gas mileage question

[tonyjh63]

Hey guys, went out on the lake last week with a full tank, cruised around the lake for 2.5 hours, then went home. Before hitting the lake yesterday, filled up the tank. It took 14.45 gallons. I assume you would figure up GPH in much the same way as MPG, so 14.45gal/2.5hrs = 5.78 gph. Is my assumption correct? And is this good, bad, or average for my setup? I have a 1993 Glastron SSV 195 Elite with 4.3 Mercruiser/Alpha One...Also, the cruising was done with just me and a passenger.
Thanks!

 

[Scott Danforth]

Re: gas mileage question

I usually figure out how many miles I went via the GPS, then figure out how many gallons I burned in that distance. many boats are about 2-3 miles per gallon at cruise. Things like current, wind speed, trim angle, boat speed (planning or pushing a big bow wave) all effect your fuel economy. cheapest cruise speed is about 3000 RPM ish. cheapest idle speed is at idle. worse fuel usage is while not on plane pushing a large bow wave.

However please note that Boating is not a fuel economy type hobby.

 

[riptide09]

Re: gas mileage question

I never look at gas mileage. I try and look at burn rate. How many gallons per hour based on engine RPM and conditions (such a weather, currents, am I pulling a tuber/boarder/skier, etc.). I always start with a full tank and fill her up after each outing. I have gotten pretty good at estimating how much fuel I have used.

My burn rate is roughly this:
2000 RPM 2 Gallons/Hour
2500 RPM 6 Gallons/Hour
3000 RPM 7 Gallons/Hour
3500 RPM 8 Gallons/Hour
4000 RPM 10 Gallons/Hour
4500 RPM 11 Gallons/Hour
5000 RPM 12 Gallons/Hour

 

[frantically relaxing]

Re: gas mileage question

Just my opinion so no offense to anyone intended, but figuring fuel burn on a pleasure boat at GALLONS PER HOUR is completely ridiculous, especially since GPS's to keep track of actual mileage are dirt cheap. I want to know how many MILES I can go on a gallon of gas, I could care less how many HOURS I can go.

THAT said ( ) -- fuel burn in a pleasure boat is highly dependent on boat and RPM speeds. It's common knowledge that *most* boats get their best mileage at around 1100 rpm (displacement speed) and around 3000 rpm (cruise speed). All other ranges tend to burn more fuel per mile, with the most fuel per mile used at WOT.

Supposing the OP boated 2.5 hours at a typical 30 mph cruise speed, that's a 75 mile cruise at approximately the best MPG speed for the boat. Burning 14.45 gallons in that 75 miles comes to a very economical (for a boat) 5.2 miles per gallon. This is assuming of course never stopping, which I'm sure didn't happen. So even if you calculate in a 50% down time during those 2.5 hours, you're still looking at 2.6 mpg, which is:

Just about average.

 

[JoLin]

Re: gas mileage question

Just my opinion so no offense to anyone intended, but figuring fuel burn on a pleasure boat at GALLONS PER HOUR is completely ridiculous, especially since GPS's to keep track of actual mileage are dirt cheap. I want to know how many MILES I can go on a gallon of gas, I could care less how many HOURS I can go.

No offense taken, but... you boat on a lake. MPG might mean something there, but it's less important when the number of miles you travel at a given rpm is affected by wind, waves and current. I'll use nominal mpg (about 1.7 in my case) for planning purposes, but I think in terms of gph.

 

[dingbat]

Re: gas mileage question

Gallons per any unit is a useless figure. Unless your planing a trip, the only figure that really matters at the end of the day is how much it cost you to fill up.

 

[eavega]

Re: gas mileage question

Gallons per Hour is an incredibly pertinent metric, especially noting how even that changes with changing conditions. miles per gallon will vary with wind, wave, current, tide action or even water temperature for a given engine speed. One or more of those can affect your cruise on any given day. Knowing how your boat consumes fuel on a windy or wavy day could mean the difference between a great day on the water or (at best) having to get towed in.

Rgds

Eric

 

[Mischief Managed]

Re: gas mileage question

Hey guys, went out on the lake last week with a full tank, cruised around the lake for 2.5 hours, then went home. Before hitting the lake yesterday, filled up the tank. It took 14.45 gallons. I assume you would figure up GPH in much the same way as MPG, so 14.45gal/2.5hrs = 5.78 gph. Is my assumption correct? And is this good, bad, or average for my setup? I have a 1993 Glastron SSV 195 Elite with 4.3 Mercruiser/Alpha One...Also, the cruising was done with just me and a passenger.
Thanks!

That is a good way to calculate fuel burn, but I would recommend many more data sets. That GPH figure sounds pretty normal for a boat like yours as well. FYI, you can add a GPS chart plotter and fuel flow probe to your boat for a reasonable amount of money. Nice to know where you are and exactly how much fuel you have.

 

[spdracr39]

Re: gas mileage question

Miles per gallon is irrelevant since you rarely travel in a straight line to where you go. If you do watersports there is not possible way to keep up with it accurately. I always know how long the engine has been running and can always accurately estimate my fuel usage. GPH is overall the best way to gauge it. You can always estimate your Mpg if you know your Gph but I have never needed to know that.

 

[blackhawk180]

Re: gas mileage question

I have a mercmonitor that can display a gazillion engine functions on my HDS 7 (I select the ones I want to view). Among others, I choose to view both MPG and GPH as it helps me get my trim dialed in for max fuel economy. It also will display total fuel burned since last reset (accurate to .2 gal), trip avg MPG, total trip distance in miles, etc etc.
I agree that there are many factors that effect fuel consumption but knowing precisely my mpg/gph allows me to dial things to my liking. If I was only interested in going WOT, I guess GPH would be all I'd need.

