scoutabout
Lieutenant Commander
- Joined
- Oct 14, 2006
- Messages
- 1,568
I have never been overly concerned about fuel burn. We boat mostly on inland lakes every few weekends and spend another two weeks on vacation at the lake. Sure, the cost to fill a 30 gallon tank at our local marina hurts a bit but I probably don't burn more than a 200 gallons a summer.
Occasionally we drop the boat in Georgian Bay for a longer run out from Parry Sound to my step-father's place. I thought I would use this opportunity to try and get some more accurate numbers. What I discovered doesn't really seem possible in light of what I read here about how inefficient boats generally are. So I thought I'd lay out the numbers and let you folks critique either my approach, my math, or both.
A word about the engine. When I was doing my research before buying the Scout, I talked to several Yamaha techs. One of them said that the 90 hp is actually a 100 but the company made a decision at some point to rebadge to 90, discontinuing the "100 hp" line. Aparently this was to help owners qualify for lower insurance rates and was ok as the power ratings for marine engines are allowed to be within 10% of what's on the cowl. I don't know how true any of this is - but if anything, would argue worse worse mileage, not better if the thing actually was putting out a true 100 hp.
Without further ado.
The boat: 17 foot 2004 Scout Dorado with a carbed 90 hp Yamaha 4 stroker (just turned over 200 hours). In terms of weight - the boat (1100 pounds), motor (394 pounds), gas (200), gear (50) and 3 family members (400) - the whole works then tips the scales a just over 2000 pounds (yes, a light hull).
On the way to the launch ramp I filled up the boat at a roadside station then observed the following on the water.
Total distance travelled: 40 miles
Elapsed time on hour meter: 2 hours
Indicated speed: 20-23 mph
Indicated RPMs: 3600 rpm
It was a constant run to the island and back 20 miles each way. Conditions were relatively calm, with little wind. After pulling the boat out of the water at the end of the day I stopped at the same gas station on the way back and topped up the tank, taking on 17.5 litres (4.62 US gallons) of fuel.
So, using higher math, can I assume the following:
Fuel burn at 20 mph: 2.31 gph
Fuel economomy at 20 mph: 8.65 miles per gallon
Seems a bit too good, no? I should not that this is minimum planing cruise speed for us. Really, I do closer to 30 but wanted to do the first run as economically as possible before choosing runs at 30, then 35, then 40 respectively.
Insights and comments appreciated.
Occasionally we drop the boat in Georgian Bay for a longer run out from Parry Sound to my step-father's place. I thought I would use this opportunity to try and get some more accurate numbers. What I discovered doesn't really seem possible in light of what I read here about how inefficient boats generally are. So I thought I'd lay out the numbers and let you folks critique either my approach, my math, or both.
A word about the engine. When I was doing my research before buying the Scout, I talked to several Yamaha techs. One of them said that the 90 hp is actually a 100 but the company made a decision at some point to rebadge to 90, discontinuing the "100 hp" line. Aparently this was to help owners qualify for lower insurance rates and was ok as the power ratings for marine engines are allowed to be within 10% of what's on the cowl. I don't know how true any of this is - but if anything, would argue worse worse mileage, not better if the thing actually was putting out a true 100 hp.
Without further ado.
The boat: 17 foot 2004 Scout Dorado with a carbed 90 hp Yamaha 4 stroker (just turned over 200 hours). In terms of weight - the boat (1100 pounds), motor (394 pounds), gas (200), gear (50) and 3 family members (400) - the whole works then tips the scales a just over 2000 pounds (yes, a light hull).
On the way to the launch ramp I filled up the boat at a roadside station then observed the following on the water.
Total distance travelled: 40 miles
Elapsed time on hour meter: 2 hours
Indicated speed: 20-23 mph
Indicated RPMs: 3600 rpm
It was a constant run to the island and back 20 miles each way. Conditions were relatively calm, with little wind. After pulling the boat out of the water at the end of the day I stopped at the same gas station on the way back and topped up the tank, taking on 17.5 litres (4.62 US gallons) of fuel.
So, using higher math, can I assume the following:
Fuel burn at 20 mph: 2.31 gph
Fuel economomy at 20 mph: 8.65 miles per gallon
Seems a bit too good, no? I should not that this is minimum planing cruise speed for us. Really, I do closer to 30 but wanted to do the first run as economically as possible before choosing runs at 30, then 35, then 40 respectively.
Insights and comments appreciated.
