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Old 03-08-2016, 08:40 PM   #1
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What is your mpg, gallons per hour etc... at various speeds?

I would like to know some specifics on your engine fuel usage, and also what type hull, displacement, semi displacement, planing, single engine or twin and whether it is gas or diesel.
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Old 03-08-2016, 09:20 PM   #2
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Semi displacement 44' WLL, 47' LOD, 53' OAL
Twin 330 HP Cummins diesels
1.75NMPG at 8 knots
1.5NMPG at 9 knots (thoeretical hull speed)
.75NMPG at 14 knots

440 gallons of fuel
Safe range over 600NM
(Farthest distance in North America between fuel stops 260NM)

These measurements were taken using Floscan fuel computers and are within 10% based on totalizer readings vs actual fuel fill ups over a period of several seasons.
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Old 03-08-2016, 09:20 PM   #3
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John Deere 4045TFM75 135 HP
45' Semi Displacement 40,000 lbs.
Single Diesel

6.0 knots 1.2 GPH 5.0 NMPG Slow cruise, no wake
7.0 Knots 1.9 GPH 3.7 NMPG Normal cruise, very modest wake
8.0 Knots 3.2 GPH 2.5 NMPG Fast cruise to beat the weather, big wake
9.0 Knots 6.0 GPH 1.5 NMPG Flank emergency only! Surfs up

Ted
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Old 03-08-2016, 10:52 PM   #4
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Ignorant sailor question....

Are those numbers y'all quoted taken from fuel vs hours calculations or taken from a fuel burn indicator via the engines instruments? Wondering how accurate those engine instruments are....
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Old 03-08-2016, 11:02 PM   #5
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Cummins 6BT5.9 210HP, LWL: 34.7', 31000 lbs, semi-displacement

The following operating hours and ranges are based on continuous running and calibrated fuel flow (FloScan). NM/G and ranges can increase up to 20% assuming 4 hour average daily runs and normal times for warming/cooling.

Really Slow Economy cruise: 1400 rpm, 6.2 kts, S/L 1.06, 59.2% propeller efficiency, 28 hp (13% of ME rating), 1.7 gph, 3.7 nm/g, 172 F coolant temp, 380 F pyro, 1.0 lb turbo boost, 195 operating hours with a range of 1207 miles (90%), 74 dba in pilothouse.

Slow Economy cruise: 1500 rpm, 6.5 kts, S/L 1.11, 58.8% propeller efficiency, 34 hp (16% of ME rating), 2.1 gph, 3.1 nm/g, 172 F coolant temp, 420 F pyro, 1.5 lbs turbo boost, 158 operating hours with a range of 1024 miles (90%), 77 dba in pilothouse.

Fast Economy cruise: 1600 rpm, 6.9 kts, S/L 1.18, 58.6% propeller efficiency, 41 hp (20% of ME rating), 2.5 gph, 2.8 nm/g, 172 F coolant temp, 450 F pyro, 2.0 lbs turbo boost, 132 operating hours with a range of 914 miles (90%), 78 dba in pilothouse.

Slow Fast cruise: 1700 rpm, 7.2 kts, S/L 1.23, 57.5% propeller efficiency, 47 hp (22% of ME rating), 2.9 gph, 2.5 nm/g, 173 F coolant temp, 480 F pyro, 2.5 lbs turbo boost, 114 operating hours with a range of 822 miles (90%), 77 dba in pilothouse.

Fast cruise: 1800 rpm, 7.5 kts, S/L 1.28, 56.6% propeller efficiency, 55 hp (26% of ME rating), 3.5 gph, 2.1 nm/g, 175 F coolant temp, 510 F pyro, 3.3 lbs turbo boost, 95 operating hours with a range of 709 miles (90%), 74 dba in pilothouse.
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Old 03-08-2016, 11:12 PM   #6
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Quote:
Originally Posted by dhays View Post
Ignorant sailor question....

