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Old 03-09-2016, 10:33 AM   #21
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Nice post David,
I think most just use the hour meter and the #of gallons that goes into the tanks. That of course includes all kinds of running that is not cruise speed and load.

Murray,
I usta cruise my 3HM 35F Yanmar at 2750rpm. I liked it and the Yanmar did too.

Willy is only of average or slightly less than average for efficiency of a FD boat.
1gph
Tad over 6mpg at 6.15 knots.
17,000lbs, 30' OA - 27.5' WLL X 10'6" beam X 3.5' draft.
3000rpm WOT (rated) and 2300 cruise.
2.57-1 BW VD gear w 18 X 13" prop.
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Old 03-09-2016, 10:37 AM   #22
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Quote:
Originally Posted by djmarchand View Post
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.
A shockingly effective experiment to illustrate this is to gather some water in a bucket from alongside your semi-displacement vessel while underway, then do the same from directly behind your swimstep.

Dipping the bucket directly aft is like dipping it in a still pond (boat is "dragging" huge amounts of water the same speed of the boat) while doing it alongside might just rip your arm off (boat is moving "through" that water).
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Old 03-09-2016, 11:09 AM   #23
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Slow-planing V hull, 25'7" LOA, 23'4" LWL, 11,000 lb loaded.
Calculated hull speed: 6.46 knots
Single Volvo KAD44P diesel (260hp), duo-prop stern drive.
Diesel capacity 110 gallons.
Yamaha high-thrust kicker (9.9hp), gas capacity 10 gallons.

Fuel usage measured at every fillup over 6,500 engine hours.
Distance traveled from GPS trip log used to calculate nmpg
- very consistent, assuming effect of current averages out.

At 6.0 knots and 1350 RPM, 4.0-4.5 nmpg, calculated gph = 1.33-1.5

At 17.5 knots and 3200 RPM, 1.75 nmpg, calculated gph = 10.0
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Old 03-09-2016, 11:33 AM   #24
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1.50 GPH 7.5 MPH 2250 RPM Volvo TMD 31 A (100 HP) and NL 5 KW Generator
Fuel capacity 280 gallons 1200 mile range with reserve.
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Old 03-09-2016, 11:39 AM   #25
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HiDHo thanks for the (100hp) as those letters TAMD ect ect mean nothing to us not familar w Volvos.
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Old 03-09-2016, 12:04 PM   #26
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Not terribly apropos to this discussion but for a point of comparison...

Sailboat:
LOA: 40.5'
LWL: 30.5'
Displacement: ~22,000 lbs loaded
Yanmar 56hp 4JH4E engine with Autoprop
6 knots: .75 gph
7 knots: 1 gph
Calculated.

Over the past 6 years total fuel consumption has been 1 gph including the use of diesel furnace and time spent motor sailing.
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Old 03-09-2016, 12:09 PM   #27
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TMD probable turbo motor diesel in Swedish.
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Old 03-09-2016, 12:41 PM   #28
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Quote:
Originally Posted by djmarchand View Post
Displacement speed is 1.34* sqrt(water line length).

Semi-displacement trawlers require 2-2.5 hp per 1,000 lbs.

So take that horsepower and speed and divide the hp by 16 hp per gph. and you will get gph at that speed.

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.

Good post.

FWIW, I talked myself into always interpreting 1.34 x SQRT(LWL) as a theoretical "maximum" displacement speed. As opposed to a mandatory or target speed.

In our case, I think an estimated 2.89 NMPG @ 1.34etc versus an estimated 1.46 NMPG at 1.00etc is a useful illustration.

Given that I only have the manufacturer's fuel flow curves to work with, I can only estimate... but at least long-term usage suggests their nominal curves are in the ballpark on our boat.

If I understand your semi-displacement formula correctly, our 28000-lbs * 2.5 = 70 and 70/16 says 4.375 GPH at our 1200 RPM 1.34etc speed. (Assuming that somewhat works for planing hulls, too.) I'd be happy to learn our burn rate is closer to 4.375 GPH (~2.03 NMPG) at that speed of 8.9 kts, versus our current estimate of 5.8.

I'm installing new digital fuel gauges in a few weeks, so hope use those to tweak my current estimates. Still won't be Flowscans, but incrementally better than what I've got for measurement now.

