Car/boat engine life - how to calculate ???

Loggo

Loggo

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These days we expect our cars to cover well in excess of 150,000 + miles in a lifetime.
How does this translate into boat engine hours ? I see a lot of boats around 10-15 years old with engine hours of 1000-1500.
Assume a car averages 40 MPH then 1500 hours would be 60,000 miles - around 30% of it's life.
Can I therefore believe that my 1,450 hour engine will outlive the hull :)
or I am I fooling myself ? :rolleyes:

Does anyone have any thoughts on this - how many hours can we expect an engine to last ??
 
Loggo said:
These days we expect our cars to cover well in excess of 150,000 + miles in a lifetime.
How does this translate into boat engine hours ? I see a lot of boats around 10-15 years old with engine hours of 1000-1500.
Assume a car averages 40 MPH then 1500 hours would be 60,000 miles - around 30% of it's life.
Can I therefore believe that my 1,450 hour engine will outlive the hull :)
or I am I fooling myself ? :rolleyes:

Does anyone have any thoughts on this - how many hours can we expect an engine to last ??
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Most car engines run at very low powers for most of the time. Cruising a Mondeo/Golf/Vectra at 70mph on the motorway probably takes 40hp or so - though there will probably be two, or three, or four, or five times that available. driving around town takes even less - I have a car with a 26hp engine which keeps up with traffic in town just fine.

Boat engines, on the other hand, spend much of their lives at much higher proportions of maximum power, and at fairly constant revs too. Hence much lower lives. It's the same with aircraft, and particularly with glider tugs, which spend half their lives at full power and half being shock cooled with the fastest descent the pilot dares to make.
 
There's no particular reason why a freshwater cooled marine diesel should expire before 5000 hours. This probably doesn't apply to some of the newer, automotive derived units such as the D3, which are great while they work, but a bit disposable.

But most expire before then for all sort of peripheral reasons, cooling / gasket / injection problems that aren't nipped in the bud, salt water ingress, failing outdrives etc.
 
2CV ? - could be a Dyane - I did 60k miles in three years in one of thse in the 90's However, I am thinking of a river situation, doing maybe 1500 RPM, can I not expect a few more hours ??
 
Ubergeekian said:
Boat engines, on the other hand, spend much of their lives at much higher proportions of maximum power, and at fairly constant revs too. Hence much lower lives. .
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Thats true also of industrial engines in things like construction machines and generators; they also spend most of their working lives at near max power. These engines might last 10,000 hours or more. The key difference between pleasure boat engines and industrial engines (which are often closely related) is that pleasure boat engines are usually offered at a much higher power rating by the manufacturer because boat builders demand high power to weight ratios in order to maximise the performance of their boats. However this higher power rating does mean a shorter life and pleasure boat engines are very unlikely to last as long as an industrial engine before a major rebuild is required.
This is less true of displacement boats though as power to weight ratios are less critical which means that displacement boat builders can use lightly stressed low power engines which tend to last a lot longer in terms of working hours than the heavily stressed high power engines used in planing boats
 
Loggo said:
Can I therefore believe that my 1,450 hour engine will outlive the hull
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Yes, if it's a high duty rated and properly maintained diesel engine.
No, if it's a supercharged 1075hp Mercury petrol engine - no matter how properly maintained.
Maybe, for anything in between.
 
Deleted User said:
Thats true also of industrial engines in things like construction machines and generators; they also spend most of their working lives at near max power. These engines might last 10,000 hours or more. The key difference between pleasure boat engines and industrial engines (which are often closely related) is that pleasure boat engines are usually offered at a much higher power rating by the manufacturer because boat builders demand high power to weight ratios in order to maximise the performance of their boats. However this higher power rating does mean a shorter life and pleasure boat engines are very unlikely to last as long as an industrial engine before a major rebuild is required.
This is less true of displacement boats though as power to weight ratios are less critical which means that displacement boat builders can use lightly stressed low power engines which tend to last a lot longer in terms of working hours than the heavily stressed high power engines used in planing boats
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And the manufacturer only sells the boat once.. and how long/many hours do most of is keep a boat?
 
Obviously it's not an exact science but i'd put the greatest contributing factor to boat engine life is the boats sporadic use.

