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Old 10-31-2015, 09:02 AM   #41
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Old 10-31-2015, 09:04 AM   #42
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Quote:
Originally Posted by neworleansrich View Post
My friend and I have been running our boats from New Orleans to the Bahamas for years. He has a 61ft Hataras with 12-71s. This last trip he put a feathering prop on one side, giving him a maneuvering/ get home engine on that side. The boat cruises at 8kts about 20-30% more efficiently running on a single engine with the feathering prop. Honestly, if you don't run long distances, it does not matter, but for our trips where we'll burn several thousand gallons over a cruise, it does add up. One of the biggest benefits on a long cruise is not needing to change oil on the feathering side.

On my Defever 48 I have 3208s. I will install a feathering prop on the port side next month when I haul out.
That is interesting. What happens on your DF will be good to know. The 3208s are a lot of engine for the 48.

We normally cruise at 7.8 to 8.1 yielding 4.6 gph (tank fill basis) including genset and diesel heat. Engines are PS rated at 225 and we pull less than 60 hp from each on average. The vessel will cruise nicely at 8.8kts with a bump from around 1750 to 2000 rpm.
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Old 10-31-2015, 10:36 AM   #43
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I rarely participate in threads like this, for the simple reason that the answer requires a lot more diligence than most folks are willing or able to give it. A person claims a certain improvement that lies within a range where environmental factors may have a greater impact, and therefore the person claiming has little ability to separate their desired conclusion. Many are well intentioned, and enthusiastic.

Then we have the multiple discussions, one topic examples. Since I have not heard it yet, I'll give the example. Eventually someone will claim that when they ran on one engine, their consumption was cut by almost 75%. Because when they went from 20 knots on both to 7knots on one engine... Actually saw that on another forum. Examples that will come from entirely different discussion points, all grouped into one analysis.

Suffice to say, the challenge here is not just that different boats behave differently, but that the amount of measurable difference is small. I think by the way, that's the general point and conclusion. Running on one engine, in an otherwise identical environment, will have an eventually measurable increase in efficiency for many boats, but the difference will be small. Small enough to be worth a more wholistic consideration as to its benefit in a given situation, such as wear and tear, etc.. That's not the clean cut conclusion most are wanting to jump to.

There is another thread I'm resisting contributing to on the topic of fire related boat statistics, as the data is so intentionally incomplete and poorly populated with dimensional slicers that anybody with a background in data analysis would raise a few eyebrows. Archetypical for all the wrong reasons.

I'm a data architect/data scientist and have spent 20+ years organizing and working with large datasets. The first clue when trying to figure out who knows what they are talking about with statistical data is to look for opinions with high levels of confidence. The louder and more confident that you hear a definitive conclusion, the more likely it is that you should ignore the persons opinion and look deeper.
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Old 10-31-2015, 10:43 AM   #44
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Some say they burn less running single on a twin and some say otherwise.
But since it apparently is worth talking about indicates to me that it's a big case for running a smaller engine in either singles or twins.

When skippers run a single on a twin is essentially cutting the size of your engine in half. And when they do they predominately burn less fuel even with the asemetrical thrust and drag of the dead prop. It's obvious that without the two huge elements of drag the boat with less engine burns less fuel. So small engines running harder seem to rule.
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Old 10-31-2015, 11:04 AM   #45
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The first clue when trying to figure out who knows what they are talking about with statistical data is to look for opinions with high levels of confidence. The louder and more confident that you hear a definitive conclusion, the more likely it is that you should ignore the persons opinion and look deeper.
Well said. The more data, qualifiers and disclaimers that accompany the data the more I'm interested. (As in:"Show your work")
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Old 10-31-2015, 12:00 PM   #46
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And how about CALIBRATED fuel flow measurement for each engine without which this thread largely falls flat and reverts to opinions.
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Old 10-31-2015, 01:09 PM   #47
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Tom,
Most just use hour meter readings and gallons they squirt in the hole. So much time is spent by most everybody at idle or other speeds slower than normal cruise speeds most gph postings are way off.