-Chris
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Old 03-09-2016, 02:57 PM   #29
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dhays,
Ten foot overhang? Wow. Is she an old boat? S/L ratio does wonders. Your 40' boat weighing several tons more than my 30' boat and burning a quart less fuel at the same speed. Your WLL is only 3' longer than mine but it sure delivers. This is a good lesson for all re SLR ... Speed Length Ratio.
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Old 03-09-2016, 03:42 PM   #30
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Quote:
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dhays,
Ten foot overhang? Wow. Is she an old boat? S/L ratio does wonders. Your 40' boat weighing several tons more than my 30' boat and burning a quart less fuel at the same speed. Your WLL is only 3' longer than mine but it sure delivers. This is a good lesson for all re SLR ... Speed Length Ratio.

My bad. A typo. LWL is 36.5'

Sorry. Too late to edit the post as well.
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Old 03-09-2016, 06:30 PM   #31
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Here's a performance chart on our Manatee from a couple years ago. Flowscan readings were identical to the original Volvo 90 at 1500 and 2500 and nearly the same throughout the RPM range with a slightly repitched prop. Sweet spot for vibration was 2200, but fuel consumption sweet spot may be 2600, which, at least according to the flowscan, was no perceivable increase over 2500.
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Old 03-09-2016, 06:38 PM   #32
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This has been an extremely interesting thread for me since I am just finishing up installing a Maretron FFM-100 Fuel Management system. I won't go in to the cost ($$$$$) but below are the data that I expect to see. The FFM-100 displays its data on a DSM -150 that is completely programable. Once the sensors are installed in the fuel lines (2 for each engine) and the sensor are in each fuel tank, the system is automatic. No calibration required after the set up.

In the past I've had 2 FloScans and try as I did, I could never get them close to what I was seeing at the pump.

Panbo: The Marine Electronics Hub: Maretron FFM100 fuel flow monitor test (part 1), as good as it gets?
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Old 03-09-2016, 06:43 PM   #33
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Yes, very interesting to see all the various numbers, thanks to all who are sharing what is their fuel usage.
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Old 03-09-2016, 07:23 PM   #34
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Quote:
Originally Posted by Codger2 View Post
...
In the past I've had 2 FloScans and try as I did, I could never get them close to what I was seeing at the pump.
...[/URL]
Never bothered to calibrate my FloScans. I mentally adjust readings multiplying by 70%, if being conservative, based on experience.
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Old 03-09-2016, 08:30 PM   #35
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The previous owner of our boat installed the floscan system, but our only gauge is a sight tube. The figures in the graph above are pretty much what we found at the pump, plus or minus 5 percent, and wind/weather would surely have made that much difference. Unit calibrated by Scott Marine Power.
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Old 03-09-2016, 08:41 PM   #36
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I manage about 1.5 to 2.0 gallons of diesel an hour operating around six or so knots. I'm too lazy now to repeat details which I've already posted here several times.
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Old 03-09-2016, 08:54 PM   #37
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Quote:
Originally Posted by Codger2 View Post
This has been an extremely interesting thread for me since I am just finishing up installing a Maretron FFM-100 Fuel Management system. I won't go in to the cost ($$$$$) but below are the data that I expect to see. The FFM-100 displays its data on a DSM -150 that is completely programable. Once the sensors are installed in the fuel lines (2 for each engine) and the sensor are in each fuel tank, the system is automatic. No calibration required after the set up.

In the past I've had 2 FloScans and try as I did, I could never get them close to what I was seeing at the pump.

Panbo: The Marine Electronics Hub: Maretron FFM100 fuel flow monitor test (part 1), as good as it gets?
I'm very interested in your experiences with the Maretron system. I'd like to gradually upgrade my boat to use N2K and the Maretron sensors and software. Fuel, engine gauges, water tanks, etc will all be things I want to add over time.

Richard
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Old 03-09-2016, 09:00 PM   #38
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measured by fuel in the tank and hour meter.

Various rpms, between 1450 and 1800. Over 15 seasons.

1.5 gph producing 7.5knots on average.

20000 lb displacement

35' LWL, 10.5' beam
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Old 03-09-2016, 10:04 PM   #39
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Another reference point for a sailboat. Allied Princess 36 full keel sailboat. 36' LOA, 27.5' LWL, 4.5' draft, 11' beam, 15,500 lbs displacement. I normally motor at 6 knots. My 20 year average fuel consumption is 0.46 gph or 13 nm/gal.
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Old 03-09-2016, 10:18 PM   #40
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[QUOTE=manyboats;Quote [Willy is only of average or slightly less than average for efficiency of a FD boat.
17,000lbs, 30' OA - 27.5' WLL X 10'6" beam X 3.5' draft.]

Eric, I am going to have to add more ballast!! I thought 13,000# was a bit heavy with a factory weight of 10,000# out of the box. The bigger engine, usual adding of home bound items, and dedicated 1200# of lead ballast is some short of your 17,000# Good to know information as we are close in all the other measurements.

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