I still have never changed the oil in our trusty dinghy Mack. The logistics of getting it out of the outboard without a spill have eluded me, though I do have a plan. Meanwhile, he started right up this spring, despite the abuse.
I’ve been curious about what range I really have, since we don’t really track distance or hours on the dinghy. I found the approximate fuel consumption per RPM at Tohatsu’s web site.
So, with some simple math and a few observations: 6 gallons / 1.6 GPH = 3.75 hours in the main tank * ~20 mph at max throttle = ~75 miles. With a 2.5 gal spare tank under the seat, we have (2.5/1.6)*20 = 31 miles of backup. Or, about 100 miles of total range.
This, of course, is highly variable. With all four of us in the dinghy, the 20 hp Tohatsu seems to max out at 17 mph, reducing total range to about 90 miles. But, if we only run fast enough to stay on a plane, the rpms and burn rate would be lower. There aren’t fuel burn / rpm curves available for the motor, so I don’t know whether the improvement in efficiency balances out with the slower speed. Typically, the optimum planing speed is just after the boat gets on a plane and the bow drops. Which is about 15 kts. For Mack. Also, we rarely drive the dinghy with everyone in it. Usually is 1-2 people.
It looks like the last time I fueled up was August 2023, so it’s been about 11 months. In that time we only used about 4 gallons of unleaded (we don’t really use the dinghy much). Regardless, I’ll use 60 miles as an effective range – roughly 10 mpg – and start resetting the trip meter on the GPS when I top off the main tank… and then report back!