Engine hours when buying a used trawler

[STB]

I'd totally ignore whatever the Hobbs/Hours gauges read. Unless they are accompanied by detailed trip logs and maintenance logs, there is little reason to believe they are correct.

My present boat has two engines and a genset. The hours read correctly on none of of above. One engine was rebuilt before the gauge was replaced, another engine was replaced after the gauge was replaced, and the genset controller that contains the hours time was replaced, resetting the hours to zero.

In my case, my operations logs detail hours of use and measures hours, as well as the gauge offsets. And my maintenance log details when everything was replaced and the hours. I've also snickered each gauge and the genset controller indicating the offset to get actual hours from the gauge/display hours. But my level of detail in documenting that is somewhat rare, I think, as is one owner having been around since all three engines were very new to keep the history well documented.

I'd focus on what you can tell with your own senses, i.e. smoke color, temperature, time to start, rust/corrosion, apparent age ofaontenance items and -- receipts.

Enjoy the boat!

 

[OldDan1943]

It has been said, a lightly loaded diesel generator will not last as long.
I am not saying your main engine should be run WOT 24hrs a day although I did run my JD, naturally aspirated, WOT for 2 or 3 day with no ill effects. Yes, it was well broken in by the time I got the N46.

 

[mvweebles]

While I don't disagree with the legions of "If it's been well maintained it will go 20,000 hrs....." responses, I'd personally start taking a hard look at the engine, drive train (including transmission) and shaft at around 4000-5000 hours with an eye towards a credit for high hours. Unlike commercial vessels that may put 2500 hours a year on their diesel, recreational vessels rarely put more than 200. Shafts, couplings, seals, impellers, coolers, turbos, gaskets, etc all break down with age. You may not need a total overhaul or rebuild, but leaking main seal, head gasket, valves, injection pump, injectors, and other components are wear items that have decent chance of material failure within 5000-6000 hours. The internal engine itself may last 15k-20k hours, but the stuff that's bolted on to it won't.

Good luck

Peter

 

[High Wire]

The engine could have been treated perfectly and you could still have a failure tomorrow. You do your due diligence on the purchase and follow the manual for operation and maintenance. Don’t buy a boat with a one-of-a-kind engine or is a chunk of rusty iron unless you plan to repower from the git-go.

 

[backinblue]

Here is the response I just received from Yanmar regarding my engine.

Here is the spec sheet on the 6LP Engine.
If you look at the torque chart the engine plateaus at 2400-3000 Rpms.
the best fuel consumption is between 2400-3000 rpms.
The engine normally jumps and goes at 2800 rpms that when you here the turbo spool up.
I would say that some where between 2800-3100 is where I would be running it for max torque and fuel economy
You would need to check speeds at different Rpms on the engine to see which would give you max speed at those Rpm ranges.

 

[firehoser75]

That is interesting backinblue.
For my Cummins 6BTA, the torque curve starts to flatten above 1700 rpm. However, for my Tug the best fuel consumption (based on miles travelled per gallon burned) is about 1200 rpm. At 1200 rpm the boat usually achieves 7 knots burning 2.0 gallons per hour giving 3.5 miles per gallon. At 1400 rpm the boat goes about 7.5 - 8 knots (hull speed -) and burns 2.8 gallons per hour giving 2.85 miles per gallon. At 1600 rpm the boat goes about 9.5 knots, pushes a lot of water barely on plane and burns 8.5 gallons per hour giving 1.12 miles per gallon. This means for an NT 37 with a 370 hp 6BTA that to achieve approx. 10- knots you use more than double the fuel per mile travelled compared to travelling at 7-8 knots (approx. hull speed). At higher rpm's the fuel consumption does not improve, it gets much worse on a miles covered per gallon of fuel as speed does not increase at the same rate. At WOT the boat goes about 15 knots and burns 16.8 gallons per hour achieving only 0.89 miles per gallon of fuel while making a large wake on plane.
To be clear, that is real world speeds measured as my boat was loaded using "rated fuel consumption for that rpm".
According to Tony Athens, a well respected marine diesel expert (on sbmar.com), he has never seen a marine diesel engine "fail" due to being run under load at 1/2 throttle (in other words low rpm operation being the cause of failure). I am paraphrasing, but that is the gist. For a turbo charged engine like the Cummins 6BTA, he does recommend periodically running at 80% to WOT for 5-10 minutes to "heat it up" to burn off any carbon, and to check for any signs of developing issues (like higher than normal temps, leaks, etc.). At those rpm (12-1400) the engine does reach a proper operating temperature of 180-185 degrees. He does not say the engine cannot be safely operated at 80% throttle as cruising speed. However, the operating error is less and the engine needs to be in good condition and not overloaded or over propped.
Back to engine wear and looking at it logically and theoretically:
An engine run at 2200 rpm (80% for the 6BTA) in 10,000 hours that is 1,320,000,000 revolutions.
For the same engine run at 1400 rpm in 10,000 hours that is 840,000,000 revolutions. That works out to only 64% of the revolutions. All other things being equal that has to mean "less overall" internal wear as motion is what causes wear???
In the real world, there are many other factors that enter into the engine life discussion but the logic should apply.

