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Author Topic:   Re-Powering with Outboard: Noise Level

Paul in HK posted 10-21-2006 12:10 AM ET (US)
I have a Four Winns 315 Express with twin diesel sterndrives: two 205-HP OMC Cobra diesels. They are hard to service in Hong Kong, so I`ve made a decision to re-engine with two 250-HP outboards.
Which is better: 250-HP OptiMax (two-stroke) or a four-stroke? Noise is a big factor for me. Any views?
pineapplepig posted 10-21-2006 06:14 AM ET (US)
If noise is the main issue, then whilst the new (2007) Optimax is definitely quieter than the screamingly loud earler models, it is still no match for either a four-stroke or an E-TEC. So if your only choice were OptiMax or a four-stroke, and noise was your major concern, then four-stroke motors would have to be the way forward for you, IMO.
jimh posted 10-21-2006 09:57 AM ET (US)
In February of 2006 Mercury announced it would have a new generation of the OptiMax motor available, the OPTIMAX THE NEXT GENERATION motor (OTNG). One of the improvements promised with the new motor was reduction in sound levels. The promised reduction in sound levels has only been described as "up to six decibels."
I appreciate that six decibels is a noticeable reduction in sound level, but the OptiMax motors are so much louder than most other modern outboard motors that reducing their sound level by 6-dB may not be enough. In a test conducted by independent testers (BASS & WALLEYE BOAT MAGAZINE), the OptiMax motor was found to be the loudest 250-HP motor tested.
For more information on the OPTIMAX THE NEXT GENERATION motor, see:
http://continuouswave.com/ubb/Forum1/HTML/011847.html
For more information about the sound levels of the OptiMax compared to four-stroke motors, see my comments in the long discussion about the 250-HP engine test results in
http://continuouswave.com/ubb/Forum1/HTML/012548.html
As this was a very long discussion, let me repeat a portion of it here which applies to sound levels:

quote:
More on engine noise:
At idle the Optimax has a measure sound pressure of 75 dBa compared to a Verado at 56 dBa. That is a difference of 19-dB. To put this difference into perspective you could think of it this way:
Suppose you were at a large gathering of 65 boats. You are standing equidistant from all of the boats. It is a quiet morning. The boats begin to start their engines.
The first boat to start is a Verado. His engine produces 56-dBa of sound. A second Verado boat starts up. The two Verado boats make twice as much sound, or a 3-dB increase, so now there is 59-dBa of sound. Two more start up, another 3-dB increase, so now there is 62-dBa of sound from the four engines running. Four more Verado engine start, and the sound jumps to 65-dBa.
There are eight Verado engine running. Eight more start. The sound level increases 3-dB to 68-dBa. There are now 16 Verado engines running. Another 16 Verado engines start, and the sound increases 3-dB to 71-dBa. We now have 32 Verado engines running. The remaining 32 Verado engines start. The sound level doubles again, and we arrive at the total sound level for 64 Verado engines: 74-dBa.
Finally, the lone OptiMax engine in the group starts up. His engine alone produces 75-dBa of sound. In other words, one OptiMax engine at idle makes more sound than 64 Verado engines at idle.
This is not a fanciful invention. It comes directly from the test results.
This should give you an idea of how much difference there is in the sound level between the OptiMax and the quietest four-stroke motors. Even if the OTNG motor succeeds in reaching its goal of a reduction in sound level of "up to six decibels", it will still be significantly louder than the quieter four-stroke motors.
The OptiMax motor has demonstrated very strong performance, with excellent acceleration, top speed, and fuel economy. Its Achilles' heel, however, is its sound levels.
deepwater posted 10-21-2006 06:14 PM ET (US)
Just who are you trying to sneak up on ^@^,,,Twin 250s ,,I like the wine

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Author	Topic: Re-Powering with Outboard: Noise Level
Paul in HK	posted 10-21-2006 12:10 AM ET (US) I have a Four Winns 315 Express with twin diesel sterndrives: two 205-HP OMC Cobra diesels. They are hard to service in Hong Kong, so I`ve made a decision to re-engine with two 250-HP outboards. Which is better: 250-HP OptiMax (two-stroke) or a four-stroke? Noise is a big factor for me. Any views?
pineapplepig	posted 10-21-2006 06:14 AM ET (US) If noise is the main issue, then whilst the new (2007) Optimax is definitely quieter than the screamingly loud earler models, it is still no match for either a four-stroke or an E-TEC. So if your only choice were OptiMax or a four-stroke, and noise was your major concern, then four-stroke motors would have to be the way forward for you, IMO.
jimh	posted 10-21-2006 09:57 AM ET (US) In February of 2006 Mercury announced it would have a new generation of the OptiMax motor available, the OPTIMAX THE NEXT GENERATION motor (OTNG). One of the improvements promised with the new motor was reduction in sound levels. The promised reduction in sound levels has only been described as "up to six decibels." I appreciate that six decibels is a noticeable reduction in sound level, but the OptiMax motors are so much louder than most other modern outboard motors that reducing their sound level by 6-dB may not be enough. In a test conducted by independent testers (BASS & WALLEYE BOAT MAGAZINE), the OptiMax motor was found to be the loudest 250-HP motor tested. For more information on the OPTIMAX THE NEXT GENERATION motor, see: http://continuouswave.com/ubb/Forum1/HTML/011847.html For more information about the sound levels of the OptiMax compared to four-stroke motors, see my comments in the long discussion about the 250-HP engine test results in http://continuouswave.com/ubb/Forum1/HTML/012548.html As this was a very long discussion, let me repeat a portion of it here which applies to sound levels: quote: More on engine noise: At idle the Optimax has a measure sound pressure of 75 dBa compared to a Verado at 56 dBa. That is a difference of 19-dB. To put this difference into perspective you could think of it this way: Suppose you were at a large gathering of 65 boats. You are standing equidistant from all of the boats. It is a quiet morning. The boats begin to start their engines. The first boat to start is a Verado. His engine produces 56-dBa of sound. A second Verado boat starts up. The two Verado boats make twice as much sound, or a 3-dB increase, so now there is 59-dBa of sound. Two more start up, another 3-dB increase, so now there is 62-dBa of sound from the four engines running. Four more Verado engine start, and the sound jumps to 65-dBa. There are eight Verado engine running. Eight more start. The sound level increases 3-dB to 68-dBa. There are now 16 Verado engines running. Another 16 Verado engines start, and the sound increases 3-dB to 71-dBa. We now have 32 Verado engines running. The remaining 32 Verado engines start. The sound level doubles again, and we arrive at the total sound level for 64 Verado engines: 74-dBa. Finally, the lone OptiMax engine in the group starts up. His engine alone produces 75-dBa of sound. In other words, one OptiMax engine at idle makes more sound than 64 Verado engines at idle. This is not a fanciful invention. It comes directly from the test results. This should give you an idea of how much difference there is in the sound level between the OptiMax and the quietest four-stroke motors. Even if the OTNG motor succeeds in reaching its goal of a reduction in sound level of "up to six decibels", it will still be significantly louder than the quieter four-stroke motors. The OptiMax motor has demonstrated very strong performance, with excellent acceleration, top speed, and fuel economy. Its Achilles' heel, however, is its sound levels.
deepwater	posted 10-21-2006 06:14 PM ET (US) Just who are you trying to sneak up on ^@^,,,Twin 250s ,,I like the wine