Boats can go weeks (or months) on end without use which is not great for a long service life.
 
It's not the hours that knacker them, it's the years and lack of service. Plus most boat engines were not built right in the first place. Volvo would soon be out of business, if they made truck engines like boat engines. But they dont, boat engines are called leisure engine and not really intended to go anywhere. Where they do go, there intended to go quickly, like round Silverstone. So like racing cars they dont last long. The older ones are better as they were never so stressed.
 
Fire99 said:
Obviously it's not an exact science but i'd put the greatest contributing factor to boat engine life is the boats sporadic use.

Boats can go weeks (or months) on end without use which is not great for a long service life.
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Thats a good point. My Volvo 2030 has done 3000 hours, but for most of that time it was doing 50+ hours a week as a charter boat with oil and filter changes every 3 weeks or so. Very few sailboat auxiliaries - or indeed any pleasure boat will do those kind of hours. However it is not unreasonable to get 30 years use out of an engine. The big market for engines now is for boats built in the 70's and 80's where the engines are often no longer economical to maintain - or just past it.
 
Rule of thumb - I call it the "number of bangs" rule (Without any basis in fact, but I'm open to suggestions)

ATBE, an engine probably has a design life - like the nature's heartbeat theory.

That depends on:
Number of cylinders
Number of strokes[0]
Fuel - diesel doubles things[0]
Normal operating revs.
Per cylinder capacity.

So a two-stroke, two-cylinder 250cc motorbike revving to 15,000 rpm has a life expectancy of 1/48th that of 4 cyl 2l diesel at 2,500 rpm, and a big lazy V12 diesel[1] will go on forever.

[0] Excepting diesel two-strokes.
[1] I'm not a car fan, but the idea of 740 ft/lb from a boat/train engine in a car appeals ;->
 
Deleted User said:
Thats true also of industrial engines in things like construction machines and generators; they also spend most of their working lives at near max power. These engines might last 10,000 hours or more. The key difference between pleasure boat engines and industrial engines (which are often closely related) is that pleasure boat engines are usually offered at a much higher power rating by the manufacturer because boat builders demand high power to weight ratios in order to maximise the performance of their boats. However this higher power rating does mean a shorter life ...
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You are quite right and I should have said that myself. It's the fact that the maximum power is a high maximum power which matters.
 
It is an impossible question to answer as there are so many variables, and most of the important points such as duty cycle, load ratings, inertia ramming affects, etc have been covered.

There are many things which can be done to improve engine, and engine related peripherals working life.

Engines need running regularly, and to full working temperature, this circulates the oil and coats the internal working components, in addition it allows the oil to work properly in other ways. Oil collects contamination, absorbs condensation, etc; and all in addition to lubricating the engine, and this allows water to evaporate off, particles of contamination to break down, and for the filters to filter contamination.

In addition it is prudent to start engines and allow them to idle for a couple of minutes before revving, particularly if it is a turbocharged engine as it allows oil to fully circulate properly. Likewise when returning after a run, allow the engines to idle for 5 minutes, this gives the turbo's time to slow down and stop while they have a full oil feed to prevent wear.

Run the engines as much as possible, the water will circulate in sealed cooling systems and help prevent scale from forming, and any sediment to settle in the bottom of the engine block. In addition it centralises components such as oil seals, and prevents flat spots on them where shafts have sat in the same position for months.

Giving them a run also lubricates the transmission/sterngear.

Service all engines regularly, or more frequently than recommended, oil and filters are cheaper than major repairs, and cheap insurance.

When it is run, warm the engine fully, open the taps and let it really rip, this will clean the exhausts and get the diesel engine hot, it only needs a short burst of about 5 minutes to clear all manner of soot and debris.
 
Having maintained aircraft that spend a lot of their time near saltwater as well as those that spend comparatively less I think the environment is a huge factor as well as use. Even the Jaguars at Lossiemouth showed noticeably more corrosion than those at Brüggen. The Nimrods at Kinloss had real problems with saltwater corrosion - they even got a washdown at the end of every flight (if the thing was working).

