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Old 08-23-2013, 07:46 AM   #41
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I agree! Too much emphasis is placed on slowing way down to save fuel. When we drive our cars, most of us go the speed limit or more but when we get in our boats, then we decide it's time to save money???

Yes, too much is made of seeing who has the least fuel burn. I'm not impressed with any of it.
You must not drive a Super Duty pickup truck.. Many times I keep it at 60 instead of 75 like the traffic allows and I save 25% in fuel costs.

Sure it doesn't matter going a mile or two to the store...just like on a boat it doesn't matter at 50-100hrs a year...start cruising 300-500 hrs a year (or burning over 3000 galons/year) and it starts to matter as does it can mean just making the next fuel stop.

None of it's meant to impress any more than some of the REAL nonsensensical threads on this sight...like smoothest engines....discussing fuel consumption issues are just to let the less informed that cruising boats save significantly when run certain ways.

Most of the old timers hardly need to be on this forum having already formed their opinion (right or wrong) and probably aren't going to change ant boating habits (even when pretty reliable, factual sources are linked).
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Old 08-23-2013, 11:39 AM   #42
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The difference between 6.3 (a knot below hull speed) and 7.3 knots can be on the order of 75% increased fuel use.
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Old 08-23-2013, 12:02 PM   #43
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Most of the old timers hardly need to be on this forum having already formed their opinion (right or wrong) and probably aren't going to change ant boating habits (even when pretty reliable, factual sources are linked).
I disagree with your sweeping denouncement of our respected elders. Most of the folks I've met here, old and young, seem to be willing and eager to share what they know and learn from others' experiences.

Do you include yourself as "most of the old timers"?

I'm not one of 'em yet, although I may resemble that remark.
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Old 08-23-2013, 12:32 PM   #44
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I disagree with your sweeping denouncement of our respected elders.
My statement that I think too much is made of going slow stems mainly from the fact that most of my cruises beyond 50 miles (one way) were done when I was paying $1/gallon. Now, that fuel is sky high, I don't go nearly as far. I still believe, however, that too much is made of going slow. I use to make the trip to Catalina in 3.5 hours. (Ocean Alex @ 20 knots) In my present boat it would take me 8.5-9.0 hours. With me it's the destination not the journey.
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Old 08-23-2013, 12:59 PM   #45
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The Eagle is to slow and one of hundred of reason we do not leave the dock much. Ok, seldom! I personal what to buy a go very fast boat, but my wife wanted the ugly slow trawler, which has made a great live a board. Being we both work and family, friends and personal stuff take up most week ends and vacations. At least every month we are fly/going someplace. Besides since we live on the boat why in the heck would we want to take a vacation on it?

The plan when we retire is to move the boat around the PNW as we will not be tied to one area. We been talking about moving the boat to where its drier and warmer. PNW can be so damp and depressing!
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Old 08-23-2013, 01:01 PM   #46
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I disagree with your sweeping denouncement of our respected elders. Most of the folks I've met here, old and young, seem to be willing and eager to share what they know and learn from others' experiences.

Do you include yourself as "most of the old timers"?

I'm not one of 'em yet, although I may resemble that remark.
We seem to disagree then.

My opinion didn't denounce anyone...that's YOUR interpretation of my comment.

"old timers" doesn't necessarily have anything to do with age.....
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Old 11-09-2015, 11:06 PM   #47
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Some of us have limited budgets, some of us don't.
Some of us have tight schedules, some of us don't.
Some of us have go slow boats, some of us don't.
Some of us see each other as old, some of us don't.
It's what makes the world go 'round.

If you play or cruise or live or do whatever on a boat... you're luckier or crazier (or both) than most. We only come by once, and only for a short ride. Enjoy the heck out of that ride, however you see fit.
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Old 11-09-2015, 11:14 PM   #48
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PNW can be so damp and depressing!
Please, just keep saying that, will you?
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Old 11-09-2015, 11:18 PM   #49
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Going slow is peaceful.

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Old 11-10-2015, 12:08 AM   #50
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In Boating - Simply Going Is Life Extending... At Any Speed!

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Old 11-10-2015, 12:18 AM   #51
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I agree with Art, being out there and enjoying the day is the biggest plus, regardless of what speed you are doing.
Every one has different agenda when it comes to boating, so maybe if we are happy in ourselves for what we enjoy and can afford , than that is all that matters.

I just wish I was boating in the states where Fuel is so Cheap !!!

Cheers Chris D Liberty
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Old 11-10-2015, 01:53 PM   #52
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I would like everyone's (or anyone's) opinion on what is too low an rpm for diesel engines. Do I understand it that manufacturers set a suggested cruising speed at around 75-80% of WOT? I realize that there is a minimum temperature required to burn the fuel completely, but is temperature the only restriction? On the following engine for example:
Detroit Diesel 12V71N
WOT is 2300 rpm and fuel burn is 28 gph
at 78% (cruising speed) rpm is 1800 rpm with a fuel burn of 14 gph
at 52% rpm is 1200 rpm with a fuel burn of 6 gph

My question is, if the engine temperature stays above 150 or so, can you cruise at 1200 rpm without damaging the engines? I'm asking about long term damage if you chose to cruise at these reduced speeds throughout the life of the engine. Obviously, you would need to blow them out for a few minutes periodically throughout each cruise.
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Old 11-10-2015, 03:48 PM   #53
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The 75-80% figure is mostly related to engine longevity. For a lot of engines you might even be able to run 90% WOT continuously. What the engine guys are warning about is don't try and run near WOT for extended periods.

