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Old 06-22-2017, 08:13 PM   #1
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Engine hours....

You are offered a choice between 2 identical boats, one has 1,500 hours and the other 3,000 hours. Both maintained to the highest standards and priced about the same. The choice is obvious, but wait you just found out the higher hours boat routinely cruised at 8 knots, while the lower hours boat cruised at 17 knots. Would this alter your decision?
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Old 06-22-2017, 08:17 PM   #2
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Engine make? Gas or diesel? Single screw or twin? Boat make and model? Not enough info for an opinion.
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Old 06-22-2017, 08:23 PM   #3
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Greetings,
Mr. New. All depends on what engine we're talking about. Is the engine designed to go 17 knots continuously? Meaning is this in a boat that will do say, 22 knots flat out or is it a boat that will do 17 knot boat flat out? IF it's in a 17 knot boat, I'd take the one run at lower RPM. Not good to run pedal to the metal for any length of time unless designed as such IMO.
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Old 06-22-2017, 08:30 PM   #4
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Ok so to add to my hypothetical an engine that can do 22 knots WOT but designed to cruise continuously between 8 and 17 knots.
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Old 06-22-2017, 08:54 PM   #5
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OK, now you are talking about engine duty cycles and ratings. For that, see Steve D'Antonio's article on rating.

My engine is rated M1 which is BTTW, or WOT, 24 hours a day. 250 hp, 2100 rpm. That's different than an identical engine with a different turbo and injection pump (camshaft?) called a Diamond Series which might be rated 1 hr BTTW out of 24, but he gets 475 HP at about 2600 rpm (I don't remember the exact numbers).

So, running my motor flat out for 3000 hours vs the Diamond at the same? Depends if the owner respected the manual...

We need to know the engine and the boat for a better answer.

In simple terms, 3000 hours is nothing if its been well maintained.
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Old 06-22-2017, 09:44 PM   #6
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...2 identical boats...
I don't think so.
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Old 06-22-2017, 11:42 PM   #7
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Some hour meters count the minutes an engine runs and some have a factor that adds hours based on rpm.
My experience is in heavy duty engines not smaller yacht diesels. In my time I have personally overhauled or watched the overhaul of many engines that I knew the hours and operating conditions of the engines. Engines run near wot do not last as long as engines kept under 80% of max hp. In some engine makes that can mean twice or triple the span between overhauls. Turbo engines almost always have a short span compared to their non turbo models. Continuous wot can cause damage beyond normal wear. Sometimes in sleeved engines the waterjacket becomes distorted and has to be rebored requiring special sleeves. Why larger sport fishing boats often have very expensive overhaul. Going 25 kts instead of 30 saves more than fuel. Excessive heat also leads to cracks. Just because the coolant doesn't overheat isn't a sign of safe operation. At high hp, cavitation (small bubbles form on the water side of the waterjacket) causes deep pits that are not fixable.
Engine makers want to sell engines and adjust their max and continuous rpm on the market. Commercial engines have to last or no more engines would be sold. But yacht engines are used lightly and I believe the continuous rpm specs are given planning on the engines to be off warranty when they fail.
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Old 06-23-2017, 12:33 AM   #8
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Rule o' thumb I go by:

HP number should be no more that 85% compared to cubic inch displacement... lesser %age is even better.

Engine should not be continuously run above 75% total output... 70% is even better... occasionally higher throttle for short duration is OK.
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Old 06-23-2017, 05:12 AM   #9
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"Both maintained to the highest standards"

Describe what each owner considered the "highest standards".
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Old 06-23-2017, 06:28 AM   #10
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This is an impossible thread without more info from the OP.
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Old 06-23-2017, 06:46 AM   #11
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This is an impossible thread without more info from the OP.
Donna - Please!!! It hurts me to see you bang your head against the wall!

or would not hurt so much!!
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Old 06-23-2017, 06:50 AM   #12
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Donna - Please!!! It hurts me to see you bang your head against the wall!

or would not hurt so much!!
Too funny Art! Maybe I'll just get some
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Old 06-23-2017, 07:23 AM   #13
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Too funny Art! Maybe I'll just get some
With butter??
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Old 06-23-2017, 07:46 AM   #14
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Let me rephrase the question. I don't want anyone to split their heads open. You are offered a choice of 2 diesel engines for free (not a choice of boats although the engines came from the exact same boat with single engine and with exact same transmissions). They are identical make and year manufactured. They are maintained equally. Per manufacturer guidelines the boat can do 23 WOT. They can cruise continuously between 8 and 17 (75% of 23 max). One owner cruised at 8 knots and the motor has 3000 hours, the other cruised at 17 and the motor has 1500 hours. Which motor do you pick. If you need a brand lets say Yanmar. That's the only info you have, which one do you take and why. Everyday we are forced to make decisions with the facts we have. This may not be a perfect question but I think most would understand the jest of it. Please be patient with me, as I am a newbie.
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Old 06-23-2017, 08:00 AM   #15
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Let me rephrase the question. I don't want anyone to split their heads open. You are offered a choice of 2 diesel engines for free (not a choice of boats although the engines came from the exact same boat with single engine and with exact same transmissions). They are identical make and year manufactured. They are maintained equally. Per manufacturer guidelines the boat can do 23 WOT. They can cruise continuously between 8 and 17 (75% of 23 max). One owner cruised at 8 knots and the motor has 3000 hours, the other cruised at 17 and the motor has 1500 hours. Which motor do you pick. If you need a brand lets say Yanmar. That's the only info you have, which one do you take and why. Everyday we are forced to make decisions with the facts we have. This may not be a perfect question but I think most would understand the jest of it. Please be patient with me, as I am a newbie.
I recommend buying both... one to use and one as a spare! - Trying to keep it light here.