 

[Outsider]

Re: gas mileage question

If you do watersports there is not possible way to keep up with it accurately.

Does the boat move during water sports? If so, a GPS will calculate miles traveled even if it's in a circle. Either calculation can be valid since both are an 'average', and which is better depends on usage. I know I don't run for 'hours', I run X miles from point A to Point B to Point C, etc. I run offshore most times I go out, and I know that over 6 years I have 'averaged' 2.873 MPG. I now confidently plan 2 MPG for trips, and I can estimate fuel used (even though I have a gauge) to about 2%. I could figure GPH since my GPS keeps track of running time, but I have little use for it. To me, GPH only facilitates tweaking running performance at any given time ...

 

[spdracr39]

Re: gas mileage question

I guess its kinda like " what type of oil to use" everybody has their own method. I prefer Gph. But I will say during watersports there is no way to predict how many miles you are going to travel because you haven't done it yet. I can however predict how many hours I will be doing it and plan for how much fuel I will be using in that time period so for me Mpg is irrelevant.

 

[H20Rat]

Re: gas mileage question

for my use, miles per gallon is a pointless number. I don't really go anywhere, I don't have a set destination.

My normal day outing consists of a quick 50 mph run to get to the dock to pick up passengers. Then off to the sandbar at best cruise speed for an hour or two. By then I need to recharge the stereo battery so I'll pull someone tubing or wakeboarding for awhile, then back to sandbar. If its too busy by then we just float downriver (2.5mph, infinite MPG's!)

Given a roughly typical day like above, I'll burn about 20 gallons in 6-8 hours. (2.5 gph to 3.3 gph) Total miles would be impossible to calculate.

 

[crabby captain john]

Re: gas mileage question

Not sure what my Mpg would be going with the current or against- then there is the wind/waves that have an effect- is the tide moving with or against my line of travel? Trolling or cruising? Mpg is of no value to me, gph and amount of fuel in the tank is all that counts.

 

[rallyart]

Re: gas mileage question

The single best reason not to use MPG is that it is really depressing when all your other references are cars. GPH means you can confuse your brains idiot switch into thinking that it a nautical norm and you are using an acceptable amount of fuel.
Now, you are using an acceptable amount of fuel if you are having fun and have not run out before you get back to dock.

 

[frantically relaxing]

Re: gas mileage question

for my use, miles per gallon is a pointless number. I don't really go anywhere, I don't have a set destination.

Which is my basis for not using gallons per hour. I'm bright enough to convert 5 mpg @ 30 mph to 6 gallons per hour. But I USE my boats much more than I DRIVE my boats. Example: Last time we launched our SkipperLiner was May 2011. Just a quick calculation here, I've burned about 140 gallons of gas- which is 17,920 ounces- since we launched, which was roughly 17,920 hours ago, so our houseboat is using 1 ounce of gas per hour! Hey, beat that mileage!

Gallons per hour and miles per gallon are the same thing when DRIVING the boat, but not when USING the boat. So I'm way more interested in how many miles I went rather than how many hours I spent doing it. Like today. We spent 4-1/2 hours on the lake in the Chaparral, and drove 9 miles (GPS). I know my boat averages 2 miles per gallon, so I'm pretty confident I used about 4-1/2 gallons of gas.

Even though the houseboat didn't move again today, it still "used" an ounce of gas according to MY version of GPH calculation.

So for ME- miles per gallon.

 

[bruceb58]

Re: gas mileage question

The boat in my signature gets 2.6MPG at Lake Tahoe and can get slightly more at sea level in salt water.

I have a fuel flow meter hooked up to my GPS and I read out the actual MPG at any time and trim my boat to get the max MPG.

 

[Mischief Managed]

Re: gas mileage question

The boat in my signature gets 2.6MPG at Lake Tahoe and can get slightly more at sea level in salt water.

I have a fuel flow meter hooked up to my GPS and I read out the actual MPG at any time and trim my boat to get the max MPG.

I have a similarly-sized cuddy, also with a 7.4, and also get roughly 2.6 MPG according to my similar instrumentation. I love the stupendously accurate fuel level gauge that a fuel flow meter provides. I use MPG to judge my best cruise for a given load, but the fuel gauge is the part I use most. I rarely fill my tank. Why carry all that weight when you can carry just what you need plus a little reserve?

 

[Frank Acampora]

Re: gas mileage question



This 14 foot little thing burns 15 gallons per hour at full throttle at 60 MPH. I use it to zip up and down the river for an hour or so and then go home.

I really don't care how many gallons per hour it uses and I don't care how many miles per gallon it gets. Neither is important to me. ALL I really care about is looking at the exposed 18 gallon tank and having enough fuel to get back to the ramp! The really small 10 footer has the tank between my legs and when I see it get low, I head back--I could not even guess at what fuel mileage it gets.

Now, of course, on my larger boats I do have an estimate but I use the rule of threes when cruising and refueling. After using approximately 1/3 of my fuel I either refuel or head back.

The OP was really only interested in whether or not he was achieving what could be considered average fuel mileage for his boat. It sounds like he is doing slightly better tham average.

 

[dingbat]

Re: gas mileage question

Why carry all that weight when you can carry just what you need plus a little reserve?

Because you don't know how much fuel you will "need" until your back at the dock. ***** happens...... and you'll find yourself wishing you had more fuel at the very worst time. Been there, done that.

I try to carry double what I plan on using.