Using the curves, let's have a look at what happens when you pull back on the throttles. Normally, from the top speed of 2300 RPM, you might slow to a cruise speed of 2000 RPM. As mentioned last month, the power used and the fuel burned drop in proportion to nearly the cube of the rpm, so as you can see from curve 3, the power drops from 1,040 SHP to 684 SHP-(2,000/2,300) x (2,000/2,300) x (2,000/2,300) x 1,040 = 684), a reduction of 34 percent. Using curve 5, we see the fuel burned drops a similar proportion, from 60 gph to just under 40 gph, per engine. If you drop back to 1800 instead of 2000 rpm, the savings is even more, with power going to 499 SHP, a reduction of 52 percent, and the fuel rate dropping to 29 gph (visit www.yachtingmagazine.com for more fuel-saving tips).