You could do same question on a duplicate car. Both with similar [car wise that is] criteria as you mention above.

I'd say get an expert to survey each engine. Then you'll have better stats on condition of each. After all... they are both "used" engines.
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Old 06-23-2017, 08:44 AM   #16
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I believe what NewbieF is driving at, is which powerplant would have the (Less wear and tear!)


I remember a vessel for sale on yachtworld, where the vesselís powerplants (Cats) had something like 3,400 hrs. on them. However the owner only ran the vessel at 8knot max.


The Broker stated in his sales pitch, that based on the fuel consumption data from Caterpillar the hours on the powerplantís would be more like 900hrs and some change.


To me it is a crap shoot as to which powerplant has less wear and tear. You never know when a powerplant will start having issues even when well maintained. Iíve seen powerplants with low hrs. fail and seen powerplants with high hrs. run like champs.


So there for, to me there is no clear cut answer to which powerplant would be better.


Cheers.
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Old 06-23-2017, 09:16 AM   #17
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Quote:
Originally Posted by Lepke View Post
Some hour meters count the minutes an engine runs and some have a factor that adds hours based on rpm.
My experience is in heavy duty engines not smaller yacht diesels. In my time I have personally overhauled or watched the overhaul of many engines that I knew the hours and operating conditions of the engines. Engines run near wot do not last as long as engines kept under 80% of max hp. In some engine makes that can mean twice or triple the span between overhauls. Turbo engines almost always have a short span compared to their non turbo models. Continuous wot can cause damage beyond normal wear. Sometimes in sleeved engines the waterjacket becomes distorted and has to be rebored requiring special sleeves. Why larger sport fishing boats often have very expensive overhaul. Going 25 kts instead of 30 saves more than fuel. Excessive heat also leads to cracks. Just because the coolant doesn't overheat isn't a sign of safe operation. At high hp, cavitation (small bubbles form on the water side of the waterjacket) causes deep pits that are not fixable.
Engine makers want to sell engines and adjust their max and continuous rpm on the market. Commercial engines have to last or no more engines would be sold. But yacht engines are used lightly and I believe the continuous rpm specs are given planning on the engines to be off warranty when they fail.
Don't know what heavy duty engines you are referring to but a large commercial engine without a turbo or four has been nigh impossible to find for a very long time. Certainly not found in a diesel powered 45 footer capable of running 22 knots.

When I first got out of college a half century ago and started working with large fixed and mobile equipment engines they all were with turbos. Quite honestly I never worked around large mobile equipment without turbos. I'm referring to very large equipment where computer controlled injection and boost situations are managing up to a 200 gph fuel burn rate.

Engine life was and is easily warrantied to above 15,000 hours on "balls to the walls" multi thousand HP engine blocks running 24/7. Engine bolt ons such as pumps, alternators and injection systems have a shorter life span.

Whether genset or large mobile equipment applications, the heart and soul of big commercial engine longevity centers on lubrication and heat dissipation. Tracking fuel burn and power output ( continually downloaded) along with oil analysis is a science in itself. It has to be on say a 4 turbo 4000 HP haul truck engine pulling 100% rated load out of a deep open pit at 4700 meters.

So turboed engines having much shorter lifespans? Not in my world, no comparison possible in this era because non turbo heavy duty engines of plus 150 HP or so are nearly impossible to find and aren't legal anyway.

Yeah I know, all sorts of non turbo low HP diesel engines can be purchased for auxiliaries and Gensets. In these cases HP and engine size are not too relevant. But get to the class of marine or industrial engines the OP is referring and turbos are there, in 100% of the cases.
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Old 06-23-2017, 09:17 AM   #18
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I would pick the high-hour, slower-run, boat.

There may be less wear and tear on the boat in general, as well as all of the engine perhiperals, due to the slower speeds. Think about crashing through the seas at the higher speed, and proper warm up and cool down, for example.

PERHAPS the more thoughtful engine operation was in line with an overall slower, more deliberate, person that was more meticulous about correct maintenance...yes a stretch, but we all know some people we would never buy any boat from...and some we know take excellent care of their equipment.



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Old 06-23-2017, 09:30 AM   #19
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Total fuel consumption over the lifetime of the engine will be more telling than total hours, so I would choose the high hour, slow running engine.
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Old 06-23-2017, 09:47 AM   #20
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Absolutly yes it would alter my decision.

I would probably avoid the boat with 1500 HARD hours on it.

My exact boat the Bayliner model 4788 is a prime example of this.

The boat comes equipped with twin Cummins 330 HP engines.
The boat (like many SD boats) is propped by the factory for performance. Load the boat up with thousands of pounds of "owner add ons" and the boat is slightly overpropped. Add in a dirty bottom and the boat is even more overpropped.

At displacement speeds the engines are really not harmed by this overpropping.
At a "fast cruise" of 14-15 knots the Cummins engines (which are HIGHLY sensitive to overpropping) are certainly harmed, and even if they are not harmed they are MUCH further into their useful life than a set of engines that are run at displacement speeds most of the time.

On a SD boat, one of the MOST important things to check pre purchase is how the boat was cruised. This can be determined subtly by questions, or definitively by good log book records showing fuel taken onboard.
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