Fuel use?

[Boomyal]

Can any one post a range of gph fuel use for a small block V-8 I/O in a 20 ish foot midweight boat?

I assume someone has a flow meter on such a set up. It would be good to have idle, pre-plane load, and several rpm choices up to WOT. Also any differences with boat loaded vs unloaded.

 

[tommays]

Re: Fuel use?

Boattest.com has a huge amount of tests with all the motor sizes on different hulls and a sheet with fuel burns from idle to WOT


Tommays

 

[BrianS.]

Re: Fuel use?

They want to charge me $8.00 to see the test on my boat.

 

[QC]

Re: Fuel use?

FInd a similar boat to yours Brian, weight and power. Compare a few as they can differ.

Boomer add around 15% for carbed vs. MPI.

Yes loaded will make a negative difference. Basically loaded it is a bigger boat . . . lower in the agua.

Best rule of thumb I can suggest is that you will average around 3.5 MPG with almost all 20 - 22 footer I/Os. Bigger or faster less, some MPI boats will reach 4 that run around 3000 - 3500 all of the time with very little WOT op and fewer jumps onto plane. A lot of skiing etc, you could see down to 2.5 . . .

 

[Silvertip]

Re: Fuel use?

Gallons/hour is a far more effective measure of fuel consumption in a boat. Install a Navman 2100 for less than $125 and you'll have amount of fuel remaining, fuel flow in gallons/hour or liters/hour, and total fuel consumed.

 

[Boomyal]

Re: Fuel use?

Gallons/hour is a far more effective measure of fuel consumption in a boat. Install a Navman 2100 for less than $125 and you'll have amount of fuel remaining, fuel flow in gallons/hour or liters/hour, and total fuel consumed.

Was going to do that Silvertip. But the minimum stated flow registry is 1.4 gph. I called Navman and they said "Yup, that's the way it is and we have no plans to change it." Sounds like they don't care whether they sell them or who they fool, when they do.

I'm sure that V8 gph at or near idle is probably around 1/2 gph and WOT is no where near the 32 gph that the guage shows for a 150-300hp boat.

 

[QC]

Re: Fuel use?

GPH is the only measure of consumption, it does not, however, give you any usable information on the water if you do not also know your speed . . . I stand by MPG as the ultimate piece of information.

Please someone enlighten me as to what you gain from knowing simply the flow? I am serious, maybe I am missing something, but without speed it only tells me when I am going to run out of fuel, not where . . .

 

[Dunaruna]

Re: Fuel use?

[colour=blue]Navman usually advertise their fuel computer as an 'option' to compliment a GPS unit, but point taken, Q.

As a stand alone unit, it's an accurate fuel gauge only.

 

[Boomyal]

Re: Fuel use?

GPH is the only measure of consumption, it does not, however, give you any usable information on the water if you do not also know your speed . . . I stand by MPG as the ultimate piece of information.

Please someone enlighten me as to what you gain from knowing simply the flow? I am serious, maybe I am missing something, but without speed it only tells me when I am going to run out of fuel, not where . . .

QC, I have an odd shaped tank. It's about 27 x 42 long by 7 1/4" deep. The side walls are 4" high with the bottom, tapering in a Vee down to the 7 1/4" depth. IOW, the bottom conforms to the shape of the hull that it virtually sits on under the floor boards.

I have two issues. By the time that the gas gets down to the 1/2 way mark there is only about 1/4-1/3 of the gas left in the tank as the volume decreases geometrically in the bottom half of the tank.

The other issue is that I cannot find a semnding that has the same degree of arc swing as the OEM sending unit. The OEM swung about 75 deg, all of the replacements swing about 95 deg. This makes it impossible to get any usable info from the guage regardless of how I bend the float arm.

A flow meter will not only give me gallons per hour, which would be nice to find the engines sweet spot with 5.5$ and 6$/gal gas like I had to pay at Shasta last week. The flow meters have resetable fuel used features which would act a very effective gas guage.

 

[QC]

Re: Fuel use?