Are those numbers y'all quoted taken from fuel vs hours calculations or taken from a fuel burn indicator via the engines instruments? Wondering how accurate those engine instruments are....
Newer diesel engines have electronically controlled injection as opposed to the old style mechanically controlled injection. The control is very precise making it easy to calculate theoretical fuel flow as opposed to actually measuring fuel flow. My engine display has a real time fuel consumption display to 1/10 GPH and total fuel consumption counter. On my recent 1,200 mile trip, I kept fairly detailed notes on fuel consumption and fuel purchased. The numbers match well with what the display is telling me. I believe the accuracy is within 2/10 GPH.

Ted
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Old 03-08-2016, 11:13 PM   #7
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Here's what I measured a while back in calm waters. Range in nm is with 10% reserve (1200 gal fuel on board).

1996 John Deere 6068T

1000rpm 4.8kt 4.0nmpg 4300nm
1200rpm 5.7kt 3.2nmpg 3400nm
1400rpm 6.7kt 2.7nmpg 2900nm
1600rpm 7.4kt 2.2nmpg 2300nm
1800rpm 7.9kt 1.4nmpg 1500nm
2000rpm 8.9kt 1.2nmpg 1300nm
2200rpm 9.4kt 0.9nmpg 950nm (WOT)

My "hull speed" is 9.3kt - with a full displacement design and 80,000lb full load the numbers seem reasonable.

In practice I expect that sea state will reduce these numbers. Also currents can be surprisingly large in the ocean (and always against you of course!) I've been following m/v Dirona with interest - and would plan to use a fuel bladder for long ocean passages as they have done. I could easily add 400 gal of fuel that way and give me peace of mind for a long crossing. I hope to go to the South Pacific via Hawaii at some point. I'll need to make 2200nm or so with this plan.

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Old 03-08-2016, 11:17 PM   #8
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38' LOA 35' LWL 11.8' beam 14000lb wet weight, 450hp Cummins 6CTA

Slow cruise 7.7kt 950rpm 1.9gph

Fast cruise 20kt 2000rpm 11gph

Top end 29kt 2700rpm 24gph

Modified Vee hull, single screw, 1.514:1 gear, 24x23 3b wheel

Slow and fast cruise gph numbers calculated from tank dipstick readings over many trips totalling over 15000nm.

320gal capacity, 1200nm range slow, 545nm fast considering 300gal usable.
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Old 03-08-2016, 11:17 PM   #9
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Quote:
Originally Posted by dhays View Post
Ignorant sailor question....

Are those numbers y'all quoted taken from fuel vs hours calculations or taken from a fuel burn indicator via the engines instruments? Wondering how accurate those engine instruments are....
My numbers are using my Flo Scan. I don't know how accurate it is - I'll have to run some tests on that before betting my life on the results!

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Old 03-08-2016, 11:34 PM   #10
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Quote:
Originally Posted by dhays View Post
Ignorant sailor question....

Are those numbers y'all quoted taken from fuel vs hours calculations or taken from a fuel burn indicator via the engines instruments? Wondering how accurate those engine instruments are....
My numbers are from flow scan fuel flow meters.

They are within 10% based on my fuel fill ups vs the readings.
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Old 03-08-2016, 11:36 PM   #11
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After crunching the numbers from our first year, including warm ups & cool downs, anchoring, crabbing, and putzing around with whales and wildlife we averaged 1.3 US gallons per hour.

30' semi displacement, 11' beam, 3.5' draft. Somewhat overpowered...PO replaced original 65 hp with a 100 hp Yanmar 4JH2-UTE.

Usually run at 2700 rpm because it sounds happiest there and make somewhere between 6 and 8 knots (ish) depending on tidal currents.