 

[backinblue]

That is interesting backinblue.
For my Cummins 6BTA, the torque curve starts to flatten above 1700 rpm. However, for my Tug the best fuel consumption (based on miles travelled per gallon burned) is about 1200 rpm. At 1200 rpm the boat usually achieves 7 knots burning 2.0 gallons per hour giving 3.5 miles per gallon. At 1400 rpm the boat goes about 7.5 - 8 knots (hull speed -) and burns 2.8 gallons per hour giving 2.85 miles per gallon. At 1600 rpm the boat goes about 9.5 knots, pushes a lot of water barely on plane and burns 8.5 gallons per hour giving 1.12 miles per gallon. This means for an NT 37 with a 370 hp 6BTA that to achieve approx. 10- knots you use more than double the fuel per mile travelled compared to travelling at 7-8 knots (approx. hull speed). At higher rpm's the fuel consumption does not improve, it gets much worse on a miles covered per gallon of fuel as speed does not increase at the same rate. At WOT the boat goes about 15 knots and burns 16.8 gallons per hour achieving only 0.89 miles per gallon of fuel while making a large wake on plane.
To be clear, that is real world speeds measured as my boat was loaded using "rated fuel consumption for that rpm".
According to Tony Athens, a well respected marine diesel expert (on sbmar.com), he has never seen a marine diesel engine "fail" due to being run under load at 1/2 throttle (in other words low rpm operation being the cause of failure). I am paraphrasing, but that is the gist. For a turbo charged engine like the Cummins 6BTA, he does recommend periodically running at 80% to WOT for 5-10 minutes to "heat it up" to burn off any carbon, and to check for any signs of developing issues (like higher than normal temps, leaks, etc.). At those rpm (12-1400) the engine does reach a proper operating temperature of 180-185 degrees. He does not say the engine cannot be safely operated at 80% throttle as cruising speed. However, the operating error is less and the engine needs to be in good condition and not overloaded or over propped.
Back to engine wear and looking at it logically and theoretically:
An engine run at 2200 rpm (80% for the 6BTA) in 10,000 hours that is 1,320,000,000 revolutions.
For the same engine run at 1400 rpm in 10,000 hours that is 840,000,000 revolutions. That works out to only 64% of the revolutions. All other things being equal that has to mean "less overall" internal wear as motion is what causes wear???
In the real world, there are many other factors that enter into the engine life discussion but the logic should apply.

Thanks Tom for the thorough reply. I have a couple comments.

My boat likely gets up on plane much easier than yours. So unless I am purposely taking it slow to save fuel or because I'm in no hurry to get anywhere, I am usually on plane. So in that case, as recommended, I might as well run it up to about 3K RPM for better speed as well as efficiency. My Engine manual specifically states that it is safe to run at 80% of max for 90% of the time.

Regarding wear and tear, I agree that higher RPMs means more engine revolutions and therefore more wear. But it also means more distance traveled. So if you know you are going out for a 4-hour cruise, lower RPMs is better. However, if you know you have 50 miles to travel, I'd suggest that prop revolutions (i.e. engine revolutions) would be close to the same for a given distance. Lower RPM's just means you have to run longer to cover the same distance and as a result also increasing the hours on your engine meter.