That's why I asked, Boomer, thanks. The fuel gauge feature had not occurred. I have a similar issue with saddle tanks that taper and they also read relatively higher than they are toward the bottom of the tank . . . :|

I am pretty much an efficiency and specs freak. As far as finding the sweet spot is concerned I would still suggest that you look at the data on boatest.com. I have stared at specs there and mainly on trailerboats for over 20 years. Until recently I had never seen an I/O package that wasn't the most fuel efficient around 3000 - 3500 RPM. This is not necessarily where the engine would be most efficient on it's own, but corresponds more to where the hulls are most efficient. Recently, as boat speeds have increased (higher power more common), some combos are starting to see their best efficiency around 2500. Again this points more to hull efficiency than engine efficiency as the higher speed boats swing bigger wheels and are at the slower, more efficient speed at lower RPM.

I am very curious as to where you find your sweet spot. Gotta keep my spec database up to date . . . 8)

 

[bjcsc]

Re: Fuel use?

GPH is the only measure of consumption, it does not, however, give you any usable information on the water if you do not also know your speed . . . I stand by MPG as the ultimate piece of information.

Please someone enlighten me as to what you gain from knowing simply the flow? I am serious, maybe I am missing something, but without speed it only tells me when I am going to run out of fuel, not where . . .

Most GPH gauges give you more information than just the flow rate. They almost all tell you total fuel consumed.

The Floscan 20B measures flow beginning at 0.3GPH...

 

[Silvertip]

Re: Fuel use?

Boomyal, The Navman 2100 flow rate is as low as 0.4 g/hr, not 1.4. As for the value of g/hr vs mpg there is no comparison. g/hr using a flow meter is accurate and instantaneous and continually updates fuel used (trip and total), fuel remaining, and current flow rate. Miles per gallon without a flow monitor can only be calculated after the fact. You travel so far and pour in so much gas. Divide miles by gallons and you get miles per gallon. Not of very much value except when discussing fuel economy with a buddy that says he gets 3.5 mpg. The airline industry also uses g/hr for accuracy purposes. I installed the flow monitor for the simple reason my gauge is very inaccurate due to a long, wide, shallow tank. That and I want to know the best cruise rpm for best flow rate. I travel long distances and there is only one fuel stop. I need to know where I stand at any given time and the flow monitor does that.

 

[QC]

Re: Fuel use?

Silvertip,

My point was that if you do not have an idea of your MPG you cannot calculate range. I noted that I was missing the value of a flow meter for use as an accurate fuel gauge, makes sense, got it. But I still submit that If you don't take speed into consideration when you have your flow rate info how do you know whether or not you can make it to the next marina?

Example: The marina is 25 miles away and I am burning 15 gallons an hour, I have 10 gallons remaining With those three pieces of information I cannot confirm that I can make it back . . . I need to know my speed which in turn gives me instantaneous MPG and is the ultimate factor for determining if I am going to need my paddle . . . With the above example if I am going 45 MPH I will make it, because I am achieving 3 MPG. However, if I am only going 30 MPH, I am in big trouble . . . In this case my boasting on the dock of 3 MPG vs. 2 MPG has become extremely significant.

 

[Silvertip]

Re: Fuel use?

Huh? I have a speedometer and GPS so I know how fast I "can" go and what the maximum flow rate for the engine is. Obviously I can also run slower than WOT. So, knowing what my flow rate is and fuel remaining I know exactly how far I can go at any given speed. Knowing exactly how much fuel remains on board I can make the very same calculation you did, but with more accuracy. Moreover, I will know 500 feet from the dock if I need to adjust my plans because of wind, waves, load, engine performance, etc., because the flow rate is instantaneous. Lastly, should an engine problem arise where it starts using more fuel (such as a carb issue) the flow rate would indicate that and again, plans can be altered where the problem would likely not be noticed otherwise. The long and short of this is that if using 3 mpg works for you that's fine. All I'm relating is that knowing flow rate can provide much more accurate "real-time" range data.

 

[QC]

Re: Fuel use?

We're agreeing Silvertip. You said MPG was not important. My contention is that with speed (GPS) what you gain with your flow meter is instantaneous MPG. That's all. Semantics discussion mostly. Sorry if I dragged it out.

 

[Silvertip]

Re: Fuel use?

No problem -- thats why its called a forum. d