Everything you Need to Know About Marine Exhaust Systems

Everything You Need to Know About Marine Exhaust Systems

Introduction

Back in the 1970s, I got deeply involved in boat mechanics, and soon they became my passion. With over 25 years of experience and more than 300 diesel engine installs behind me, I've learned what it takes to build a reliable engine and powertrain system. A crucial component of this is the Marine Exhaust System.

My goal is to clarify the essential aspects of a successful marine experience by demystifying the Marine Exhaust System. Improper design, often influenced by misguided "couch engineering," is rampant in the boating industry. A fundamental principle to consider is "GRAVITY." The right initial setup can prevent many problems down the line. Remember, doing it right the first time saves money in the long run.

Since exhaust system design, fabrication, and installation have become a significant part of our business, it's time to share our insights from over two decades of work in this evolving field. For more information, visit our website.

First and Foremost

The two most basic issues to consider are:

1. Creating a safe system for the boat, on-board personnel, and the engine, which meets manufacturers’ requirements for back pressure and water entry.
2. Designing an exhaust setup that fits the boat while ensuring that water can never flood the engine, even if something goes wrong.

Poorly designed wet exhaust systems often lead to engine failures due to saltwater entering the engine. Ignoring basic principles like "GRAVITY," combined with amateur design efforts, frequently results in disaster.

Exhaust Size

When discussing exhaust sizes, it's important first to understand what the engine requires. Marine exhaust systems are typically "wet," comprising two parts: DRY and WET. Even in factory-supplied 90-degree "wet elbows," these two sections exist. The inner pipe of the "wet elbow" is usually a 90-degree dry bend, cooled by raw water.

EXHAUST SIZE boils down to two main rules:

1. Meeting engine requirements regarding total restriction (back pressure).
2. Designing a system that fits within the boat’s constraints.

If these rules aren't met, the exhaust system is the WRONG SIZE, as it won't meet engine specifications or fit the boat. The correct size of piping and mufflers ensures that exhaust flow doesn't build up to dangerous levels. Back pressure is measured in Water Column Height or Mercury (Hg), typically low (1.5” to 3” Hg).

Engine horsepower determines exhaust flow: more HP requires larger piping. Bends in the piping add to the length, affecting flow. For every 100 produced HP, the engine generates around 200 CFM of exhaust gases.

To meet back pressure requirements, a new specification from Cummins now allows a well-designed 5" WET system to meet the needs of QSB engines, making installation easier and less costly. Past experience helps, but engine specs or guides can also be used to select hose sizes.

Understanding Pipe, Tube, and Hose Dimensions

In this context:

• Pipe size is shown as a nominal size in SCH 10 wall.
• “Wet” size is the actual ID of the exhaust hose.
• Tube is measured by its OD (outer diameter), usually with a 1/8" wall.

Exhaust hose is always sized as an ID measurement to fit over a tube OD dimension.

Common Wet Exhaust Sizes

Based on over 300 installation reviews and exhaust tests, here are some common WET exhaust sizes that meet Cummins engines' requirements:

• 4" Tube, 4" Pipe Size & 5" WET Systems: For 200-250 HP engines.
• 6" WET Systems: For 300-500 HP engines. This size offers installation flexibility.
• 8" WET Systems: For 500-800 HP engines. This size is rarely needed under 500 HP.

Proper design and fabrication can meet exhaust restriction requirements with a mix of 4" dry, and 6" and 8" wet systems. Planning and eliminating unnecessary bends can lead to a cleaner, safer exhaust system.

Summary

A well-designed exhaust system significantly impacts engine room layout, safety, and functionality. Many disasters stem from poorly designed factory-type exhaust systems. Proper design ensures maintenance is feasible and prevents premature engine failures.

Marine Exhaust Systems play a crucial role in vessel construction. Correctly designed systems prevent safety issues, premature engine failures, and maintenance challenges. Considering the energy a diesel engine puts into the exhaust system, its design should be as robust as the powertrain.

We hope this information helps both buyers and builders in understanding and planning marine engine rooms. For more insights, visit MIC.

Everything You Need to Know About Marine Exhaust Hoses

When it comes to the complex systems that power marine vessels, certain components play a critical role in maintaining optimal performance and safety. One such component is the marine exhaust hose. Marine exhaust hoses are specially designed hoses used in marine applications to direct and remove exhaust gases generated by the engine. These hoses are integral parts of the exhaust system, ensuring the safe discharge of harmful emissions from the boat or ship.

• Heat Resistance: Marine exhaust hoses can withstand high temperatures, handling exhaust gases that range from 200 to 500 degrees Fahrenheit.
• Corrosion Resistance: Crafted from materials like EPDM or silicone, these hoses resist corrosion, saltwater, and other harsh elements.
• Flexibility and Durability: Designed to handle marine environments’ vibrations and movements, these hoses are highly flexible and durable.

Superiority Over Other Hose Types

Marine exhaust hoses offer several advantages:

• Safety: Engineered with multiple layers and insulation, these hoses handle high-temperature exhaust gases safely, reducing overheating, leaks, and fire hazards.
• Engine Performance: Proper exhaust flow reduces backpressure, enhancing engine efficiency, fuel economy, and longevity.

Materials Used

These hoses are typically made from high-quality materials such as EPDM, silicone, or Nitrile rubber, providing resistance to heat, corrosion, and chemicals.

Maintenance Tips

• Regular Inspections: Routinely check for wear, cracks, or leaks and replace damaged hoses immediately.
• Cleanliness: Keep hoses free from debris, grease, and oil build-up.
• Proper Installation: Follow manufacturer guidelines to ensure correct fittings, clamps, and connections.
• Replacement Interval: Replace hoses every five years or sooner if signs of deterioration are evident.

Marine exhaust hoses are essential for safely and efficiently expelling exhaust gases. Their resistance to high temperatures, corrosion, and flexibility make them superior to other hose types. If you're interested in learning more or placing an order, don’t hesitate to reach out. Our team at ASJ Industrial Hose and Fitting, located in Corona, California, is ready to assist. Give us a call today: (951) 735-1351.