Marine Exhaust System How They Work

Marine Exhaust System How They Work



Marine exhausts systems are an​ important and​ often overlooked part 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 through a​ series of​ bends until it​ exits the​ boat, preferably at​ the​ stern.

Exhaust gases mixed with salt water create a​ highly corrosive compound. This is​ why exhaust systems are commonly 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​ prevent hydraulicing of​ the​ engine. This is​ caused when an​ engine has filled with salt water which has entered via the​ exhaust and​ can cause extensive damage if​ left for​ more than two hours. Water enters the​ exhaust from wave action at​ stern and​ poor exhaust design. 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 allow water to​ flow back and​ fill the​ waterlock/muffler box then up the​ hose into the​ exhaust manifold, through the​ exhaust valves and​ into the​ combustion chamber. With the​ engine full of​ water the​ engine cannot crank over as​ it​ is​ cannot compress water.

You will know your engine is​ hydrauliced if​ it​ will not turn over – generally after a​ long sailing period – and​ you have removed the​ starter motor and​ ensured it​ works. to​ remove water from inside the​ combustion chambers, first remove all injectors, crank engine over to​ blow water out, refit injectors, bleed injector lines, and​ start. Then leave motor running until exhaust sorted out.

Check to​ see that the​ riser is​ not coked up or​ corroded – a​ common problem. to​ check the​ exhaust riser remove the​ exhaust 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 sound-proofing was also common in​ older boats.




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