Marine Exhaust

 MER-Cowl Silencers

Silencer-Cowl Photo for blog

MER Stocks Cowl Marine Exhaust Silencers

 Cowl silencers turn obnoxious sound waves into heat and route the heat out with the exhaust gases. Available in many configurations and grades, the silencers are unsurpassed for sound attenuation.
Contact Bob or Norm at 800-777-0714 to order yours.
Specs-Cowl Silencer For Blog
Next Topic-Familiarization With Marine Exhaust Systems   

Every marine exhaust system must do three things well: Dispose of exhaust gases; reduce engine-room heat; and, make the engines as quiet as possible. 

Marine diesel engines develop an enormous amount of excess heat. A little less than 1/3 of every gallon of diesel fuel burned by a marine propulsion engine goes to turn the crankshaft and eventually the propeller— over 2/3 of the fuel turns into heat that must be disposed of as quickly as possible.  

To get the proper perspective on the amount of heat generated by a marine diesel engine on-board a fishing boat, consider the size of the heating unit in your home: A 100,000-British Thermal Unit (BTU) home heating system will heat a small home during cold weather; 1 gal. of No. 2 diesel fuel contains more than 130,000 BTUs of heat.  

Consider also a 42-ft salmon seiner with a 400-hp engine that burns 20 gal. fuel/hr running at full power. More than 2/3 the fuel—almost 2-million BTUs of heat/hr—is wasted as heat. 

The keel cooler transfers half this heat into the ocean, the engine’s exhaust system puts the other half into the atmosphere.  The hottest parts of the system are the exhaust manifold and turbocharger.  

Dry-wrapping manifolds and turbos helps control surface temperature with insulation that coats the exterior of the manifold and keeps heat from escaping into the engine room. Since it takes power to pump exhaust gases through the boat’s exhaust system, an engine with a dry-wrapped exhaust manifold can be slightly more efficient because the exhaust gas temperatures are higher, making them easier to pump. 

Water jacket-shielded systems—i.e., MER’s marine exhaust system for the 4024 & 5030 JOHN DEERE engines—are like a dry-wrapped manifold. They help reduce heat in the engine room while allowing exhaust gases to remain hot & easy to pump, maximizing engine & turbocharger efficiency.  

Water-jacketed exhaust manifolds—heavier & more expensive than dry-wrapped manifolds—absorb heat from the exhaust & transfer it to the engine cooling system. Exhaust gases cool a bit & make it harder for the engine to pump, reducing turbocharger efficiency & putting added load on the engine cooling system.  

Inside the Pipe–Wet or Dry? 
Although there are variations on marine exhaust system design, the choices come down to only 2—either a wet or dry exhaust. But now we’re talking about wet or dry inside the exhaust pipe, and sizing a silencer for such an application is a combination of art and science. 

Silencers and Mufflers On-board Fishing Vessels 
A dry-exhaust silencer is called a silencer, & a plastic or fiberglass muffler used in a wet-exhaust system is called a muffler. 

Exhaust silencers work by trapping & absorbing sound waves, turning them back into heat while restricting the flow of exhaust gases as little as possible. Steel or stainless-steel exhaust silencers come in several grades, the more corrosion-resistant steel & quieter grades costing more. 

Considerations When Sizing Exhaust Silencers: 
A-Cubic feet per minute (CFM) of exhaust gas coming out of the engine at its full-rated power and speed; 
B-Maximum exhaust gas temperature; 
C-Inside diameter & length of exhaust pipe; 
D-Number of bends in exhaust pipes & whether 45º or 90º, long radius or short; 
E-Level of silencing desired; and, finally, 
F-Available space for installation. 

When Stewart Everest of Everest Marine & Ian Jefferds of Penn Cove Shellfish designed their 4th shellfish-harvesting vessel, the 63-ft Mytilus, they again specified JOHN DEERE engines from MER Equipment. The original plans called for a wet-exhaust system to exit the stern, but Stew was very concerned about reducing exhaust noise for the sake of the crew as well as those on shore, often operating near populated shorelines. 

MER President Bob Allen persuaded Stew to instead go with a specially configured dry-exhaust system exiting through a vertical stack. Stew was concerned about added weight high-up on the boat.” “However, after the marine architect stability was very good, we took Bob’s advice & went for the vertical stacks.” 

Bob’s plan called for wrapped Cowl silencers in the engine room with 5-in.-diameter openings in & out, adding two 5-in., 90º elbows 3 feet downstream of the Cowl silencer to further absorb sound. Finally, near the far extremity of the 20-ft system just 6 feet from the end, they installed EM critical-grade in-line silencers with 5-in.-openings, exiting with 6-in. pipe. It’s worth mentioning that Cowl & EM both make air-intake silencers for installing on an engine’s air-intake side, which can really make a difference in the engine-room noise level. 

Stew says he always lines enclosures housing the exhaust components with Barrier 104—his favorite sound-attenuation product—in either 3/4” or 11/4” thicknesses. 

When starting the engines Stew found the silence was … deafening! With the mussel-processing deck directly above the engine room, Stew wanted to keep the work area very quiet. Going with the vertical exhaust rather than the original wet exhaust meant two stacks with outlets above the top house. The black EM-silencer house out of the weather. Stewart put sound-deadening material in these cavities where the EM silencers were fitted. 

I wouldn’t have thought engines could be this quiet!” Stew Everest, Everest Marine MER’s Cowl-EM silencers on the latest mussel harvester in the Penn Cove Shellfish fleet. All 4 powered by MER JOHN DEERES, the first 3 have 6081s, this one–twin 6068s “We had to turn off the radios in the wheelhouse to hear if the engines were running.” Penn Cove Shellfish owner Ian Jefferds, says, “Running DEERES with MER’s exhaust system, the sound reduction far exceeded our expectations.” 

Art work from Practical Boat Mechanics B.L.E.   Rain Exclusion Is One Important Consideration

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