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Old 10-31-2015, 01:16 PM   #161
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I have read this entire thread and am thoroughly scratching my head. The numbers are all over the place. Some folks may not be measuring/doing the match correctly. Applying the bell curve theory I have arrived at some numbers for chainsaw math.

I do know that when the day comes, I will be installing fuel flow meters and carefully plotting some numbers in still water.
Oscar- What you are seeing are the differences between a vast range of boats in size, weight, and design speed. Some are as small as in the 20-30 foot range, weighing a few to several thousand pounds, up to over 60 feet and weighing in the 50,000 to 80,000 pound range.

Add to that the differences between hull styles: Full displacement, which is slow but very efficient at slow speeds. Semi planing, which is a compromise between efficient slow speed, yet decent capability at slow planing speed. And then fast planing, which are light, or should be light, and have lots of power for running 20kts plus.

So between the vast range of size and weights, and the wide range of design speeds, the fuel burn numbers will be all over the map.

Just scanning through this thread last night, the numbers folks posted seemed to make sense for their specific boat.
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Old 10-31-2015, 01:41 PM   #162
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Oscar- What you are seeing are the differences between a vast range of boats in size, weight, and design speed. Some are as small as in the 20-30 foot range, weighing a few to several thousand pounds, up to over 60 feet and weighing in the 50,000 to 80,000 pound range.

Add to that the differences between hull styles: Full displacement, which is slow but very efficient at slow speeds. Semi planing, which is a compromise between efficient slow speed, yet decent capability at slow planing speed. And then fast planing, which are light, or should be light, and have lots of power for running 20kts plus.

So between the vast range of size and weights, and the wide range of design speeds, the fuel burn numbers will be all over the map.

Just scanning through this thread last night, the numbers folks posted seemed to make sense for their specific boat.
Agreed!
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Old 10-31-2015, 02:07 PM   #163
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Agreed!
Wifey B: Yeah I could post my play fun fave open it up Baby Riva. WOT is 43 knots, 72 gph, 0.60 nmpg. But I can pull back and slow down to 36 knots, 53 gph and 0.68 nmpg. Oh and 1000 rpm is 11 knots, 14 gph, 0.79 nmpg.
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Old 10-31-2015, 02:25 PM   #164
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Wifey B: Yeah I could post my play fun fave open it up Baby Riva. WOT is 43 knots, 72 gph, 0.60 nmpg. But I can pull back and slow down to 36 knots, 53 gph and 0.68 nmpg. Oh and 1000 rpm is 11 knots, 14 gph, 0.79 nmpg.
Or you could anchor and swim/play for "0" nmp "0" g
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Old 10-31-2015, 02:37 PM   #165
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Or you could anchor and swim/play for "0" nmp "0" g
Wifey B: Could....then go fast to make up for lost time... Or just wait for The Great Pumpkin. It's coming tonight, Charlie Brown.
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Old 10-31-2015, 05:39 PM   #166
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6.7 knots at 1700 rpm on Perkins 6.354. That nets around 3 nmpg. Seems to run happiest there.
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Old 10-31-2015, 05:59 PM   #167
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Perkins 6.354. 3 liters a hour @ 6.8 knots on the iPad at 1200 rpm harmonics are smooth and pleasant to live with putting out near no wake until I get up to 10 knots at 1800 rpm
11 knots a 2200 rpm bum digs in wake big enough to wake board off

I still think my figures are wrong it cant use that little can it ?
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Old 10-31-2015, 06:06 PM   #168
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Perkins 6.354. 3 liters a hour @ 6.8 knots on the iPad at 1200 rpm harmonics are smooth and pleasant to live with putting out near no wake until I get up to 10 knots at 1800 rpm
11 knots a 2200 rpm bum digs in wake big enough to wake board off

I still think my figures are wrong it cant use that little can it ?
Sure it can. How much does it weigh?
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Old 10-31-2015, 06:27 PM   #169
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Twin 3116 Caterpillar 300 HP

9.8 knots at almost 1600 RPM.
20 liters per hour for both engines. Clean hull.
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Old 10-31-2015, 06:30 PM   #170
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RPM at 9.8 knots

Almost 1600 RPM / 9.8 knots

Sorry I don't know know to send 2 pics in the same message.
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Old 10-31-2015, 06:31 PM   #171
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Perkins 6.354. 3 liters a hour @ 6.8 knots on the iPad at 1200 rpm harmonics are smooth and pleasant to live with putting out near no wake until I get up to 10 knots at 1800 rpm
11 knots a 2200 rpm bum digs in wake big enough to wake board off

I still think my figures are wrong it cant use that little can it ?

