Hours vs. Distance (miles)

[brad9798]

I just had a conversation with a fellow that was telling me that 1,000 engine hours was the wear/tear equivelant to 10,000 'driving' miles ...

I disagreed, just on gut feel ... perhaps more like 50 or 100,000 miles, I said.

Does anyone 'know' this? Is there a formula?

Now, I just checked on my car trip computer-

Average speed of 28 mph for the last 13 hours of driving time- Or, 364 miles of driving in 13 hours ...

Now, translating that to 'boat math' that would be 13 run hours equals 364 miles--OR--

130 hours = 3,640

1,300 hours = 36,400

Any other thoughts ...

Thanks,

Brad

[Figment]

Boat engines tend to be coddled and maintained FAR better than car engines.
But boat engines spend a lot more time at wide-open throttle.
But car engines probably have a lot more "startup" wear and tear.
but boat engines live in a more corrosive environment (depends on location)....

GAH! Way too many variables... brain overheating...

I suppose a fairly even handed approach to the evaluation would be to compare the average lifespan of the two applications.

Take a smallblock V8 chevy engine for example: In automotive applications, most of these need a rebuild after 150k miles.
In marine applications, I don't know of any that have lasted longer than 2000hours.

This "data" (using the term rather loosely, I think) yields the relationship of 75 miles equals one engine hour. By this evaluation, your gut instincts were correct, but I'll be interested to read about other approaches to the question.

[Nicholas Carey]

Originally posted by brad9798:
I just had a conversation with a fellow that was telling me that 1,000 engine hours was the wear/tear equivelant to 10,000 'driving' miles ...

I disagreed, just on gut feel ... perhaps more like 50 or 100,000 miles, I said.It depends.

Mileage is a lousy metric for scheduling maintenance as there are too many other variables.

You're supposed to change your oil, oh, every 3000 miles, right?

That standard doesn't look at usage. 3000 miles running on the freeway at 70mph is about 43 hours of about the easiest usage on a car engine: non-stop, throttle open, running under a relatively constant load, engine hot.

Look at city driving: 3000 miles there is about 120 hours at 25mph of about the hardest usage possible: stop-and-go, lots of short trips so the engine is often cold, lots of idling at stop, etc.

On top of that, if it's a vehicle like a police car or a taxi, the vehicle spends a lot of its service life at idle: possibly the worst usage possible for an gasoline engine.

Most of the wear on an engine occurs in the first 30 seconds of operation when the engine is cold and galleries aren't yet filled with oil and up to pressure.

A better metric for cars would be operating hours, but that means manufacturers might have to increase there costs by a few buck to install an hourmeter.

Assuming the 3000 mile oil-change interval is designed for "average" use, that works out to changing the oil every 100 or so hours of operation, which would be maybe 75000 miles of freeway driving.

Offhand, I'd agree with you: 1000 hours of boat motor operation is more like maybe 75,000 miles of "driving", but…

It all depends on the use.

Does the boat motor usage consist of 15 minutes of operation each way moving the boat in and out of the marina/slip, or does it consist of motoring from San Francisco to Honolulu. The first case is going to be death on the motor in a hurry unless you shorten the maintanence interval considerable.

[NormMessinger]

If there is any way of comparing I'd think the number of revolutions an engine makes in a mile would be the way. Prairie Islander makes 5 knots at 2300 RPM's and the Ford does about 75 MPH at 2800 rpm in over drive if it is not pulling the boat nor goint up the gang plank in Wyoming. Too much math for me but theres a start, discounting that one is a diesel made in Japan and the other is gas powered made on the west edge of St. Louis.

[ken mcclure]

He might be right.

Automotive driving is done, on the average, at around 30 miles per hour.

Boating is done at far less than that - say around 5 miles per hour.

In that instance, 1,000 boating hours would be the equivalent of 6,000 driving miles.

As said above, though, you also need to consider the amount of actual work the engine was doing. Average rpm is a good way to measure that. So 1,000 boating hours at higher rpm's could well equal or exceed 10,000 driving miles.

