Normal Fuel Consumption

S

shenanigans

New Member
Mar 30, 2005
9
St. Johns, FL.
Boat Info
1996 Sundancer 270
Engines
7.4 litre Bravo II
High all. Running a 1996 270 Sundancer with 7.4l BravoII setup. Got a quick question. Can anyone give me an idea of typical fuel consumption either in gallons per hour at cruise (my boat cruises just on plane at about 21 knots at 3200 rpm) or in miles per gallon? I believe my boat is eating up fuel at an excessive rate and not sure why. It has had proper service just recently including new ignition components, oil change, the works and the boat only has 200 hours on it currently (153 of them mine and the others the previous owner). Specs say boat is equipped with 100 gallon fuel tank and if the gauge is correct, it appears I ate up about 75 gallons to make a run of approximately 30 miles out and 30 back and maybe 5 miles putting for the fish so 75 gallons seems extremely excessive. The trip out took about 1.5 hours, the trip back the same, and the putting for the fish could only have taken half hour at the most. By my calculations, that puts this boat at roughly 20 gallons per hour at cruise. Boat is equipped with the standard equip including the generator. Prop is in good condition, the trim tabs are adjusted to help the boat run flat, and the bottom paint is pristine. I would understand if I was heading into a strong headwind but today the weather was 5 knots variable winds. Any suggestions?

Please email me and let me know what you think: madmachines@sjgcc.com

Thanks a million all!
 
Fuel Economy

I own a 1991 250 Weekender with 500 hours, which was also called the 270 from 1992 onwards LOA 29'. It has a 330 hp 7.4 (Carb) with a Bravo II and aluminum prop. We estimate we are burning 15 gallons per hour subject to wave action, loaded weight, dirty bottom, prop condition, etc. The dirty bottom has the greatest impact, the prop condition is second, but wave action (height & interval) is a major factor too.

We have not calculated it exactly, but we run at 3,000 rpms and about 25 knots. So it sounds like we are getting similar fuel economy.

Regards,
Kevin
Weekend Mistress
Richmond VA
 
One of the most useful items that you can add to your boat is a fuel transducer and computer. My boat is outboard powered and equipped with a Navman 2100, but you (or your dealer) can install a similar fuel computer on an inboard or I/O powered boat as well.

You would be amazed at how your fuel burn will change due to trim, engine speed, and sea state, so the only real way to know your fuel burn for sure is to install a fuel computer.

Believe me, once you know for sure what your burn rate is at any particular time, the way you drive your boat will completely change.

Looks for fuel computers here:
http://www.byownerelectronics.com/store/home.php?cat=381

Good luck!
 
Kevin, do you use the "gas remaining" feature of your 2100? On my 2 stroke Yamaha the remaining fuel feature doesn't seem to be accurate. I do lots of idling so I guess the fuel meter is not that accurate at idle. Just wondering if you use that feautre and if it's accurate.
 
yachtjim said:
Kevin, do you use the "gas remaining" feature of your 2100? On my 2 stroke Yamaha the remaining fuel feature doesn't seem to be accurate. I do lots of idling so I guess the fuel meter is not that accurate at idle. Just wondering if you use that feautre and if it's accurate.
Click to expand...

I do, and I use the 'alarm' feature to let me know when I need to fill-up too!
My main tank is 127 gallons so I set my alarm for 20 gallons. That gives me about an hour-and-a-half of cruise time to finish what I'm doing and make my way to my favorite fuel dock. :wink:

The Navman 2100 has the ability to change the calibration for accuracy, but I haven't seen the need with my motor. My 2100 has worked fine for me right out of the box.

I have heard of folks with four stroke motors who have changed the sampling rate of the device due to the lower flow of these motors when trolling. Instructions on how to change the sampling rate for these motors was included in the addendum that came with my manual.

One last item... For the transducer to work properly, it has to be oriented properly (vertically), with the inlet on the bottom and the fuel outlet to the motor, at the top as seen in this photo.

Image-0EC302F8F14A11D8.jpg


Failure to orient the transducer properly will result in erratic results.

My fuel computer is one of the most used items I have on my helm. 8)
 
Here is an old wise tale that seems to be a reasonable estimate of (state) miles per gallon.

This assumes you plane out, trim up, run at reasonable a speed, not plow all day and not going wide open, not in a storm and are using gas, not diesel.

Take 12,000 (10,200 if nautical miles) divided by your boats weight in pounds (boat + supplies + gas/water + crew) just estimate all this. This is +/- about 10% of what you should get for your MPG.

One engine, two engines, small or big boat don’t matter.
 
Your boat = 6,500 lbs

Gasoline weighs in at about 8 pounds per gallon

Estimate of fuel (100 gallons full, refill at 30 gallons = 65 average * 8 lbs per gallon = 520 lbs of fule.

Water / Holding tank. I’ll assume 25 gallons of water and 5 in the holding take = 30 gallons * 8 lbs per gallon = 240 lb of water.

Gear/supplies are difficult to estimate but in general I find people under estimate. Take every thing you have and I’m going to say add another 600 lbs.

Crew I’m going to assume 4 people at 200 lbs each = 800 lbs of crew.

Total would be 6,500(boat) +520(fuel) + 240(water) + 600 (gear) + 800 (Crew) = 8660 lbs.

12000/8660 = 1.38MPG.

You put on 65 miles and used 75 gallons or .86MPG.

Yes, this does sound high.

However you said you were going 21 knots for one and one half hours. In this time you should have went 36.225 miles each way. One knot = 1.15 state mile/hour.

So lets do this again but assume you went 36.225 miles each way and trolled for 6 miles.

You would have gone 78.45 miles and used 75 gallons of fuel. This would put you at 1.046 MPG. Still on the low end but not way low.

You could have topped it off more the second time and plowing during the 5 or 6 miles does eat more fuel per mile.

Keep going, fill up a few more times, and let us know how your gas mileage progresses.
 
Presentationrentals said:
Gasoline weighs in at about 8 pounds per gallon
Click to expand...

Actually, gasoline is about 6.5 pounds per gallon.
Water is 8.35 pounds per freshwater gallon.
A minor point to be sure, but if you have large tankage, it could add up. :wink:
 
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