Figuring fuel consumption

[df909]

Hi Guys-

I plan on taking my 20' runabout with a 4.3L 2bbl Alpha 1 out to an island near me. The boat is about 2,800 lbs. and I'd have only me in it with maybe 200 lbs of stuff. It's about 26 miles and the water is fairly mellow in the morning & I'd be making the trip with a group.

My questions is: how can I get a general idea what my fuel consumption is? I know I can fill the tank and go out for a couple of hours, but that's kind of wasting gas. Are there any other idea you know of? Thanks.

 

[Philster]

Re: Figuring fuel consumption

On average, an in-tune four-stroke gasoline engine will burn about 0.4 to 0.45 pounds of fuel per hour for each unit of horsepower. Likewise, a well-maintained two-stroke outboard burns nearly 0.6 to 0.8 pounds of fuel per hour for each unit of horsepower it produces.

Use the idea of 1/3-1/3-1/3. One third of your fuel is needed for the outbound trip, one third for the inbound trip and another third as a backup in case inclement weather or water conditions delay your trip.

Actual numbers can vary by 10-20%. These numbers are based on peak horsepower, which occurs near wide open throttle (WOT). Cruising RPM should boost the range, but for safe measure, use the lower near-WOT rating.

 

[Texasmark]

Re: Figuring fuel consumption

Got time for a test run prior to the trip? Then you will have exact numbers. I think that would be your best bet.....would not want to be caught out short on fuel because I miscalculated.

Mark

 

[MRS]

Re: Figuring fuel consumption

I have taken a couple different boats to Catalina one had a 175 merc.outboard and burned about 6gal.s an hour at a smooth cruising speed water condition fair with a little wind chop. The second was a 24ft. Hallet with a single 540 built motor and merc. outdrive we ran from 55mph to 70mph fastest I have ever got to Catalina used 55gals. to get there and back
Your boat is close to what I have and I hold 19gals. and have run 40 miles running 3/4 throttle on the river. Plus just to have piece of mind take an extra 5 gal. fuel can with you. How big is your fuel tank?

 

[45Auto]

Re: Figuring fuel consumption

A general idea of your fuel consumption would probably be in the 3.5 MPG range. You can go to Boattest.com and look up a boat similar to yours. For example, this 20', 2800 lb, 4.3L Sea Ray gets a best of just over 4 MPG and gets in the high 3's anywhere between 20 and 33 MPH. You should be easily able to do 26 miles on 10 gallons each way.

 

[df909]

Re: Figuring fuel consumption

Wow, thanks for the info guys. Should have mentioned in my original post, but I have a 30 gallon tank. The motor seems to run very well, sounds good and is nice and smooth. I've only had it about one month have just done the yearly maintainence on it. I'll change the plugs on it as well & probably put some nice platinum in. There's no excess exhaust when I run it in and out of the water & the oil looked ok when I changed it.

And Catalina is just the place I'm planning on going. I will bring 2 five gallon gas cans, but I'd rather not stand on my swim step and fuel the boat. I can't imagine what I'd do to the water and those living in it if I dropped a full gas can overboard.

I'm sure there is, but is there a gas station in the marina at Catalina? What do you think the fuel runs pricewise?

 

[QC]

Re: Figuring fuel consumption

I will bring 2 five gallon gas cans,

I'd skip that and just top off in Avalon . . .

 

[MRS]

Re: Figuring fuel consumption

Diesel fuel and gas are available at the fuel dock next to the Casino. Summer hours are 7 am-6 pm daily. Winter hours are 8-10 and 2-4 Monday thru Friday, 8-4 on weekends. Call (310) 510-0046. Beer, ice, soft drinks and snacks are sold at the nearby Casino Dock Cafe (open 7:30-4 weekdays, 7-6 weekends). Have fun....

 

[Jeep Man]

Re: Figuring fuel consumption

Wow, thanks for the info guys. Should have mentioned in my original post, but I have a 30 gallon tank. The motor seems to run very well, sounds good and is nice and smooth. I've only had it about one month have just done the yearly maintainence on it. I'll change the plugs on it as well & probably put some nice platinum in. There's no excess exhaust when I run it in and out of the water & the oil looked ok when I changed it.

And Catalina is just the place I'm planning on going. I will bring 2 five gallon gas cans, but I'd rather not stand on my swim step and fuel the boat. I can't imagine what I'd do to the water and those living in it if I dropped a full gas can overboard.

I'm sure there is, but is there a gas station in the marina at Catalina? What do you think the fuel runs pricewise?

Pick up a SUPER SIPHON. Its cheap (approx. $10) and avoids spillage. You can transfer 5 gallons in about 3 minutes.

 

[df909]

Re: Figuring fuel consumption

Good idea about the siphon. Looking at the chart provided I ought to make it at least there and I'll fill-up in the marina. I'm going to make this a solo run (no wife or kids) and with a group of other boaters just to see how it goes. I'd like to eventually cruise to Catalina and some of the other Channel Islands for some camping or hiking.