Admittedly that was the airframe but engines in freshwater boats do seem fair a lot better than in saltwater. If you want to see what a near total lack of damp and salt can do go look at the state of some of the 40 year old airframes in the US desert "graveyards"
 
Loggo said:
These days we expect our cars to cover well in excess of 150,000 + miles in a lifetime.
How does this translate into boat engine hours ? I see a lot of boats around 10-15 years old with engine hours of 1000-1500.
Assume a car averages 40 MPH then 1500 hours would be 60,000 miles - around 30% of it's life.
Can I therefore believe that my 1,450 hour engine will outlive the hull :)
or I am I fooling myself ? :rolleyes:

Does anyone have any thoughts on this - how many hours can we expect an engine to last ??
Click to expand...

I have written about this on a number of occasions, however requires some understanding of basic definitions as they are often confused:

Durability. Simply life of engine before blow by and other measurements dictate a rebuild.

Reliability. Generally but not in all cases mission disabiling failure of hang on components. The cause can be poor design or manufacture, or the most common simply 'marine aging'.

To keep life simple I assume OP is referring to engine durability.

All engines wear in relation to the power they are asked to develop, power equals fuel burned. This is the key parameter that is used to estimate engine durability.

As a rule of thumb a typical modern mid range diesel putting out 60 HP per liter maximum and is between 5 and 7 liters total displacement will burn around 25,000 gallons of fuel before the measurements to do with blow-by, oil consumption, compression, etc., would dictate a rebuild. CAT used to publish a durability figure for the 3208 of 25,000 gallons regardless of rating or duty cycle. Forget the engine displacement, it fits into this node, therefore it becomes logical that the 320 Hp rating has higher durability factor expressed in hours than the 425 Hp rating.

Heavy duty engines between 8 and 12 liters putting out around 40 HP per liter are at least 2 but more often over 3 times that. I would expect 65,000-85,000 gallons of fuel consumption on a marine engine in commercial service where the cruise HP is limited to about 30 HP per liter. California is a big re-power market, has large but fast declining population of Detroit motors for which you receive grant funding to replace. As a result there is plenty of documentation of commercial rated 8.3 litre Cummins 350C marine engines burning at least 80,000 gallons long before blow by limit is reached.

You will find many a stories of 3-5 liter G drive engines with 20,000+ hrs and are still running strong..Guess what, the generator engine is averaging .62 to1.25 gph therefore the logic still applies.

Of course, all these estimates of total fuel burn mean nothing if the engine has been running above its designed propeller/ load curve or ??? There are so many things in a boat that affect "practical" engine durability which is why I included 'reliability' at the beginning, and being realistic, the total amount of fuel that an engine has consumed rarely is the factor that causes the engine to be replaced or rebuilt in a recreational application.

Where leasure engine use is typically between 100 and 500 Hrs per year 'marine aging' and operation outside their design envelope kills engines off long before we have burned off our £160,000 worth!!!!!.
 
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Very informative as usual latestarter1. I must admit that I'd never thought of engine life in terms of total fuel burn but it makes absolute sense. What about number of cold starts? Does this have a significant effect on engine life? I was told in the past that engine life was a function of working hours and number of cold starts but maybe this is not entirely correct
 
Personally I think a great deal of marine engine stuff is money for old rope. I know what a certain big car manufacturer does to turn its automotive engines into marine ones and the basics are to strip most of the expensive stuff off and then mark the price up by an eye-watering percentage.

I'm no engine scientist but after owning boats for a decade or so, i'm not surprised why a lot of decent marine engines fail. Often great big diesel engines, treated like little generators with many owners being happier to throw a bucket of money at a 'marine engineer' rather than perform basic maintenance and care of the engine.
 
Loggo said:
These days we expect our cars to cover well in excess of 150,000 + miles in a lifetime.
How does this translate into boat engine hours ? I see a lot of boats around 10-15 years old with engine hours of 1000-1500.
Assume a car averages 40 MPH then 1500 hours would be 60,000 miles - around 30% of it's life.
Can I therefore believe that my 1,450 hour engine will outlive the hull :)
or I am I fooling myself ? :rolleyes:

Does anyone have any thoughts on this - how many hours can we expect an engine to last ??
Click to expand...

I think when comparing cars and boats the only thing that is true is that you cannot compare cars with boats.

Be it engine life, brands, prices, dealers, customer service, recalls, nothing is comparable, you just have to learn the hard way :)
 
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