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Diesel Question for big boats

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Old 05-23-2006, 07:36 PM
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Default Diesel Question for big boats

I recently learned they have both 2-stroke and 4-stroke diesels used in large fishing boats (50'+). Are these the same 4 and 2-stroke terms as as used in gas motors and what are the pluses and minuses of each? BTW -- I am taliking about the 1000+hp engines.
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Old 05-23-2006, 07:39 PM
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Default Re: Diesel Question for big boats

The old Detroit's are two stroke. I think most of the newer large diesels like MANN and MTU ect are four stroke.
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Old 05-25-2006, 12:41 AM
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Default Re: Diesel Question for big boats

ttt
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Old 05-25-2006, 12:44 AM
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Default Re: Diesel Question for big boats

no more 2 stroke diesels. i havnt seen or heard of them in ages. dotn think i ever met somone that still had them. now most are common-rail also.
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Old 05-25-2006, 08:15 AM
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Default Re: Diesel Question for big boats

Theres still a lot of old Detroits out there...making sweet sounds for a diesel!
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Old 05-25-2006, 08:38 AM
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Default Re: Diesel Question for big boats

Big difference in the 2 stroke and 4 stroke diesels...alot less noise less smoke less smell in the 4 stroke. you will find them, on newer boats within the past 3-5 years you will also see some 4 stroke diesels on some refits as well.
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Old 05-25-2006, 08:46 AM
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Default Re: Diesel Question for big boats

I have 8v92 DDA's in my Bertram. They are two stroke motors. You will find two strokers in boats up till the late 90's & a few scattered ones in later models. I just ran from Florida to CT with another boat (1996 Hatteras) with 12v92's. He said that boat was the last of the 12v92 series for Hatteras.
As far as smoke, both of my engines are fresh (with less than 150hrs) and aside of a very slight puff right at start up, there is no smoke or smell.
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Old 05-25-2006, 09:02 AM
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Default Re: Diesel Question for big boats

The really LARGE displacement engines (ship engines that run ~250 rpm and less) are two strokes. The advantage here is a power stoke every crank revolution. Make half the power but at once per revolution as opposed to a four-stroke making power every TWO revolutions (therefore approx the same power as a four-stroke). This allows the crank to "see" less magnitude of torsional pulses but at twice the frequency. In essence, the torsionals in the crank are "flat", not cyclical loading and unloading of a large mass resulting in less fatigue.
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Old 05-25-2006, 01:18 PM
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Default Re: Diesel Question for big boats

Most of these "smaller" diesels are now 4 strokes. They used to be two stroke, but man, those went out long ago. These were different from a two stroke gas (saw or trimmer) engine. The small gas engines use the crank case to compress the air fuel mixture. The two stroke diesels were using GMC type superchargers for the compression. This also kept the oil out of the air. Having oil mixed with the air on a diesel wouldn't be a good thing. More than one diesel has run away due to poor oil control. The original x:71 series superchargers came off two stroke diesels. You can still find them on ebay and people are sucker enough to buy them. Most of the inline blowers are long gone leaving only the V type superchargers. The V blowers have no performance potential.
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