Cut Fuel Costs

[Putershark]

OUTDOORS COLUMN
Boaters Can Cut Fuel Costs By Letting Off The Throttle
By FRANK SARGEANT
Published: Apr 23, 2006

The pain at the pump is not limited to vehicle drivers these days. The price of gasoline is also having a major impact on boaters, particularly those who run larger boats and travel offshore regularly.
Some anglers are making fewer trips. Others take along extra buddies to share the cost. Some are even investing in new four-stroke or high-pressure direct-injection (HPDI) two-stroke motors, hoping to amortize the cost with fuel savings that can run up to 40 percent over older carbureted two-strokes.
But some of the simplest ways of cutting fuel costs are free. It's commonly known that reducing rpms reduces fuel use, but most anglers are not aware of how much of an impact cutting back a bit can have.
Because I frequently run fuel-consumption tests for Boating magazine, I'm constantly reminded of the wisdom of a light hand on the throttle.
A 240 Everglades center console I tested recently at New Smyrna is a case in point. This 4,000-pound boat powered by twin 150-horse four-stroke Hondas used 29.5 gallons an hour at wide-open throttle of 6,000 rpms and a speed of 44.1 mph, for an average mpg of just 1.5.
But at 4,500 rpms and a speed of 28.3 mph, the fuel use improved dramatically to 2.2 mpg - a 47 percent improvement! Yes, you get there a little slower, but the leap in economy is well worth it - and many days offshore, it's far more comfortable to run at 28 mph than at 44 in any case.
The impact on the wallet is significant. Say you ran 50 miles offshore, and then 50 miles back - 100 miles, divided by 1.5 means you'd use 66.7 gallons at full throttle. At 4,500 rpms, you'd use 45.5 gallons. You'd burn 21.2 gallons less, and save a minimum of $60 at current gas station prices, even more if you were to fuel up at a marina.
Other outboards produce nearly identical savings at reduced rpms. Most hit their best planing economy somewhere between 3,500 and 4,500 rpms.
And, though four-strokes are reportedly grabbing about 60 percent of the new motor sales these days, the HPDI two-strokes are just as fuel-efficient, and most are lighter and provide a much quicker hole-shot or take-off than the four-strokes.
As a general rule of thumb, you can expect all outboards to burn somewhere around a gallon per hour per 10 horsepower at full speed, which is to say a 150 burns 15 gallons an hour, a 200 burns 20 and so on. Yamahas seem to do a little better than this in both their four-stroke and HPDIs, but in general it's a pretty good estimate.
Which also means that the more power you put on your boat, the more fuel you'll use. While twins make sense for offshore use thanks to the redundancy, triples do not. The drag of that third lower unit means you get a lot less speed than you'd expect from the added horsepower, but the fuel cost is enormous. Of course, folks who can afford triple outboard offshore boats probably don't care too much about the fuel cost, in any case, but they might care about the reduced range that results.
One other point, a "get home" tip that also results from fuel use observations; at very low speeds, four-stroke outboards almost go into hibernation regarding fuel use. Should you find yourself far offshore with possibly inadequate fuel to get home, you can greatly improve your chances of not having to row the last several miles by heading back at trolling speed. At 1,000 rpms, the twin 150 Hondas mentioned above got 3.7 mpg and pushed the boat at 4.4 mph. A nice plus is that you might catch a kingfish or a grouper on the long, slow trip home.
The alternative, of course, is to call one of the commercial rescue services to bring you some fuel. A few years back I was out with some friends about five miles off Miami when they ran out of gas - faulty fuel gauge, was the excuse.
The rescue service was very happy to bring us five gallons to get home. The price? One hundred and fifty dollars.

Talk about pain at the pump.

[Genelie]

That make so much sence. I burned 7.8 gallons on a 38 mile trip. going soft on the throttle. the next trip was only 12-15 mile trip and burned 3.9 gallons. But I was hot doggin it.

[paginnett]

Check out boattest.com. You have to register. There are a few tests of Triumphs with power/mpg curves. For most four stroke outboards the sweet spot is about 4000 rpms, but it varies with each motor and hull design. The difference in miles per gallon is staggering. One interesting dynamic is that sterndrives tend to be a little more fuel efficient at the high end, but then who wants to be seen in a stern drive? I noticed a big difference on Lake Trinity in No. Cal last weekend. I shot the length of the lake at full throttle, boy that sucks the gas. At about 4000 rpm the gas gauge hardly moved on the return trip. Also, mpg really suffers when your plowing just below planing speed. So those choppy days when you trim the bow up and plow cost a lot fuel.

[MolarBoater]

Yep, @ 4-4.2k rpm probably best with WTO for prop testing only! Plus your motor will last longer.
For those whom like to troll, slow trolling will conserve much better or below 6knts. Fast trolling for wahoo etc, 8+ keeps you off plane and sucks the gas. That being said, I will intemittantly fast troll between reef zones but slow troll most of the time.