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Old 03-03-2015, 02:49   #1
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Engine cost per hr of operation

It seems to me in one of Nigel Calder books he had explained the actual cost per hr of running your engine. I know it varies with size, but I have a 65 hp Perkins and I would like to know what it cost to run it on a per hr bases.
Does anyone have that information from his book or know what it works out to be?
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Old 03-03-2015, 03:48   #2
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Re: Engine cost per hr of operation

Probably a lot more than we'd like. I bounced some numbers around for our 96hp a year ago. I'll be interested to see what people come up with but on our engine, from memory it was Au$7 per hour for fuel, au$1 per hour for oil (we do short engine runs so our oil gets little milage, working on two oil changes a year at $50 each for 100 hours annual use) and I assumed a significant rebuild at 5000 hours so another au$2 per hour there, plus around half that for the trans rebuild at the same time so another au$1 per hour. Finally belts and filters every year which means another au$1 per hour.

Rebuild figures are based on me doing the work, most of which is within my skill set, though injectors etc would be outsourced.

I figure shaft seal is going to last five years with or without use so I ignored that item. Ditto the various couplings, engine mounts all of which appear to age with or without use. Maybe the cutless is affected by use more than age. Not sure about that one.

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Old 03-03-2015, 04:11   #3
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Re: Engine cost per hr of operation

A flat per hour price is useless without knowing how you use the engine.

Our last boat had 30yr old engines that were still running fine when we sold it. Someone who abuses an engine might not get 5yrs out of an engine. The cost per hour will be drastically different for the two cases.
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Old 03-03-2015, 04:47   #4
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Re: Engine cost per hr of operation

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Originally Posted by valhalla360 View Post
A flat per hour price is useless without knowing how you use the engine.

Our last boat had 30yr old engines that were still running fine when we sold it. Someone who abuses an engine might not get 5yrs out of an engine. The cost per hour will be drastically different for the two cases.
how do you not abuse engine ?
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Old 03-03-2015, 04:54   #5
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Engine cost per hr of operation

Don't run it for short amounts of time under light load (e.g. Power generation and leaving slips), change the oil religiously, and be very careful to give it clean fuel and air.


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Old 03-03-2015, 04:58   #6
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Re: Engine cost per hr of operation

It's figured all the time for aircraft, and GIlow pretty much nailed the formula.
One way is to figure 25K for an engine, 10,000 hour life = $2.5 per hour, add fuel and maintenance costs.
You determine engine cost and average life, but you get the idea
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Old 03-03-2015, 05:00   #7
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Re: Engine cost per hr of operation

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Originally Posted by arsenelupiga View Post
how do you not abuse engine ?
Lots of ways:
- A leaky shaft seal spraying salt water on the engine.
- Running the engine with low oil because you don't check it.
- Running the engine for long periods at full throttle
- Not changing belts and then they break while the engine is running.
- Overheating due to leaks that could be avoided with maintenance replacement of hoses.
- Sitting for long periods so seals and gaskets dry out.
- Etc....

From what I've seen, most boat engines die an early death due to abuse and neglect not because they are worn out from a long life.


a64pilot: It may be figured all the time but does it have any relationship to reality? Then again aircraft have strict govt regulations to follow that boats do not.
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Old 03-03-2015, 05:12   #8
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Re: Engine cost per hr of operation

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Originally Posted by a64pilot View Post
It's figured all the time for aircraft, and GIlow pretty much nailed the formula.
One way is to figure 25K for an engine, 10,000 hour life = $2.5 per hour, add fuel and maintenance costs.
You determine engine cost and average life, but you get the idea
I have always been fascinated by this aspect of aircraft maintenance, and as my son becomes more and more involved in flying these numbers are starting to prey on my mind a bit.

I figured 5000 hours for a boat diesel, is your 10,000 hours above for a boat diesel or an aircraft engine? In other words, do you think I am being pessimistic assuming 5000 hours?

Finally, Valhalla360, fair point you made about not abusing the engine, but surely we could work the OP's question on the basis of sound maintenance, with a caveat that should you neglect and engine then the sky is the limit when it comes to hourly running cost?

Having watched a friend blow up their engine last year because of simply failing to deal with poor coolant flow when it was apparent there was a problem, I concede that cost is very much inversely proportional to diligence.