[igatenby]

Are we talking gas or diesel? Huge difference between the two.

Í recall reading somewhere that if a diesel is operated flat out, its life drops dramatically.

I rebuilt my two 4-53 Detroit diesels in 2001. Their last rebuild appears to have been in 1968 (there was a builders plate on one engine). They are very low series engine numbers - and I'm told they are from the early 50's. One hour meter had 6,900 on it and the other around 1900 - but who would know what is right?

The 4-53 engine came out in many different guises - including turbo and various states of tune with different injectors. These things are simple to rebuild - new sleeves, bearings and away you go. Not many similar options with most car engines. The maximum revs for any 4-3 was 2,800 - a lot less stressed than any car - and probably not operated in a boat at over about 2200 continuous.

Again - its how these things are used that is important - how often the oil is changed - whether the right oil is used - how often the engine is used, etc.

Ian

[Ross M]

Let’s take a look from a Horsepower Hours perspective.

Assume the auto engine in question delivers 17.5 miles per gallon for 175,000 miles
Fuel consumption = 175,000 miles / 17.5 miles per gallon = 10,000 gallons of fuel
10,000 gallons x 6.1 pounds per gallon = 61,000 pounds of fuel

We know that specific fuel consumption is probably a little worse than .6 pounds per horsepower hour, but for the sake of simple math lets use .61:
61,000 pounds / .61 pounds per horsepower hour = 100,000 horsepower hours

Just for fun, let’s look at the engine life and average horsepower in the previous example:
175,000 miles / say 50 miles per hour = 3500 hours
100,000 horsepower hours / 3500 hours = 28.57 horsepower

Now let’s say we are running this engine in a boat at 100 hp (burning 61 lbs – or 10 gallons - per hour)

Life = 100,000 horsepower hours / 100 horsepower = 1000 hours

This sounds about right to me: 1000 hours at 100 horsepower, 500hrs at 200 hp, 250 hrs at 400 hp.

1/3.5 , 1/7th and 1/14th of auto duty life, in hours, respectively.

This all probably reduces better in pounds per hour, but I’m not gonna do it tonight…

Ross

[ahp]

Revolutions and revolutions/minute are a better indecator of wear than hours or horsepower hours. Another good indecator is piston travel per mile of autos, and piston travel per hour for boats.

By the way, I once measure much power was required to keep my Merc Sable station wagon rolling at 60 mph - 25 hp.

[Figment]

I think that the fuel consumption approach is probably the most accurate. After all, there is a reasonably direct relationship between energy consumed and work produced, right? I think it stands to reason that there is also a direct relationship between work produced and wear imparted.

Too bad this is completely usless unless you can find an automobile and a boat using the same engine that both have the ability to accurately track fuel consumption.

[Paul Pless]

apples and oranges . . . . .

[Del Lansing]

This thread made me think about aircraft engines. Since they are operated more similarly to watercraft engines than wc engines to automobile engines. Why not use the oil filter analysis program for WC engines? They analyse the metal particles trapped in the filter and can give a report on rod bearing wear, cam wear, cylinder wear. This can pinpoint premature failures and indicate fairly accurately when it's time to rebuild. Just wondering.

[phiil]

Back when I was the token male at a feminist service station, I did some work on an old Land Rover. The service manual for the vehicle specified oil changes, et cetera, not after a certain mileage interval, nor hours, but per gallons of fuel consumed. Makes sense to me. If you change your oil after every, say, 200 gallons of gas used, it might be 6000 miles of easy highway driving, 3000 miles of city driving, or a week of using your hummer to drag teak logs out of the rain forest to build your boat.

[imported_Conrad]

"Gallons of fuel consumed" is the standard measure for commercial diesel installations and their maintenance scheduling, so Ross wins. ;) And his math bears him out, as the 125-150,000mi/1500-2000hrs comparison suggested elsewhere is also widely accepted.