PO also installed an extra fuel tank for a total of 140 gallons, giving us the ability to roam around in remote areas longer without having to come all the way back in to fuel up.
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Old 03-08-2016, 11:38 PM   #12
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LWL 46' 4"
LOA 51' 6" (excl swim grid)
Beam 15' 6"
Displacement 23+ tonnes (est from surveyor)

Twin Cummins 555's

1950 rpm 8.8 knots 1.09 nmpg (us gallons)
1800 rpm 7.9 knots 1.35 nmpg (us) 1.62 kmpg (imperial)

800 us gal, 880 - 1000 nmi range

Measured from long runs, tank sight glasses, fill-ups + so pretty accurate.
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Old 03-09-2016, 12:04 AM   #13
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Quote:
Originally Posted by Jay N View Post
Cummins 6BT5.9 210HP, LWL: 34.7', 31000 lbs, semi-displacement

The following operating hours and ranges are based on continuous running and calibrated fuel flow (FloScan). NM/G and ranges can increase up to 20% assuming 4 hour average daily runs and normal times for warming/cooling.

Really Slow Economy cruise: 1400 rpm, 6.2 kts, S/L 1.06, 59.2% propeller efficiency, 28 hp (13% of ME rating), 1.7 gph, 3.7 nm/g, 172 F coolant temp, 380 F pyro, 1.0 lb turbo boost, 195 operating hours with a range of 1207 miles (90%), 74 dba in pilothouse.

Slow Economy cruise: 1500 rpm, 6.5 kts, S/L 1.11, 58.8% propeller efficiency, 34 hp (16% of ME rating), 2.1 gph, 3.1 nm/g, 172 F coolant temp, 420 F pyro, 1.5 lbs turbo boost, 158 operating hours with a range of 1024 miles (90%), 77 dba in pilothouse.

Fast Economy cruise: 1600 rpm, 6.9 kts, S/L 1.18, 58.6% propeller efficiency, 41 hp (20% of ME rating), 2.5 gph, 2.8 nm/g, 172 F coolant temp, 450 F pyro, 2.0 lbs turbo boost, 132 operating hours with a range of 914 miles (90%), 78 dba in pilothouse.

Slow Fast cruise: 1700 rpm, 7.2 kts, S/L 1.23, 57.5% propeller efficiency, 47 hp (22% of ME rating), 2.9 gph, 2.5 nm/g, 173 F coolant temp, 480 F pyro, 2.5 lbs turbo boost, 114 operating hours with a range of 822 miles (90%), 77 dba in pilothouse.

Fast cruise: 1800 rpm, 7.5 kts, S/L 1.28, 56.6% propeller efficiency, 55 hp (26% of ME rating), 3.5 gph, 2.1 nm/g, 175 F coolant temp, 510 F pyro, 3.3 lbs turbo boost, 95 operating hours with a range of 709 miles (90%), 74 dba in pilothouse.


Jay nice bit of computation reflecting attention to details.

Rough by comparison:
,
27' WL length 10' beam,13,000#(est) 3' draft
-85 hp 4 cyl. Perkins @ 2800 RPM. (In current service-2000 RPM max)
Slow Cruise- 1100 RPM-5.5-5.7 Knot .07-under 1 gallon
Mid Cruise - 1200/1250 RPM- 5.9-6 knot. 1 gallon-1.2 gallon
Normal - 1400/1450 RPM- 6.9-7.2 knot 1.4 gallon
No Max-Self limited to 1400-1450 RPM
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Old 03-09-2016, 12:50 AM   #14
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Ocean Alexander 50 Mk 1, now 60,000lb
Twin John Deere 6068 TFM75 (201HP each)
Fuel capacity: 1240 USG.
Range: adequate

For the first 100 hours engines were operated mostly in range of 50-80% power, as required by JD during break-in. For 718nm the average economy was 0.99 nmpg (US gallons). Thus av speed was 7.2 kn.

For the next 400 hours engines have been operated mostly in the range 35-50% power. Thus 2793nm, av economy 1.47 nmpg. And av speed 7kn. Average speeds include idling at dock, and effects of wind & currents.

