Fuel economy

[pugtug613]

On the way home this weekend, I way playing with my speed and checking my fuel economy. It was absolutely flat with little or no wind or currents. I have an R27 with a 180 HP Yanmar. I experienced the best fuel economy at 12 knots. I was getting 6 GPH and 2NMPG. I figured slower was better. At 8 knots I was looking at 4GPH, but only 1.5 NMPG. I assumed it was because the boat is being "pushed" along at 8 knots and at 12 knots, you "sort of" get up on plane. I noticed if I get her up to 10 knots and then play with the trim tabs, it will get up to 12 - 13 knots w/o more throttle. On a long trip, I guess it would be beneficial from a fuel burn status to travel at 12 knots? Is the NMPG more important than the GPH? I come from a sail boat and I NEVER concerned myself with fuel burn. I would go an entire season using 20 gallons of fuel!

 

[walldog]

To get decent economy, you need to get that R27 down to sailboat speeds. 8 knots will burn more fuel in a trip, NMPG is the indicator to use. The best economy for our R27 was at 1600 RPM or 1 GPH and we varied between 5 to 7 knots doing 5 to 7 NMPG. Once we increased to get on the plane, we dropped to about 2 NMPG and was flat from 12 to about 16 knots. WOT gave us around 19 and 1.5 NMPG.

Of course wind and currents play a factor and how much gear you are carrying around also makes a difference. Then there is the condition of your bottom.