Oldav8tor wrote:
Your replies mostly go along with my thinking.... I'm not ambitious enough to go to all the trouble to nail it down to the last tenth of a mpg. As it is, a boat has many drag producing elements as it is that can sometimes be mitigated but not eliminated.
I realize that boating and fuel economy do not go hand in hand..... aircraft tend to use a lot of fuel per hour too, only they do a lot better in the speed department. I have a lot to learn about my Sundowner and plan to experiment with loading, trim and power settings to see what will give me a decent speed and reasonable economy. I'm not a kid who has to be at full throttle all the time.... rather, a prudent sailor who prefers to know his vessel and how to get decent performance from it. For that reason, I appreciate you sharing your knowledge and experience with me.
In the FWIW department, my last two trips this fall showed an interesting contrast in fuel consumption..... The first, a 35 mile trip on the St.Clair and Black Rivers by Port Huron, MI, consumed 11 gallons of fuel. Thirty of the miles were on plane running down and up the St. Clair while 5 were at no-wake speeds on the Black. The St.Clair was pretty smooth (except where the river begins at the foot of Lake Huron) but not glassy. The second trip of 24 miles was on Lake Huron, from Port Sanilac to Lexington and back. Waves were running 1 foot or so and I was on plane at 22-24 mph. Fuel consumed, 10.8 gallons...... Loading in both cases was almost identical. Wind and wave action were the main difference, but it surprised me that it would have that much of a effect. Like I said, I have lots to learn which is part of the fun.
I've done a number of trips over 80 miles each way in my H240. I get a little less than 3mpg (like 2.85 or 2.9) with a good load in the boat. My 5.7L is carbureted, so those with Fuel injection would see about 15% better than that.
The most important thing is to stay at an efficient "cruising speed" which for most is 3000-3500rpm. Next is to "trim up" for the least water drag. Without changing the throttle, you can change the trim for best GPS speed. Generally UP is more efficient, but if your bow starts to bounce up and down then your too high. Or if the rpm jumps up (prop aeration) then your too high. Every boat model is a little different, but your GPS can help fine the most efficient trim.
You could also try your Bimini Up vs Down experiment the same way...leaving the throttle the same on smooth water, see if you can see a GPS speed difference with the top up or down.
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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings
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