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Old 03-03-2015, 08:47   #9
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Re: Engine cost per hr of operation

Are newer engines less resistant to overheating? I believe they are built to finer tolerances so they may be. And there seem to be a lot of stories here about wrecked engines from overheating.
The 1980 universal in my boat became so hot it seized and shut off (before my ownership), but on my third day of ownership (due to a lack of an overheat alarm and me being up at the mast), it got to 210 before I realized the water passage was blocked. Seems to motor fine now, actually think it was good for it to blow out some of the buildup. Less white smoke from cool running coming from it now. Overheating the engine is how a lot of insight owners clean out their egr valves too.


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Old 03-03-2015, 09:04   #10
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Re: Engine cost per hr of operation

For a commercial operator running cost per hour is an important concept. Probably also applies to anyone putting significant hours on their engine(s).

We only accumulate 50 to 150 hrs per year. We do oil and coolant changes far more often than if the engine was used everyday. So a cost per hour would be relatively high. We are more focussed on our strict preventative maintenance regime. Its always a balance between reliability, availability and maintainability. Too much maintenance reduces availability and vice versa.

Its always a tradeoff between preventative and corrective maintenance. I have a motorsport background so wont tolerate sloppy maintenance dirty engine room, poor access or unreliability.

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Old 03-03-2015, 09:09   #11
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Re: Engine cost per hr of operation

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Originally Posted by brownoarsman View Post
Are newer engines less resistant to overheating? I believe they are built to finer tolerances so they may be. And there seem to be a lot of stories here about wrecked engines from overheating.
The 1980 universal in my boat became so hot it seized and shut off (before my ownership), but on my third day of ownership (due to a lack of an overheat alarm and me being up at the mast), it got to 210 before I realized the water passage was blocked. Seems to motor fine now, actually think it was good for it to blow out some of the buildup. Less white smoke from cool running coming from it now. Overheating the engine is how a lot of insight owners clean out their egr valves too.


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Its a bit like asking how long is a piece of string.

Any engine has an ideal tolerance for all mating parts. This is so that when at operating temperature an oil film can form between mating parts sufficient to carry the imposed loads and avoid metal to metal contact. Modern engines are optimised for low cost, light weight and emissions. The use of lightweight materials also introduces greater thermal expansion variance between components. This usually dictates tighter tolerances. Its all about oil hydrodynamics and thermal loading for all engines.

Engine cooling is not black magic. The laws of thermodynamics apply always. On a more practical level. Heat moves from the engine to the cooling system and then heat is dissipated to the atmosphere or heat sink (raw water in our case)

The particular installation matters. I measured temps all over the engine and generator cooling systems when we were new to our boat. This allowed me to identify any specific issues, understand normal running and calibrate all gauges. A handheld infra red gun makes this take trivial these days.

We have also added temp lights for all cooling including all water and oil. Gauges are fine but an idiot light is a simple reliable backup to protect an expensive engine system. A big light or a screecher is cheap insurance.

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Old 03-03-2015, 09:23   #12
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Re: Engine cost per hr of operation

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Originally Posted by brownoarsman View Post
Don't run it for short amounts of time under light load (e.g. Power generation and leaving slips), change the oil religiously, and be very careful to give it clean fuel and air.


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What do you do when leaving slip using engines ? After 5 min engine not needed any more. My yanmar manual says to give it 5 bursts of high revs and then turn off.

Have I got this right ?
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Old 03-03-2015, 09:46   #13
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Re: Engine cost per hr of operation

the cost of siting in a seawater enviroment is probably greater that the cost of running hours.
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Old 03-03-2015, 09:48   #14
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Re: Engine cost per hr of operation

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Originally Posted by arsenelupiga View Post
What do you do when leaving slip using engines ? After 5 min engine not needed any more. My yanmar manual says to give it 5 bursts of high revs and then turn off.

Have I got this right ?
Five 2 minute bursts with no space between and it's probably fine. The problem is if you only run the engine for 5 min at low speed and turn it off, you aren't getting it up to temperature. Five quick bursts of 3-4 seconds, isn't going to get it up to temperature.

There probably is some benefit to what the manual says but that's likely a better than nothing suggestion. 10-15minutes under load is what I've always been told.

Of course, if that's the extent of your motoring, I'd be suprised if you put more than a couple hours a year on the engine, so if you to a preventative oil and filter change, you are probably up around $30-40/hr.
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Old 03-03-2015, 10:04   #15
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Re: Engine cost per hr of operation

Thanks for the detailed response left brain. I was thinking about getting an infrared thermometer, and it looks like now I will! I have great engine access so it should be okay, and I'll definitely add an overheat alarm.


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