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Old 03-07-2016, 11:17 AM   #81
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BandB,

Yes I was making a general statement, but was thinking that a 200 hp engine and a 300 hp may be essentially the same size, but the additional turbos give the engine greater oomph (technical term). I guess what I was getting at is a friend has an identical boat to mine, but has twin Cat NA 210 horsepower engines. He claims he will get better fuel economy than turbo charged cummins 6BTA. Everything I have read says it takes same amount of energy to propel boat at same speed.

But, perhaps that is pure physics and doesn't hold true in the real world, because of the other considerations. Because I haven't closed on the boat yet, we survey next week, I won't know for some time.

How many of you use fuel scan to track instantaneous consumption?

Gordon
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Old 03-07-2016, 11:35 AM   #82
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Quote:
Originally Posted by Gordon J View Post
I guess what I was getting at is a friend has an identical boat to mine, but has twin Cat NA 210 horsepower engines. He claims he will get better fuel economy than turbo charged cummins 6BTA. Everything I have read says it takes same amount of energy to propel boat at same speed.
Same amount of energy, but no two engines produce that energy the same. One way do so more efficiently than the other. Plus we're talking engine hp on much of this and hp at the propeller is what is more important. Even then you have alternatives among props to achieve different results. Just so many factors. His claim may well be true at certain speeds. I have no idea. I'd have to see actual data before I'd speculate.
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Old 03-07-2016, 12:30 PM   #83
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BandB wrote on post # 79;
"I have charts in front of me on one boat of two engine choices. The larger hp gets better fuel economy at every low speed than the smaller one. Now these come from the same basic block. However at each speed the lesser hp is turning more rpm to achieve the same speed and is less efficient. Then I'm looking at two planing hulls, two different boats. The smaller but faster boat with the smaller engine is tuned in such a way that it has no slow speed economical level. The other boat doesn't achieve the top end but at slow speeds is far more efficient with the larger engine."

It would seem to me the smaller engine should be more efficient if not the smaller engine w higher rpm. Big cylinders are a heat sink and heat loss is very bad for efficiency. There of course there are many variables and the domino effect could skew one example not in the normal direction.
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Old 03-07-2016, 12:54 PM   #84
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It would seem to me the smaller engine should be more efficient if not the smaller engine w higher rpm. Big cylinders are a heat sink and heat loss is very bad for efficiency. There of course there are many variables and the domino effect could skew one example not in the normal direction.
Well, I've seen examples in all types of boats but let me give you a specific example I have in front of me. I recognize it's not in full displacement boats.

Boat A, 65' Flybridge. 1000 hp MAN's or 1200 hp MAN's. The 1000 hp requires 1200 RPM to achieve 10 knots and does so at 0.6 nmpg. The 1200 hp requires 900 RPM to achieve 10 knots and does so at 0.93 nmpg. In fact, the 1200 hp is more efficient at all speeds, from 9 knots to 28 knots.

Boat B is a 44' open boat from another builder. 800 hp MAN's. At 10 knots it is turning 900 RPM and doing so at 0.8 nmpg. The unique thing about Boat B is that it gets 0.6 nmpg at 40 knots and just has a very gradual curve.

Actually Boat C from the same builder as Boat B has 1360 hp MAN's. It is similar in that it's curve is very slight. At 10 knots it gets 0.44 nmpg. At 40 knots it gets 0.30 nmpg.

At WOT however, Boats B and C both get better mileage than Boat A which only gets 0.25 nmpg. Should note that the engines in Boat A are both 8 cylinder. The engine in Boat B is a 6 cylinder and Boat C is a 12 cylinder.

These are all engines from the same manufacturer. However, different boat builders. Clearly the builder of B and C is interested in the top of the range while builder A is interested in lesser cruising speeds.

The only point here really is that things may not be as you'd expect. Just don't assume or go by what somebody said. See if the builder or a former seller of the boats has any performance charts.
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Old 03-07-2016, 12:58 PM   #85
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Ahhhhhh...actually designing a boat with power plant(s) in mind...what a concept!!!
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Old 03-07-2016, 04:14 PM   #86
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BandB,
Haha I knew you'd come up w something. Good job.
Sometime (mid 90's ?) big trucks seemed to get much more powerful and do it at considerably lower rpm. I suspect that had a lot to do w turbochargers and electronics.
I know it often goes the other way but you can't get around basic physics and all these engines are "heat engines" .... they make power from heat and heat loss is probably directly porportional to power loss. And of course some engines make better power than average at lower rpm and the reverse is (I believe) more often true. But there are many variables ...... and things often aren't as we expect.

You could make my small Mitsu make as much power as a Ford Lehman and w much lower heat loss most likely more efficient. However turbocharging would probably be necessary and the increased swept volume of air going through the engine would be increased heat loos as well ... that would be combined w the cyl surface area and combustion chamber loss. The total increased swept volume may make the little engine less efficient. Then there's the size of the cylinders v/s the # of cylinders ect ect. Interesting stuff but it usually leads one off into the fog.
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Old 03-07-2016, 04:27 PM   #87
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Haha I knew you'd come up w something. .
My advantage is I know nothing about engines. Nothing about the science. No idea how they do what they do. So, I can't get into the theory. What I have looked at over time is a lot of tests, a lot of data, on a lot of different boats. Sometimes the data seems to contradict conventional logic. So, for me, it's no labs, only real boats.