A comfortable cruise speed is more boat hull & weight related, and it might be at a much lower engine power level than 80%.

For DD's, they get their best performance (fuel efficiency and longevity) when reasonably loaded up. Running them at low loads is not ideal, but I think there are quite a few owners here who do and have not had the sky fall in. One of them can comment on the 52% load level but doing that with a run-up from time to time is pretty common practice. I think that if you have DD's then running on just one engine at slow speeds, in order to load the other one up a bit more, does have merit if your hull still behaves ok.
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Old 11-10-2015, 04:25 PM   #54
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Yes !

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In Boating - Simply Going Is Life Extending... At Any Speed!

Very true ! I like that.
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Old 11-10-2015, 05:37 PM   #55
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Fifty two % of rpm is only 15 or 20 % load.

18-1900rpm may be 50% load. depends on what rpm you burn 50% of the maximum amount of fuel your engine can burn under a propper load.
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Old 11-10-2015, 06:59 PM   #56
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The 75-80% figure is mostly related to engine longevity. For a lot of engines you might even be able to run 90% WOT continuously. What the engine guys are warning about is don't try and run near WOT for extended periods.

A comfortable cruise speed is more boat hull & weight related, and it might be at a much lower engine power level than 80%.

For DD's, they get their best performance (fuel efficiency and longevity) when reasonably loaded up. Running them at low loads is not ideal, but I think there are quite a few owners here who do and have not had the sky fall in. One of them can comment on the 52% load level but doing that with a run-up from time to time is pretty common practice. I think that if you have DD's then running on just one engine at slow speeds, in order to load the other one up a bit more, does have merit if your hull still behaves ok.
I've yet to find a DD mechanic, and I've met several old timers, who can remember one failing due to going too slow. No load is the problem and not recommended. Yeah you run them up for 15 minutes at the end of a day's slow run, or maybe the next day's slow run or heck just every now and then. Our 8v92ti's spent almost all their life between 1000 and 1300 rpm and surveyed beautifully at 3000+ hours.
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Old 11-10-2015, 07:11 PM   #57
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Originally Posted by Cuttyhunk47 View Post
I would like everyone's (or anyone's) opinion on what is too low an rpm for diesel engines. Do I understand it that manufacturers set a suggested cruising speed at around 75-80% of WOT? I realize that there is a minimum temperature required to burn the fuel completely, but is temperature the only restriction? On the following engine for example:
Detroit Diesel 12V71N
WOT is 2300 rpm and fuel burn is 28 gph
at 78% (cruising speed) rpm is 1800 rpm with a fuel burn of 14 gph
at 52% rpm is 1200 rpm with a fuel burn of 6 gph

My question is, if the engine temperature stays above 150 or so, can you cruise at 1200 rpm without damaging the engines? I'm asking about long term damage if you chose to cruise at these reduced speeds throughout the life of the engine. Obviously, you would need to blow them out for a few minutes periodically throughout each cruise.
I like to run my 3208 cats at 1200 rpm burning 4 gal/hr @ 7 kts (160 degrees). I can barely hear them running. Every few hours I run them up to 2000 rpms for 5-10 minutes. I only get about 11 kts at that rpm. When I throttle up a blue puff of smoke comes out but clears quickly. Engines heat up to 175-180 degrees and all is well. The wind is more and isenglass flaps around and its louder. I like slow better. I have a great mechanic (Ski on this forum) which instructed me to do this.
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Old 11-10-2015, 08:27 PM   #58
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Some of you may have heard this from me before. It is my explanation of why I run slow.
I am simplifying the numbers as fractions are difficult to follow.

We have a number of jumps which are approximately 65 nm. Generally I do these at 6.5 kts, way down from our higher cruise speed of 8kts.

However at 6.5kts we burn two gallons per hour, at 8kts it is close to four gph, almost double.

Thus for a 65 mile trip:

6.5 kts, 10hrs, 20 gallons burned at $6 per gallon (Caribbean prices) $120 US
8 kts, 8 hrs, 32 gallons burned at $6 per gallon, $192 US

Since we will leave at approximately 6 am in all conditions, the difference in arriving at 2 pm, or 4 pm is $72 US, more than enough to buy us dinner.

This may or not be important to all of us, but I consider it a free meal for an extra two hours of watching the world go by.
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Old 11-10-2015, 09:22 PM   #59
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I have a great mechanic (Ski on this forum) which instructed me to do this.
You're a lucky man! I wish I had a Ski on the left coast.

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This may or not be important to all of us, but I consider it a free meal for an extra two hours of watching the world go by.
Shucks....2 more hours in that KK42. Don't you hate it when that happens?
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Old 11-10-2015, 09:39 PM   #60
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...
Since we will leave at approximately 6 am in all conditions, the difference in arriving at 2 pm, or 4 pm is $72 US, more than enough to buy us dinner....
As I said a few days ago.
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