Thanks for the input guys & I'll update you when I go.

 

[GeneH]

Re: Figuring fuel consumption

For information on future runs, take a 5 gallon plastic can to the gas station and add a gallon at a time and mark the side with a magic marker. Get a 6 gallon portable tank for your upcoming trip. Run the engine off the 6 gallon tank until it runs out or low and add from your calibrated 5 gallon can. This should give you a pretty accurate idea of how much you actually used on your trip and what to expect on your boat in the future. Good luck!

 

[themaniam1]

Re: Figuring fuel consumption

Take a GPS with you and clear the trip meter. Than simply fill up at Catalina when you get there and do the simple math of miles traveled divided by gallons filled. That way you will find out your fuel consumption and then can calculate any trip. I would not even worry or hassle about taking extra fuel since you can fuel up at the island. I have a 6000 lb cruiser with a 350 mag and get 4 mpg at 35 mph cruise with full fuel, water and gear. You should get that which means you have 120 mile range at least. My 2 cents worth.

 

[df909]

Re: Figuring fuel consumption

I think I'll do the GPS thing when I go to the island and while I'm playing around at the lake. I didn't even think about taking it to the lake when I'm buzzing around. The idea about the gas cans is a good one too, but knowing me and my luck I'd somehow hook up the water inlet to the fuel line rather than my 6-gallon tank.

My wife is too happy to stay home while I go to Catalina alone...and she made sure my life insurance paperwork is up to date. And I wonder why she went to the Jaguar dealership the other day...

 

[QC]

Re: Figuring fuel consumption

I have a 6000 lb cruiser with a 350 mag and get 4 mpg at 35 mph cruise

Please give us some more data on this boat. I am not trying to be a problem here, but most 6000 lb cruisers struggle to get 2.5 at 25 MPH empty, so I am very curious about this. Range is an extremely important topic and I want to make sure we all have good data to work from. Thanks

 

[Snobike Mike]

Re: Figuring fuel consumption

Please give us some more data on this boat. I am not trying to be a problem here, but most 6000 lb cruisers struggle to get 2.5 at 25 MPH empty, so I am very curious about this. Range is an extremely important topic and I want to make sure we all have good data to work from. Thanks

I agree. Something doesn't sound right.

My 4000 pound 21 foot bowrider gets around 4.5 mpg at 30 mph with a 350 so a 6000 pounder with the same engine going faster should have much worse fuel mileage.

 

[Silvertip]

Re: Figuring fuel consumption

The most accurate way to do this is obviously with a fuel flow monitor but since most boats don't have one, you can use the figure 10% of engine horsepower at wide open throttle. Therefore 200 HP will consume about 20 g/hr at wide open throttle and probably 1/2 - 5/8 of that amount at about 2/3 throttle (comfortable cruise). Every boat/engine combination is different due to load, design, wind, water conditions, etc so the numbers can vary.

 

[H20Rat]

Re: Figuring fuel consumption

I agree. Something doesn't sound right.

My 4000 pound 21 foot bowrider gets around 4.5 mpg at 30 mph with a 350 so a 6000 pounder with the same engine going faster should have much worse fuel mileage.

I agree, 4 mpg at 35 mph is about 8.75 gallons per hour. That would give it the exact same efficiency as a 20 foot light bowrider.

Just glancing at boattest, they have a 6400 pound cruiser with a 350 in it, at 35mph it is burning 14 gallons per hour/2.5 MPG.

Now the bayliner 20 foot bowrider with a 220 4.3 liter engine does 8.6 gallons per hour/4 MPG at 35 mph, but it also weighs 2800 pounds.

(both with fuel injected engines also)

 

[Pez Vela]

Re: Figuring fuel consumption

I know I can fill the tank and go out for a couple of hours, but that's kind of wasting gas ... I have a 30 gallon tank.

Really? Your approach to good seamanship is dubious at best, and foolhardy at worst. Running out of fuel is the least of your problems. You should have greater respect for the Catalina Channel and know your own limitations.

 

[Snobike Mike]

Re: Figuring fuel consumption

The most accurate way to do this is obviously with a fuel flow monitor but since most boats don't have one, you can use the figure 10% of engine horsepower at wide open throttle. Therefore 200 HP will consume about 20 g/hr at wide open throttle and probably 1/2 - 5/8 of that amount at about 2/3 throttle (comfortable cruise). Every boat/engine combination is different due to load, design, wind, water conditions, etc so the numbers can vary.

10% at wide open throttle is a big guess too. My boat runs just under 7% of rated hp at WOT.

I agree, get a flow meter and then you will know.

 

[df909]

Re: Figuring fuel consumption

Really? Your approach to good seamanship is dubious at best, and foolhardy at worst. Running out of fuel is the least of your problems. You should have greater respect for the Catalina Channel and know your own limitations.

What does this mean?