Marine exhaust systems are an important and often neglected engine of a ship. Most ships have a system of "wet" exhaust. The outlet for the exhaust gases from the exhaust manifold - the salt water is injected into the column. This mixture of gas and water is then passed through a series of curves to it from the boat, preferably in the back.
Exhaust fumes mixed with salt water to create a highly corrosive compound. This is why exhaust systems are often non-corrosiveComponents such as nitrile rubber reinforced hose (brown - not green - stripe), galvanized steel, fiberglass or plastic. The purpose of these components, which vary in size and shape depending on the size of the engine and the layout of the engine room is to prevent the engine hydraulicing. This occurs when an engine full of salt water that entered through the exhaust and can cause considerable damage if left for more than two hours. The water enters the exhaust gas to swell in the tail and armDrain design. In some sea conditions, such as by sea, the water can again be forced to exhaust when the engine is not running. Drains poorly designed, that water will flow back and fill the waterlock / muffler box then the hose in the exhaust manifold, exhaust valves and combustion chamber. With the engine full of water can not compress the engine crank over, it is not like water.
You will know that your engine is if you do not turn around hydrauliced -usually after a long period of sailing - and removing the starter and make sure it works. To remove remove water from inside the combustion chamber, first of all injectors, crank engine blowing over the water, replace vent injectors, injector lines and restart. Then leave the motor running until exhaust fixed.
Check that the mast is not coke up or corroded - a common problem. To check the exhaust riser remove the drain hose from the riser (often a difficult procedure)and look up the pipe to see if it is restricted by exhaust/salt build up. If build up is excessive the riser will have to be removed to check the engine end of the pipe. Coke can be scraped out to provide a short term fix although often the riser will have to be replaced. There are aftermarket systems which vary in quality. Make sure you fit the right design for the application.
Ensure your water-lock is low enough and big enough to hold all the water in exhaust system. Is there a gooseneck or central vertical loop in the exhaust hose at the transom exit? Is there a siphon break and is it functioning properly - no leaking valves?
Exhaust gas is poisonous and can cause sea sickness and headaches. Replace any faulty parts immediately. Use double hose clamps on each joint or, preferably, super clamps, bolt style, and exhaust cement if need be. Hot sections should be lagged with fiberglass tape to prevent burns.
Beware of asbestos lagging. Many older vessels and Marine engine installations had exhaust systems that were lagged with asbestos tape and rope. Asbestos was common in older boats noise.
Understanding A Marine Exhaust System