Boat Exhaust Flappers
– Inboard Ski/Wake boat exhaust systems are wet exhaust systems. During normal operation there is water in the exhaust pipes and muffler; the water is pumped first through your and into your engine. The hot engine water is then injected, at the aft end of the header, into the exhaust system. In other words, the water is injected into the exhaust system where the rubber hose begins. Without this water the rubber hose begins to smoke; in about 30 seconds.
When a boat engine is not running part of the the boat’s exhaust is flooded. All the exhaust system that is level with the exhaust outlets fills with water. On a Direct-Drive boat where the exhaust/muffler is in the floor, the entire muffler is typically flooded (that’s why it is important to have a good quality muffler). On a V-Drive the portion that is down low, at the bottom of the boat is flooded. When you start the engine the water that is flooding the exhaust system is blown out.
When the engine is running the exhaust system is filled with a mix of exhaust gasses (including Carbon Monoxide) and water.
Now, the reason for flappers. If you are heading down the lake fast, and your engine should suddenly die, the following wave, when it hits your transom, can push water into your exhaust system, and theoretically push water up into your engine. A flapper (or baffle) keeps this surge of water from pushing into the exhaust.
Now if your boat has curved downward exhaust tips, they will also prevent water from surging into the engine. Some boats with curved downward exhaust outlets do not have flappers, such as the Nautique Surf Pipe. Fresh Air Exhaust (FAE) provides the same protection as other curved down exhaust outlets.
For those that want the added peace of mind that a flapper provides, we offer them as an option. They are hidden under the rubber hose coupling that connects the FAE to the exhaust outlet. If you have an FAE that does not have any rubber hose couplings, the flapper will be covered by a stainless steel hose clamp.
– FAE has been installed on over 2300 boats. Water in the engine has NOT occurred as a result of FAE. Some boat engine installation instructions require a flapper; so if your boat’s engine is still under warranty, we recommend flappers just to prevent any conversation about any warranty issues that may arise. We know of NO warranty issues with FAE installed but we prefer to err on the side of caution. The flappers are optional and are built into the FAE; they do not change the ease of installation nor engine performance.