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Old 25-10-2012, 08:16   #76
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Re: Retirement age of a diesel engine

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Originally Posted by Bluewaters2812 View Post
I subscribe to the notion that diesel engines hate midweek club-racers that fire them up to get them out of the marina to be switched off for an hour or two's sail-racing and then banged back on to get into harbour and moor the boat up only to be switched off again.

Go cruiser/live-aboards ... I am a diesel engine ... use me properly!
The much-maligned Atomic 4 gas inboard (low-compression, simple design, eats a tank per season if you are not doing 50 miles of motoring) is actually a more sensible choice for a race boat, at least up to 35 feet or so. You can turn it on and off all day or until you drain your batteries and the net wear is nearly the same as a long run.

But marketing and "modernity" made the purchase of the right engine for the wrong job (10 minute dashes) the rule of thumb.

The funny thing is that small electric engines on race boats make the most sense. You could run them on four Group 31s either side of the mast and have a light "electric wheel" to push you to and from the line and it would STILL weigh less than a diesel, a small fuel tank and two Group 27s, as is common, and the batteries would be right below the center of effort!
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Old 25-10-2012, 08:25   #77
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Re: Retirement age of a diesel engine

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I agree and run mine the same way!

Hell I don't even know what 80% load on my engine is. I run mine based on sound, it is pretty apparent from the sound where the engine is most happy at. But run it up hard a few times every few hours and allow it it cool down prior to shutting down.

I think that other than operating your engine corrently and changing the oil etc that how long the engine lasts comes down to luck! On my engine the luck line lines up with the 20,000 hour mark I hope.
Diesels have something called a "power curve" or something similar listed in their manuals. They tail off and flatten near the top of the curve, so to find 80% for your model, you find where the curve crosses the "80" with the associated RPM. It might be 2,100 RPM or 2,600 RPM if somewhere past 3000 RPM is the maximum.

Maximum revs are fine for stopping in the shortest distance, but generally is neither fuel nor thrust-efficient, given that those last few hundred RPMs do not add a lot of thrust.

Of equal if not more interest is the other chart you'll likely see for your engine, which relates fuel consumption to RPM for (assumed) flat water. This is going to be less than 80% in most cases, but well above 50%.

If you plan on motorsailing, this is the sweet spot for range and economy. The surprising thing for most people who motor sailboats for longer distances is that the difference between fuel consumption at, say, 5.2 and 5.5 knots can be quite significant. You soon learn where the engine's thrist, your personal time and wallet factors, and the RPM readings intersect.
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Old 30-10-2012, 11:42   #78
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Re: Retirement Age of a Diesel Engine

..... Speaking oif reading the manual, has anyone got a site where they have found one for the Lehmans? Such as the 90hp - we think?!? Thanks ~
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Old 13-01-2013, 19:29   #79
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Re: Retirement Age of a Diesel Engine

Diesel engines actually run cooler than most gas engines. The temperatures in the combustion chamber are much lower than those in a gas engine, also the combustion byproducts of diesel fuel are much less corrosive than gas engines. They also tend to run at much lower RPM's than gas motors, RPM's are a killer of crank bearings as well as piston walls, the loads on the crank increase dramatically with RPM.
The reason diesels last so long is the nature of the fuel as well as the low RPM nature of most diesel engines, also diesel fuel is more of a lubricant than gas.
The engines are also built more heavily than most gas engines due to the commercial nature of most diesel applications. I've built offshore gas engines as well as diesels over the years, and know how much more work is required to make gas engines last.
Maintenance is the key, oil changes, proper running, and clean fuel will go a long way.
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Old 14-01-2013, 01:14   #80
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Re: Retirement Age of a Diesel Engine

I guess that just like humans, diesel engines "retire" at a great variable age, dependent on abuse lol. No doubt they are designed with longevity in mind but then again there are enough people out there who will intentionally or unwittingly ensure that the lifespan is curtailed to a point way within the potential lifespan.
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Old 14-01-2013, 02:07   #81
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Re: Retirement Age of a Diesel Engine

From my experience as a marine engineer in commercial shipping:
Times to overhaul.
Slow speed ( max 130 RPM) 2 stroke engine above 10 000 hp: overhaul every 40 000 - 50 000 hours
Medium speed (max 1000 RPM) every 30 000 - 40 000 hours.
High speed engine ( standard truck engine 1500 - 2500 rpm) every 20 000 - 25 000 hours

Off course there are small overhauls in between for faster wearing parts such as fuel pumps and injectors.

An engine can last forever if the parts are available and the liners can be replaced. Some small engines like cars don't have replaceable cylinder liners and thus have a limited lifetime.
However overhauling can damage an engine after a while pipes start leaking and so on. Usually in commercial shipping a high speed genset engine is replaced after 20-30 years and up too 150 000 hours.

As for my sailboat.
SABB type G 10 hp engine is 51 years old and has 32 000 hours on it.
But it has had 2 major overhauls where all bearings, the liner and the head where replaced. (the head has been replaced 3 times because of leaking valves) I don't know how this engine was run by the previous owner but I do have the maintenance logs.
Since the parts are still available I will keep it as long as possible.
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