The only time I was close was running from AK to WA and keeping track of time run at less than cruise speed and subtracting that from total time. Then how much I squrited in the hole had real meaning .. but still off.
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Old 11-04-2015, 11:40 AM   #48
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The difficulty of reaching any conclusion here is that people have tried different approaches. Commonly they try to maintain the same speed on one engine. In my case that was not reasonable. Too much steering offset. If I slowed down to a speed where steering was reasonable the fuel use declined measurably. Speed went from about 9 knots to ablur 6.5. fuel went from 2 NMPG to about 3 NMPG. A problem was going far enough to really measure use. My 120 Mile trip no doubt had inaccuracies in fillup measurements, nevertheless I found a benefit.
The unanswered question fundamental to the discussion is what would the fuel use be at the same low speed on two engines. No doubt it would also be significantly lower however at that speed both engines were just above idle so I felt it better to load one engine a bit more than run one at very low load.


My conclusion is that were I to make an extended offshore trip where range was paramount.I would run at lower speed on one.
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Old 11-04-2015, 05:06 PM   #49
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Quote:
Originally Posted by ghost View Post
I rarely participate in threads like this, for the simple reason that the answer requires a lot more diligence than most folks are willing or able to give it. A person claims a certain improvement that lies within a range where environmental factors may have a greater impact, and therefore the person claiming has little ability to separate their desired conclusion. Many are well intentioned, and enthusiastic.

Then we have the multiple discussions, one topic examples. Since I have not heard it yet, I'll give the example. Eventually someone will claim that when they ran on one engine, their consumption was cut by almost 75%. Because when they went from 20 knots on both to 7knots on one engine... Actually saw that on another forum. Examples that will come from entirely different discussion points, all grouped into one analysis.

Suffice to say, the challenge here is not just that different boats behave differently, but that the amount of measurable difference is small. I think by the way, that's the general point and conclusion. Running on one engine, in an otherwise identical environment, will have an eventually measurable increase in efficiency for many boats, but the difference will be small. Small enough to be worth a more wholistic consideration as to its benefit in a given situation, such as wear and tear, etc.. That's not the clean cut conclusion most are wanting to jump to.

There is another thread I'm resisting contributing to on the topic of fire related boat statistics, as the data is so intentionally incomplete and poorly populated with dimensional slicers that anybody with a background in data analysis would raise a few eyebrows. Archetypical for all the wrong reasons.

I'm a data architect/data scientist and have spent 20+ years organizing and working with large datasets. The first clue when trying to figure out who knows what they are talking about with statistical data is to look for opinions with high levels of confidence. The louder and more confident that you hear a definitive conclusion, the more likely it is that you should ignore the persons opinion and look deeper.
It seems you occupy the moral high ground? But then you make statements without any data to support it, highlighted in red. Ironic that you go on to talk about jumping to conclusions!

In post #6 I attached a graph showing Dreamer's data (link to webpage also) and my own sea trials. The result is the opposite of your conclusion. My data was from the John Deere fuel flows that I log and cross-check against fuel fills. Two boat are not many, but the data is real.

Now there have been posts about boats with large DD engines running slow. Easy to believe their claims that running on one is more efficient (at the same speed) because the higher the load the less fuel those engines slobber. In conjunction with Eric's comment about smaller engines, this leads me to suspect that the more power a boat has installed then the more likely it is that running on one engine at a given displacement speed will use less fuel. Just a suspicion, I'd like to see more data before making pronouncements!
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Old 11-05-2015, 10:05 AM   #50
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I won't be contributing here any more. This is exactly why. Thx
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Old 11-05-2015, 10:49 AM   #51
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Maybe he was just a ghost.

Sure liked some of his past posts.

Indeed bigger engines would clearly have greater need (I use the ward lightly) to run on one engine. If they (engines) were small enough even running at light load would not be desired or likely.

With my own boat I'd have to run one engine (assuming two 20hp engines instead of one 40) full bore to achive my normal cruise speed .. if it was possible. And conversely if I had 70hp (twin 35's) I'd be very inclined to run on one. 36hp is what Willard provided for the boat and the W30 is one of the rare boats not overpowered.

But talking about power on a FD boat has it's limitations when most all the other club members run SD boats. But comparisons are interesting often lead us to truths.
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