EXHAUST SYSTEM MAINTENANCE:
Often overlooked, exhaust
systems are an important aspect of any boat's maintenance
schedule. A few preliminary checks and regular care will not only save time but also prevent a costly repair bill. Unfortunately, many boat
owners pay little attention to their craft's exhaust
system - That is, until something goes wrong, and fumes and smoke billow into the boat
Note: See important SAFETY note and links at the end of this article.
Over time, heat, acids, corrosive gases, vibration, rust and seawater all play an active part in deteriorating an engine's exhaust. However, if corrosion
checks and maintenance are carefully carried out, exhaust systems can last up to 20 years.
The role of an exhaust system is to remove spent combustion gases away from the engine
. The by-products of this process are heat, vibration, fumes and, of course, noise
temperatures are usually high, water
is injected into the exhaust pipe, to mix and cool the gases. This mix and the resulting condensed solids (such as soot) are run through a silencer and a pipe, which exits overboard
. There are a number of practical aspects to be considered, which arise as a result of the engine's confinement in a boat's hull
As the engine is often deep below the waterline, the exhaust pipe must run at an angle to prevent any cooling water
running back directly to the hot engine. Such an occurrence can result in extensive engine damage. In the case of an engine placed below the waterline, water trap and drain devices are situated as close as possible to the engine. This prevents the water being sucked back.
water is also allowed to drain away.
In the case of an above waterline setup, vacuum valves are fitted in the exhaust line to avoid exhaust water being sucked back as the hot gases cool and contract
along the length of the pipe. Also, it must be arranged so that water cannot siphon back into the engine if the boat is heeled over while underway.
engine exhaust systems are generally designed to resist temperatures of not more than 120̊C. The exhaust gases, however, may reach more than 500̊C. To cool the gases, the exhaust cooling
system depends on a free flow of cooling water from the engine. This flow can drastically decrease, due to a lot of reasons such as a plastic bag or seaweed being sucked into the seacock under the keel
, or by a problem with the water pump
. The exhaust temperature will rise immediately to around 450̊C, the exhaust will overheat and may be seriously damaged.
Dry exhaust systems are less common than the wet system due to the fact components are more complicated and more costly.
In a dry system, the hot gases are led through a series of water-cooled exhaust jackets that surround the exhaust pipe. The water is sucked in from the river or sea by pump
, and once the heat from the exhaust pipe is 'exchanged' to the circulating water, it is then pumped overboard
Sometimes the heated water is run through a heater
or hot water system before being exited over the side.
With direct seawater cooling systems the temperature must be kept below 57̊C because the salt
solidifies inside the engine/exhaust components. It is important that the engine is run at the correct operating temperature to prevent this. Regular flushing
will help prevent this problem.
Vibration of solid mounted engines is a major culprit when it comes causing problems in exhaust systems — and thanks to other nuts, bolts and components that end up being shaken loose. If the exhaust gaskets break or leak as a result of this, the danger
of carbon monoxide poisoning is high.
* Check all bolted exhaust fittings on a regular basis and remember, the weight of the pipes must never be borne by the manifold itself. This can lead to a disastrous situation where leaks
and cracked manifolds result.
* The exhaust supports should be checked to ensure the pipe is supported at least every 4ft.
* Clamps should be doubled on flexible pipes and checked for loosening by vibration and corrosion
. The clamps on exhaust muffler
boxes are well known for freezing solid with rust. Keep them freed-up with heat-resistant graphite grease. And remember, a long run of exposed hot exhaust pipe must be insulated. The heat of a pipe is dangerous and allows excessive heat damage to woodwork, paint
, and in extreme cases can be a fire hazard. In addition overheated air in the engine compartment allows the engine to run hotter than normal and this results in inefficiency. Ensure adequate ventilation is supplied along the length of the exhaust run.
* Rubber perishes quickly in an overheated environment
. Check all hose clamps and double them on exhaust systems. The weakest link of the exhaust cooling system is the impeller of the engine-driven pump
. Always keep a spare. (there’s an easy access kit that allows you to change the impeller quickly and easily)
* Kinks and sharp turns and elbows should be avoided at all costs to prevent back pressure in the engine.
* If exhaust pipes have to run through bulkheads ensure the correct insulated type of metal fitting is used. Hot pipes can warp, crack damage and burn interiors.
* Large craft often have exhausts which exit overhead at the cabin
ends. It's easy to forget to inspect the pressure flaps for sticking or damage. It's surprising how much rainwater a three inch pipe will allow in. Once in, this water can corrode the bottom of the pipe.
Regular Check Ups
Thorough and regular checking and maintenance of your exhaust system will repay itself with saved cash dividends. On the other hand, a neglected exhaust system can be the source of smells, damage to interiors, components and a danger
Worse still, it can be a noisy, vibrating and life-threatening hazard that could result in fire and the total loss of your craft!
Carbon Monoxide (CO), the "silent killer"
, is a by-product created by engines through the combustion of carbon-based materials such as gasoline and diesel fuel
, kerosene, charcoal, and wood). When CO gas collects in an enclosed space it can become fatal, even if a person only breathes it in for a very short period of time!
“USCG - Checklist”
ALERT - FUEL
AND EXHAUST SYSTEM MAINTENANCE”
“USCG - Carbon Monoxide Hazards on Recreational Boats”