fuel range-gctid810640

[Tony3055]

Hello, new to this site. I am putting in a 3055 near Dubuque and taking the boat all the way down to the gulf with a couple of friends.

I see there is about a 250 mile stretch between marinas just south of St Louis.

What is my range with twin 350's if I take easy, lets say 10knots with the current?

Thank you for your help. Tony

[yachtman]

At 250 you will be burning fumes if you can even get close.. . At 10 mph you will be burning more gas better speed will be around 6 or 7. At 8mph I start burning excess fuel. I have 32 ft twin. I can go 200 miles but im empty and that is if weather and current conditions are ideal

[dmcb]

Listen up on the 10 mph. You likely would get better mileage on plane.

You just push a lot of water at 10 mph. Go hull speed on one engine but 250 is a long ways on your tank.

Best test it before you leave. You can carry extra fuel.

Doug

[Old_Man_With_A_Boat]

I agree with Doug. You can carry extra fuel with you. If you know what your fuel flow rate is per hour at the speed that you would like to travel. Then you should be able to tell if you would have enough fuel. I have not been on a big river like the one that you are going to be on, but I would think you would gain some free speed with the current pushing you along.

[bkc914]

hi tony,

ive made the trip 3 times, if interested we can get together on the phone. maybe be able kto give you some helpful hints

kevin

[Discovery]

I recently saw 1.47 m/gal with my fully stocked 3055, with family of 4, for a week long trip covering 512 miles. Of note I carry 260 imp gal with me. Main tank, 2 aux 50 gal tanks plumbed below deck, and jerry cans on the bow.

Yes, I travel very heavy on occasion. 3300 rpm @ 27-28 mph seems to be my sweet spot and agree with others that 7-8 mph is more efficient than 10 mph. 7-8 mpg is only marginally more efficient than 28mph with my set up.

Hope this helps with your trip planning,

[Solandri]

The red line in this plot is typical of the MPG a planing boat gets.

[img ]http://www.boattest.com/images-gallery/charts/regal1900-chart.jpg[/img]

Best mileage is at slowest speeds, up until the boat passes hull speed. At that point the MPG will plummet. Hull speed for the boat in the above plot is about 5.8 mph. For a 30 ft boat, hull speed is about 1.34*sqrt(30) = 7.3 mph. As you move through the water, the bow pushes the water ahead of it creating a wave. At or below hull speed, the second (and/or third, fourth, etc) crest of this wave supports the boat. Faster than hull speed, the second crest moves behind the stern and the boat starts to drop into the trough of the bow wave, and you're essentially trying to power your boat "uphill" to make it go faster. This is what causes the mileage to plummet.

[img size=250 ]https://media1.fdncms.com/northcoast/imager/the-length-of-the-yacht-is-important-diagram-by-don-garlick/u/zoom/2172070/sci-hull-speed-graphic.jpg [/img]

Once your speed is fast enough for the boat to start planing, two things happen. First, the hull lifts out of the water so there's a lot less surface area in contact with the water, which reduces friction with the water. Second, you're going fast enough that any one spot in the water is not underneath the boat long enough to start moving down significantly. This reduces the size of the bow wave, and the "uphill" climb is a lot shallower. Both of these substantially reduce the energy required to move the boat forward, and you get the hump in the red MPG graph.

As you go even faster, the wave drag decreases further. But friction drag increases even more, and aerodynamic drag starts to become a factor, causing MPG to drop once again.

So your best MPG is below hull speed. Your second-best MPG is at the peak of the hump when planing. I'm guessing your 200 mile range is based on planing speed? 250 miles should be possible by going below hull speed. But because of your slower speed, wind and currents start to play a bigger role. If your 6 mph over-water speed become 3 mph over-ground speed due to a strong current, that will cut your MPG in half. So you're going to have to be very mindful of the weather and currents the day of your trip.

The other factor that comes into play here is that you have two engines. Generally, 1 prop is more efficient than 2 props (which are more efficient than 3, which are more efficient than 4, etc - that's why the 747 is being phased out in favor of the 777 and A350, and A380 sales are lackluster). So if you're trying to extend range by running below hull speed, you may be able to extend it even more by running on a single engine.

[yachtman]

In my 32 ft I get about 1.2 mpg per gallon at a speed 5 - 6 mph which is my best at 10-12 mph I'm almost double the fuel usage Of bull speed at 15 mph I am almost triple consumption of hull speed.

At 26 mph I drop back down to pretty much the same economy as hull speed. I use fuel faster but I get there faster too.

I can carry 200 gallons with Chevy 350's. At 200 miles I'm pushing it.

[dmcb]

7 or 8 is still way too fast if you seek economy. My 38xx seems to be best at about 6 mph.

Here is a suggestion for economy. Watch your wake. When you see white water you are wasting fuel.

Doug

[Old_Man_With_A_Boat]

Thanks Doug, I like the idea of watching the wake. I will try this next time out on my 3870. At what speed (mph) do you achieve and not get white water?

[Jeffw]

My 305 had a 150+ gal. Fuel tank. What does the OP have?

[dmcb]

"Old Man With A Boat" post=810755 wrote:
Thanks Doug, I like the idea of watching the wake. I will try this next time out on my 3870. At what speed (mph) do you achieve and not get white water?

About 6 mph.

Another thing. When running low speed be sure the trim tabs are all the way up. It will make a difference in speed. I run on one engine most of the time. You don't save half but it allows the one engine to work just a bit harder keeping it at operating temps,

Our typical season is about 550 miles. We anchor the entire season somewhere. Including genny. idle, operating with both engines when necessary, our fuel usage will be about 150 gallons. We do have solar but use the genny daily for hot water for showers and making coffee. Also charging when there is no sun. I have exceeded that fuel usage when weather forced me to use 2 engines on a long haul but I tow a 16.5' boat and never go on plane.

Been doing this with this boat for over 10 years and it is pretty much the same every year. Not exactly of course but it will give you an idea what can happen.

[mister_larry]

In the interest of safety I suggest you install a fuel-flow meter (visit the Floscan folks) buy a couple good sized gas cans, take some readings, invest in accurate charts and do the math.

Heading towards the gulf (going with the current) you should figure out your fuel-consumption rate at various speeds by the time you get to that long stretch south of St.Louis. Fill the appropriate number of gas cans and keep track. IF you are traveling at hull-speed, going with the current you shouldn't get into any trouble even if you have some surprises (traffic, wrong turn, loss of an engine, etc). While in the gulf, run some tests with the boat just popping on plane and record not only the GPH numbers (gallons per hour) but the tach readings and speed.

Going home is where the fun starts. You are going against the current. I would guess this means you MUST take this return trip on plane to maximize your fuel efficiency. Your chart will tell you how many miles it is between fuel stops. Your numbers should reveal your fuel usage at plane. Factor in your speed over ground (loss due to current) and by the time you get close to the south end of that no-fuel stretch you will know how many more gas cans to buy.

When you store the loaded gas cans, balance the load fore-'n-aft so the boat's attitude on the water at plane is what it should be - not pointing uphill.

Have a fun trip and believe me, your best investment WILL be that FloScan.