Sometimes ignorance is dangerous and sometimes bliss. Going back to the original question, we do oil change and all maintenance by the owner's manual or sooner if the trip we're ready to take would lead us past the due period. I know, from what others had said and the oil analyses, that we could probably go longer with no damage. I just choose not to. First, for warranty purposes. Then, simply because going by the manual has worked so well for me during the last 30 years or so.
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Old 03-07-2016, 04:28 PM   #88
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Pgitug wrote;
"This is a little off the mark, but to the extreme none of us have seen. I had a tech that drove his gas engine van 31,000 miles and only added oil when it was low. When the engine quit moving the mechanic took the oil out of the pan with a metal scraper."

This seems far fectched. Perhaps your "tec" was pulling your leg or chain?

However it opens the door to wondering how far a road vehicle could go w/o changing the full flow filter. If the oil stopped flowing one would'nt be very interested in changing oil. A road vehicle would fill it's oil filter much faster than a boat I would think. That adds to the notion that I have of the filter not needing replacement nearly as often as the oil. When I was a young man some of our old heaps burned/leaked so much oil that we never drained it assuming we were constantly changing oil. And we had by-pass filters.
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Old 03-07-2016, 05:42 PM   #89
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On the opposite end of oil-change schedules...

I was looking at the boat the other day. A bit under 800 hours on the engine over 6 years. The original owner has had the oil changed 2 to 3 times during that entire time! At first I thought I simply misunderstood him. Nope.
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Old 03-07-2016, 05:43 PM   #90
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I agree with "By the Book" in all pleasure boat applications. The savings in trying to extend oil life is not worth the risk of long term damage. And that is what its about - risk vs reward.

I used to work as operations manager for a company that had a fleet of many hundreds of Caterpillar 3516 generators. In this application, lubricating oil was one of our biggest operating costs. We extended the recommended oil life significantly, but took oil samples on engines daily towards the end of the oil life. In many cases we were able to get double the hours compared to "the book", but this varied considerably depending on many other factors.
A pleasure boat is a completely different story.
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Old 03-07-2016, 06:49 PM   #91
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Oil quality is paramount. By the book timing is the easiest to follow, but I really like O C Diver's method of total fuel burned as the best measure. In cold climes, where the boat will be stored over winter, The best time to change - after following fuel consumption or logged hours - is just before putting her up for the season. Getting all the contaminants out, and fresh oil in is the ultimate engine storage regime. No change needed in spring.

Can't wait to get back in!! (lakes are still frozen)
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Old 03-07-2016, 07:45 PM   #92
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Schaefferoil wrote;
"Oil quality is paramount"
I use RPM Delo as I belive it's a pluss to use a good oil. But you put so much emphisis on it you may be saying there's poor oil out there. I think it's kinda like cars and boat engines. They are all good but some are a little better.

As it's not recomended I think the "fuel burned" method may be OK most of the time or possibly even better. I could buy into it if it was done on an either-or basis.
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Old 03-07-2016, 07:56 PM   #93
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Just follow the engine manufacturer's recommendations. Why doesn't that settle the discussion?
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Old 03-07-2016, 08:00 PM   #94
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take 2 aspirin and call me in the morning....


an old joke but often we have seen it applicable in many situations.


while many manufacturer recommendations are good...are they good enough?
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Old 03-07-2016, 08:14 PM   #95
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No doubt, Nevertheless, some people enjoy endless discussion.
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Old 03-07-2016, 08:56 PM   #96
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The manufacturers recomendations may not be best for the product.

When I was flying ultralights I used racing synthetic lubricant. But it was not recomended by the engine manufacturer. They said they didn't have time to test all the different brands and types of synthetic lubricants. They sold their own brand of oil calling it Cuyuna 40-1 oil. The engine was a Cuyuna that was previously a snowmobile engine. I always used Bell-Ray two-stroke racing lubricant. Can't call it an oil because it wasn't ... nor is any other synthetic lubricant that's 100% synthetic. The Bell-Ray stuff was so viscous it could'nt be used w automatic oil injection systems as it was just too thick. But at very high temps thick and viscous is perfect.

So there are times when it's best to not follow the manufacturer's recomendations. But they are very few. I follow Mitsubishi's recomendation to use 30W dino oil.
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Old 03-07-2016, 09:02 PM   #97
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Quote:
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Just follow the engine manufacturer's recommendations. Why doesn't that settle the discussion?
I agree, to a point.

If a manufacturer suggests oil change intervals of say 200 hours and you only put 100 hours on your engine in a season, you won't change your oil at the end of the season? (OK, here in the Salish Sea we don't have seasons as such, but you get the idea).
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Old 03-07-2016, 09:06 PM   #98
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Mark,
I see you enjoy the conversation enough to be here.
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Old 03-07-2016, 09:08 PM   #99
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Dave...Exactly the point...it is not that some of us are trying to ignore manufacturers recommendations or trying to be smarter than them...


But as I posted...if engine manufacturers suggest oil changes for "harsh conditions" on one level such as diesel trucks in certain conditions...but only give one recommendation for marine engines (often run in conditions all over the map so to speak by different owners)...then who are they BSing?...there must be flexibility in their recommendations or life just doesn't make sense from one arena to the next.


I would like to think I am one of the educated consumers...not one of the sheep.
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Old 03-07-2016, 09:11 PM   #100
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Mark,
I see you enjoy the conversation enough to be here.
Actually, it has been an irritation. Itches need to be scratched. Regardless, we just change the oil annually with an average of 120 engine-hours.
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