Graph shows sea trial info for speed vs fuel burn
Attached Files
File Type: pdf Speed vs fuel.pdf (44.4 KB, 31 views)
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Old 03-09-2016, 01:50 AM   #15
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Small sample size so far but it's interesting to note the smaller boats calculate in gallons per hour and the bigger boats calculate in gallons per mile
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Old 03-09-2016, 07:46 AM   #16
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Abbreviated recap:

800 RPM, 6.7 Kts, 2.2 GPH (total), 2.89 NMPG
1200 RPM, 8.9 Kts, 5.8 GPH (total), 1.48 NMPG
2200 RPM, 19.1 Kts, 26.8 GPH (total), .71 NMPG

Twin Cummins 450C (8.3C) diesels, planing hull, approx. 28000-lbs dry, LWL 43' 10.5".

6.7 Kts @ 800 RPM is approx. 1x SQRT(LWL). 8.3 Kts @ 1200 RPM is slightly under 1.34x SQRT(LWL).


2200 RPM is our normal "fast" cruise; although the hull rides slightly better at 2400 RPM (200 "off the top") economy at that rate decreases to approx. .63 NMPG.

Results are estimates from measured speed runs then compared to Cummins' nominal fuel burn curves.

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Old 03-09-2016, 08:16 AM   #17
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1983 Atlantic 30 with 165hp Volvo TAMD40B. Last trip up and down river 72 hrs run time and 84 gallons of fuel-5.8 to 6.5 knts up stream at 1800rpm and 6.5 to 7.8 knts downstream at 1600rpm-that's including 4 hours of generator (4.4 Westerbek) run time.
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Old 03-09-2016, 09:37 AM   #18
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1936 Nunes Brothers Raised Deck Cruiser. 32'8" LOA, 32' LWL, pure displacement, 9,500 lbs displacement.

2011 Volvo-Penta D2-40 diesel (39.6 hp) with a 2.69:1 gear turning a 20: dia x 13.35" pitch 3 blade prop.

6 knots - 1650 rpm - 0.3 gph - 20 nm/gal
7 knots - 2060 rpm - 0.6 gph - 11.7 nm/gal
8 knots - 2650 rpm - 1.3 gph - 6.15 nm/gal

My wife likes to run at a bit under 5.5 knots where fuel consumption is about 0.2 gph for 27.5 nm/gal. She likes that speed because it is quiet. I prefer to run around 7 knots.

Assuming that I consume 90% of fuel capacity my range at 5.5 knots is around 1,000 nm. At 6 knots is it about 700 nm and at 7 knots about 420 nm. Two five gallon jerry cans of diesel in the lazarette increase my range by around 25%.

Numbers based on measured fuel consumption for 6 and 7 knots and calculated fuel consumption from power curve and engine data for 8 knots.
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Old 03-09-2016, 09:52 AM   #19
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I hope that all the hull speed advocates are paying careful attention to this data.
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Old 03-09-2016, 10:23 AM   #20
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Some of the above data is no doubt accurately measured and some is no doubt wishful thinking. Here is a way to estimate your fuel consumption at displacement speed that will probably be as accurate as anything posted above. Displacement speed is 1.34* sqrt(water line length).


Displacement hull trawlers typically require about 1.5 hp per 1,000 lbs displacement to reach their displacement speed. Semi-displacement trawlers require 2-2.5 hp per 1,000 lbs. The displacement figure was confirmed by plotting the fuel consumption data given in Bebe's book as revised by Leishman. The semi-displacement figures are from my own experience with semi-displacement hulls. They take more fuel because the hull shape is not optimized for low speed.


So take that horsepower and speed and divide the hp by 16 hp per gph. and you will get gph at that speed. The 16 number works pretty good as it is what a Perkins or Lehman will use at 1/4 rated power. And it is what a high output, turbocharged engine will use at 1/10 rated power. A modern John Deere well loaded will probably do a lot better, maybe 18 hp per gph.


Somewhat less accurate is to do the same thing at a sub displacement speed of 1.0*sqrt(LWL). That will result in about half the hp and gph.


David
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