My boat does in the same range. 6.3 knots. And about (approximately) 3 L /hr. 30', 13,500 lbs.

I have not (don't have the patience for) tried idle (approx 4.5 knots) for any period to see what the fuel burn is. I have lots of time on my hands..... But not that much patience.
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Old 10-31-2015, 06:35 PM   #172
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Sure it can. How much does it weigh?


Displacement 4.5 Tonne and just added 250kg lead to the stern which I think was missing or stolen
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Old 10-31-2015, 06:41 PM   #173
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7.9 knots

Almost 1100 RPM / 7.9 knots
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Old 10-31-2015, 06:48 PM   #174
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Idle

5 knots at idle.
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Old 10-31-2015, 07:16 PM   #175
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1500 RPM seems to give 7.5 knots to 10 knots SOG depending on current at about 5-6 GPH fuel burn...I generally plan on 7.5 knots for slightly more than 1 NMPG.

And after a bit it becomes time to clear the engines at 2300 RPM...for some reason I've never bothered to calculate the fuel burn at that RPM.
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Old 11-04-2015, 07:44 PM   #176
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7.5 kts at 1,800 rpm, 1.8 USG/hour, 4.2 nm/USG. KK42 full displacement, FL135 hp.


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Old 11-04-2015, 09:48 PM   #177
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I have two boats.. On the boat in my avatar (1936 Nunes Brothers 33 with a 2011 Volvo-penta D2-40) I like to run at about 2000-2050 rpms which gives me about 7 knots at 0.55 gallons per hour (12.7 mpg). However, my wife prefers that I run at about 1,600 rpms for about 5.5 knots at about 0.25 gallons per hour (22 mpg).This summer I averaged 0.4 gph. I can do just over 9 knots wide open throttle.

On my other boat (Allied 36 with a Westerbeke 46), I cruise at 6 knots at 1,500 rpms and averaged 0.43 gph this season (14 mpg). I can make about 7.5 knots at 3,000 rpms at almost 3 gph. I can also make 6-7 knots at 0 gph if the wind is right. Yes it is a sailboat .
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Old 11-04-2015, 11:53 PM   #178
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I have two boats.. On the boat in my avatar (1936 Nunes Brothers 33 with a 2011 Volvo-penta D2-40) I like to run at about 2000-2050 rpms which gives me about 7 knots at 0.55 gallons per hour (12.7 mpg). However, my wife prefers that I run at about 1,600 rpms for about 5.5 knots at about 0.25 gallons per hour (22 mpg).This summer I averaged 0.4 gph. I can do just over 9 knots wide open throttle.

On my other boat (Allied 36 with a Westerbeke 46), I cruise at 6 knots at 1,500 rpms and averaged 0.43 gph this season (14 mpg). I can make about 7.5 knots at 3,000 rpms at almost 3 gph. I can also make 6-7 knots at 0 gph if the wind is right. Yes it is a sailboat .
"5.5 knots at about 0.25 gallons per hour (22 mpg)." Really, four cups per hr to move many tons 5.5 nm through the water! That's unbelievably efficient!
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Old 11-05-2015, 01:11 AM   #179
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"5.5 knots at about 0.25 gallons per hour (22 mpg)." Really, four cups per hr to move many tons 5.5 nm through the water! That's unbelievably efficient!
Wifey B: We don't get that in our cars.
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Old 11-05-2015, 01:35 PM   #180
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Yea, calling BS on TDunn's Volvo burn numbers. Beautiful old boat, kudos there, but a 2liter engine running 2000rpm pushing a 33footer is going to burn more than 0.55gph.

My 2liter tdi vw cruises down the road at about 2000rpm and 60mph and gets 50mpg. That's a bit above 1gph. Much easier to push than a 33foot boat at 7kts.
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