What's your cruising speed.

BoatUS magazine featured a Back Cove 41 this month. The author stated, apparently with a straight face, " throttle back a bit and she'll happily cruise all day at 22 knots burning a respectable 25 gallons per hour." That's respectable for a 41 with a single?

drb1025 said:

BoatUS magazine featured a Back Cove 41 this month. The author stated, apparently with a straight face, " throttle back a bit and she'll happily cruise all day at 22 knots burning a respectable 25 gallons per hour." That's respectable for a 41 with a single?

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Here are some Back Cove numbers I found.

With a 600 hp Cummins. 18 knots at 19 gph. 22 knots at 25 gph. WOT is 27 knots at 32 gph. 7.2 knots at 1.5 gph.

With a 715 hp Cummins. 21 knots at 23 gph. 24 knots at 27 gph. WOT is 29 knots at 38 gph. 8.5 knots at 4.1 gph.

Oh and at 22 knots, range is around 320 nm so will cruise all day.

Typically 1060 rpm, which gives an average of 8.6 knots (maybe 8.7) at about 7 gph. Lately, I have been bumping up to about 1250 rpm which gives 10 knots but at about 11 gph. Rarely slower, although at about 6.5 knots and 800 rpm I burn less than 4 gph.

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.

We cruise at 6.15 knots.

What's all this talk about engine rpm? What has it to do w anything.
Fuel consumption is highly related of course.

I am sure I have replied somewhere in this thread but......17 knots at about a gallon a mile...or 16gph

djones:
We Saltspring Islanders should band together.
Where are you on SSI?
I look out on Convoer Cove.

Baker said:

I am sure I have replied somewhere in this thread but......17 knots at about a gallon a mile...or 16gph

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Yup - that's the ticket! ! Our twin screw gasser Tolly averages same mpg at same speed.

If we want to go slow on twins - i.e. just under calced 7.58 knts hull speed (e.g. 6.5 to 7 knts) we gets near 2 nmpg. Really s-l-o-w (5 +/- knts) on one engine with dead prop left in freewheel (BW trany allows that and no dripless on shaft) we can get upwards of 2.75 nmpg.

Can't beat those "fun" numbers with a stick! - So to say!! LOL

Hey Baker - No Mermaid picts recently - What up??

oscar said:

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.

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All the numbers I have quoted are from performance tests. None estimated. Anytime I quote any of our numbers it's metered and then verified by then matching fills to projected fills.

8.7 Kts or 10 mph when cruising. About 2.5 mpg running at 1350 rpm

oscar said:

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.

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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.

Ski in NC said:

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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Agreed!

Art said:

Agreed!

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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.

BandB said:

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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Or you could anchor and swim/play for "0" nmp "0" g

Art said:

Or you could anchor and swim/play for "0" nmp "0" g

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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.

6.7 knots at 1700 rpm on Perkins 6.354. That nets around 3 nmpg. Seems to run happiest there.

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 ?

gaston said:

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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Sure it can. How much does it weigh?

Twin 3116 Caterpillar 300 HP

9.8 knots at almost 1600 RPM.
20 liters per hour for both engines. Clean hull.

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.

gaston said:

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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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.

High Wire said:

Sure it can. How much does it weigh?

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Displacement 4.5 Tonne and just added 250kg lead to the stern which I think was missing or stolen

7.9 knots

Almost 1100 RPM / 7.9 knots

Idle

5 knots at idle.

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.

7.5 kts at 1,800 rpm, 1.8 USG/hour, 4.2 nm/USG. KK42 full displacement, FL135 hp.


Jim
Sent from my iPad using Trawler Forum

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 .

TDunn said:

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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"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!

Art said:

"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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Wifey B: We don't get that in our cars.

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.