BTW, just because 3K RPM is my most efficient speed on plane, my max mpg would still be at or below hull speed. It reportedly gets about 4 mpg at 7 knots, but I've never verified it. All good stuff to think about, thanks.

 

[firehoser75]

I agree completely with you thoughts. Different boats, different operator desires (including different ways of enjoying the boating experience), mean there is more than one way to operate a lot of these boats, especially semi-displacement hulls with higher HP engines.
But back to the OP and his question. This discussion/thread has highlighted that engine hours alone only give SOME of the story when looking at an older boat. Probably way more important is maintenance, loading, and how the boat was operated.
Good discussions though.

 

[FF]

Before electric meters were measuring hours of operation many tachs were mechanical and includes total engine revolutions .

Don't know how the engine life was figured , but the tachs seldom wore out , unlike the electric hour meters, so might have been more honest.

 

[Hippocampus]

Believe a lot of wear and tear occurs at start up and there’s some also when turned off. Commercial and passage making boats get turned on and left on for days. That’s a very different experience for the engine(s). Been taught to let things warm up before leaving and run near WOT briefly then idle with no load until temps drop a bit before turning off. Especially for turbocharged engines. Been told dry stack set ups are a bit less likely to be injured by operator errors or negligence. (Don’t know the truth of that). Been told many recreational boats are way over powered and that situation has a negative impact on longevity (again don’t know the truth of that). However, have heard variations of these statements from multiple wrenches and when doing diesel courses.
Lament the tiers. Continue to believe a naturally aspirated, mechanically controlled engine with a bulletproof cooling system may be less efficient and more polluting but for a yahoo like me a safer bet for a trouble free long life.

 

[mvweebles]

This topic always irks me. It's a question I asked when I was a newbie so I fully understand the reasoning behind it. But now that I have some miles beneath my keel, I realize 99% of the answers are passed-along, not actual experience. Very few people put more than about 200 hours per year on an engine, so there's no way they get to 15k hours unless they are a commercial operator, which is a much different use-case.

I probably know of 20 or so engines that were either re-powered or overhauled. Only one was due to wearing out: a 1960's era Pacemaker 65 with DDs that I drove as a dinner-cruise boat on SF Bay (>15k hours at time of overhaul, and it was still running fairly well, but was overhauled during a slow period). The other 95% of the engines were overhauled due to something breaking or deferred maintenance. I once had a raw water pump shaft break and caused a Cummins 555 to overheat which caused around $8k in repairs.

So I view this topic with a huge amount of skepticism. Saying that a decent diesel engine will go xx-thousand hours or some variant ("5000 hours is just barely broken-in!!!") is misleading. First, of the 1000s of people who own a trawler, I know of only a couple people who have put 5000+ hours on a recreational trawler - around 30,000 miles. Just doesn't happen very often, so saying an engine can girdle the globe 4x (20k hours) isn't realistic. Second, I still maintain that at around 5000 hours (or 20-years), the engine is getting tired not so much from the internals, but all the other stuff. It may not need new pistons/liners/journal bearings/etc, but if it hasn't had a full R&R of the bolt-on stuff like pumps, coolers, injectors/pump, valve-cover/oil-pan gaskets, hoses, etc. it needs it soon. That can easily be $10k in maintenance (I know, everyone caveats their answer "can easily go 15,000 hours as long as its well maintained." I'm here to say that there's ongoing maintenance and periodic major maintenance, the latter is damn expensive). And we haven't even begun to talk about the transmission which is doubtful to last 20k hours (or even 10k hours).

I'm sorry, I simply cannot in good faith suggest to a prospective buyer that they shouldn't worry about an engine with 5000+ hours on it. In my mind, the right answer is 5000 hours (whatever the number is) isn't necessarily a deal killer, but it's a strong yellow flag and a prospective buyer should plan for additional due diligence.

Okay, I feel better to have gotten that off my chest. I'll stand-down now....thanks for bearing with my rant

Peter