Types of Marine Exhaust Systems - In Brief

Types of Marine Exhaust Systems &#; In Brief

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Dry Systems

A diesel exhaust system utilizing lagging (hard coating) or blankets  to keep the heat in the tunes in which the exhaust travels.  Water is sprayed in the exhaust gases at the mixer to cool the gasses.

Advantages

• Less risk of water intrusion into the engine
• Metalwork lasts longer as water is not retained  in the system

Disadvantages

• Takes up more space
• Higher surface temperature

Underwater Exhaust Systems

Exhaust system exits below the waterline. No main muffler is typically required, but does require an above water by-pass muffler. The system can be wet or dry. The exhaust exists through the stalk (the hole in the bottom of the vessel).

DeAngelo builds to the point of the stalk. Ship builder and/or the naval architect define the stalk location and hull penetration.

Advantages

• Quieter
• Smoke (soot) from exhaust passes through the water and is reduced
• No main muffler is required
• No exhaust fumes in boat

Disadvantages

• By pass requires additional hull penetration

Dry Stack Systems

A diesel exhaust system usually integrated in a tunnel in which the exhaust exits topside. Typically the design of choice for turbines. Normally found only in large yachts or commercial vessels.

Wet (Watercooled) Systems

Double tube system inwhich the inner tube carries the exhaust gases and the space between the inner and outer tube carries the water for cooling purposes. Water is sprayed into the exhaust gases at the mixer to cool the gases.

Advantages

• Cooler surface temperature
• Less space required
• Can be polished for asthetic purposes

Disadvantages

• More susceptible to corrosion due to holding water

Water Separation Systems

An exhaust system inwhich the water and cooled gas from the mixer are separated so they can be plumbed separately through the fibre-reinforced plastic (FRP) tubing to exit the vessel.

A water separation system normally exhausts through the hull.

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The same type system exhausting through stacks is called a cool stack system.

Contact DeAngelo Marine if you require an inspection / survey of your engine room, main engines or generator exhaust systems. We invite your inquiry for exhaust parts & accessories and exhaust repairs and service with your existing vessel. If you are in the design phase of new vessel construction or contemplating an engine overhaul, contact DeAngelo Marine Exhaust by or by : +1 954.763..

By Tom Burden, Last updated 6/25/

Water-cooled inboard engines inject cooling water into the exhaust pipe, which cools the exhaust and muffles engine noise. The exhaust then pushes the water out the exhaust pipe. This is known as a wet exhaust system. Wet exhaust systems have the advantage of using the heat-absorbing and sound-dampening qualities of water to cool and quiet the exhaust. Air-cooled, or dry exhaust, systems are uncommon except in performance powerboats or large work boats where excessive heat buildup and/or noise are tolerable, or in precisely engineered trawler/passagemaker exhaust systems which insulate the hot exhaust pipe with forced air.

Above- and below-waterline applications require distinctly different products to muffle engine noise. Powerboats use marine mufflers, commonly made out of non-metallic materials, to contain engine noise and cool the exhaust. Mufflers are always mounted above the waterline, and usually have some sort of check valve in-line to prevent backwards water flow, which might damage the engine.

Lift mufflers like Centek Vernalifts are used both by powerboats and sailboats. They are vertical mufflers mounted below the waterline with an outlet line coming off the top of the container. Exhaust gas and expended cooling water are mixed shortly after the exhaust manifold and travel together into the muffler's chamber where the cooling water collects before the exhaust gas pressure pushes it out the remainder of the exhaust hose. The mufflers's chamber also provides a place for seawater from following seas to collect if the boat is running under sail. For greater quieting, an inline muffler can be used downstream of a lift muffler.

Additional System Components

For vessels with through-the-transom exhaust, there are flapper valves that prevent following seas from running back up the exhaust system and flooding the engine. They clamp around the outside diameter of an exhaust pipe to form a check valve.

Exhaust hose or tubing is used to connect the exhaust manifold to the muffler and runs from the muffler overboard. It is essential to use material which can withstand heat, oil, acids, pressure, water weight and vibration without failure. As a rule of thumb, hose runs that are longer than four times the inside diameter of the hose should use wire-reinforced exhaust hose or fiberglass exhaust tubing. Shorter lengths can use non reinforced hose. All hose connections should be made to rigid surfaces (such as tubing, pipe, or the muffler itself); hose-to-hose connections are never recommended.

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