boats run about 40mph and serve as the training grounds to move to larger classes later. At 12 years old, junior drivers can run the fully tuned 15hp fishing motor in our AX hydroplane and runabout classes at speeds approaching 50-55 mph. Junior hydroplane/runabout classes have a minimum weight for the boat, motor and driver of 300lbs. The AX classes have a minimum weight of 325lbs for hydroplane and 330lbbs for runabout.
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Stock Category
Starting at 14 years of age drivers can race in the stock category in a variety of classes: where the classes move from smallest/lightest in the "A" classes up through progressively larger/faster classes designated by letters B, C and finally to D which are the largest/heaviest boats. In the stock category there are specific rules about the engine that control/limit modifications to keep complexity/cost down. The minimum weight for each class grows with the size of the boat/engine ranging from a minimum of 345 lbs for A Stock Hydroplane "ASH" up to 500lbs for D Stock Hydroplane.
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In the stock A and B categories you will see a purpose built racing outboard engine called a Sidewinder in 15 and 20 cubic inch varieties that will reach speeds of about 60 mph.
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In the C, 20ssh, and 300ssh classes a japanese built Yamato racing engine is featured, which is 30 cubic inches and will reach speeds of 65-67 mph.
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In the stock D classes a Mercury or Tohatsu engine of 44-50 cubic inches will reach speeds over 75mph.
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Modified Category
In the modified category, engine builders are allowed to modify the platforms used in the stock category to get better performance, and more speed. The letter system "A", "B", "C" and "D" are still used on several classes, and the category has some more exotic engines, including the 125MH "modified hydroplane" and 125MR "modified runabout" classes where the PRD Fireball Go-Kart racing engine has been modified to a racing outboard. The 125MH class will run about 60 mph and makes a nice entry class for new drivers and for junior drivers stepping up. Minimum weights range start at 345lbs in 125MH and increase with class sizes.
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In "B Mod" hydroplane/runabout and "C Mod" hydroplane/runabout classes you will see a longer exhaust pipe coming from the bakc of the boat. The driver has an extra handle in the boat that they can use to shorten or lengthen the exhaust pipe to the speed of the engine which dramatically increases performance. As the motor accelerates the driver will shorten the pipe and the experience is similar to a turbocharger on a car. B and C modified classes will approach 70mph
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In "D Mod" classes the engines get larger, the pipes get louder and the speeds approach 80 mph.
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The fastest boats in the modified category are Formula E "FEH" hydroplane and "FER" runabout classes where the boats can achieve speeds well over 80 mph.
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Other Information
All engines are two-stroke, gasoline engines - ranging from 87-90 octane 'recreational fuel for the junior and stock classes, and higher octane racing gasoline for higher compression engines.
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Two and three blade propellers are used in junior and stock classes, while four and sometimes five blade propellers are more commonly used in modified classes.
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Junior, stock and smaller modified classes have restrictions on the height of the motor in relation to the bottom of the boat, while larger modified boats have no restrictions and might have a propeller even or slightly above the bottom of the boat. Raising the propeller allows the engine to turn more freely and increases speed with the right setup.
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Drivers are required to wear safety gear including cut-proof kevlar pants and sleeves, a racing life jacket, and certified helmet.
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The boats are constructed of lightweight plywood, spruce or composite materials, and assembled with waterproof glues and epoxy. Junior class boats (without motor) weight about 80lbs and heavier "D Mod" boats can approach 140-160lbs while dry and without motor.