Marine Exhaust Systems - How They Function
byon 07-05-2012 at 05:43 PM (203 Views)
"Exhaust gases mixed with salt water develop a very corrosive compound. This is why exhaust systems are typically created making use of non-co...
Marine exhausts systems are an crucial and often overlooked element of a marine engine. Most vessels have a wet exhaust system. Salt water is injected at the riser the outlet for exhaust from the exhaust manifold. This mixture of exhaust gas and water is then passed by way of a series of bends until it exits the boat, preferably at the stern.
Exhaust gases mixed with salt water develop a extremely corrosive compound. This is why exhaust systems are frequently made using non-corrosive components 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 engine size and layout of the engine room, is to stop hydraulicing of the engine. This is brought on when an engine has filled with salt water which has entered through the exhaust and can result in extensive damage if left for far more than two hours. Water enters the exhaust from wave action at stern and poor exhaust style. In some ocean conditions, such as a following sea, water can be forced back up the exhaust when the engine is not running. Poorly designed exhausts permit water to flow back and fill the waterlock/muffler box then up the hose into the exhaust manifold, by way of the exhaust valves and into the combustion chamber. With the engine full of water the engine cannot crank more than as it is cannot compress water.
You will know your engine is hydrauliced if it will not turn more than normally after a long sailing period and you have removed the starter motor and ensured it works. To remove water from inside the combustion chambers, very first get rid of all injectors, crank engine more than to blow water out, refit injectors, bleed injector lines, and start off. Then leave motor running until exhaust sorted out.
Check to see that the riser is not coked up or corroded a widespread issue. To check the exhaust riser remove the exhaust hose from the riser (typically a difficult process) and look up the pipe to see if it is restricted by exhaust/salt build up. If develop up is excessive the riser will have to be removed to check the engine end of the pipe. Coke can be scraped out to supply a short term fix although usually the riser will have to be replaced. There are aftermarket systems which vary in high quality. Make sure you fit the correct design for the application.
Ensure your water-lock is low enough and huge enough to hold all the water in exhaust technique. 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 effectively 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 to have 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 had been lagged with asbestos tape and rope. Asbestos sound-proofing was also frequent in older boats. welding helmet"