Fuel efficiency for long-ish trip

[ryno1234]

I'm planning a trip that will be about 80 miles each way (from Sacramento to the Bay Area). I'll be staying overnight and returning the following day.

I'm looking to get the most out of my fuel, within reason.

How do I find an "optimum" (or at least semi close) combination between speed and fuel consumption?

I imagine the goal would be to get on plane and then dial the RPMs back to where we stay on plane but just barely.

Also, I have levelers which can help me get on plane, but also produce drag. Should these be fully in their "up" positions when cruising or is there an advantage to using them to stay on plane even though they produce drag? I'm not familiar with the efficiencies as it relates to the levelers, I only know how to use them to compensate for weight shifts or to get on plane faster.

Boat Specs:
1998 Maxum 2400 SCR ~ 6,000lbs (will have 5 adults on board)
5.0 Mercruiser (carbureted)
4 blade prop
72 gal fuel

 

[Bob_VT]

Whats the minimum speed that the hull will remain planed out? There is a sweet spot that allows your boat to cruise along ...... weather/wind can be a factor.

Have you taken measurements prior to your trip?

A handheld GPS can do a good job while tracking your distance and speed. Work the calulations from that.

 

[dingbat]

My boat is similar size and weight as yours but with a 200 HP carb outboard with 147 gallon fuel capacity.

Been running FlowScan system for 10 years now. When calculating fuel consumption I use 2 mpg which includes the customary 30% fuel reserve.

A 80 mile leg for me would run ~ 2.7 hours (27 kt. @ 4400 rpm) and consume roughly 30 gallons of fuel. If conditions are not good, I could easily burn 45 gallons in the same distance.

 

[tpenfield]

Without having a Flowscan, SmartCraft or a similar 'techy' solution, it is going to be a bit of guess work. 3500 RPM would be a good guess. You want to be enough above your minimum planing speed in order to gain some efficiency, but not too fast as efficiency drops off. (Take a look at some of the boatest.com performance stats for similar sized boats and you will get a general idea of where in the RPM range is most efficient).

Trim tabs do add some drag, so if you need to use then, keep it at a very minimal deflection.

Sea conditions are going to rule the day, and if it is a bit rough, all bets are off. Stay close enough to shore and plan for where you could make a pit stop.

 

[racerone]

Need a bigger tank or a fuel stop to go the 80 miles I think.

 

[Scott Danforth]

your best economy will be at idle
your worst economy will be climbing the hole
your best combination of speed and economy is somewhere between 2500 and 3800 RPM depending on wind, current, speed, load, etc. and will change with the wind

your best economy/speed/load can only be determined with a fuel flow meter as Ted pointed out
a 5.0 carb motor in a 6000 boat will not be getting good fuel economy as that is a lot of boat for such a little motor and it will be working

without knowing your best burn rate, your best bet is to shoot for about 4-6 mph above planing speed and have a refueling plan. being just barely on plane will actually suck more fuel as you are on the edge of the hole

I routinely boat over 120 miles with my 80 gallon tank, however my boat is also much much lighter. I normally tool along at 25mph as I am in the ICW and river and those are the posted speeds

 

[ryno1234]

Thank you everyone for the feedback. I'll look into a fuel flow meter for the future.

 

[JimS123]

My current boats are relatively new and I have access to performance data. I can simply look at the graphs and the info is right there.

If I were you I would do a search for your boat. and see what info is available. At the very least, find a similar size boat with the same engine. If I remember correctly, Boattest.com might be a place to start.

If you get a flow meter, make your own graph.

In any event, 2500-3800 is probably a good guess.

 

[QBhoy]

My thoughts…
Best fuel economy on a boat like this.. is one of two places. Either around 1000-1200 rpm at around 5/6 mph with the bow planted in the water and full displacement mode…or a couple of hundred rpm above minimum planing speed. Say around a typical guess (for that boat) at about 3200/3500rpm in the early to mid 20’s mph.
But I might also add, that if such things bother you…ditch the 4 blade and get a 3 blade.
Avoid stopping and starting or slowing down and then planing again. You’d be amazed at the fuel you’ll use just getting on plane. I’d even take a guess, that just planing that boat…would use as much fuel as it would to cover nearly a mile, if you were at cruising speed. You get the point. Correct trim of the boat will also hugely improve things. Keep the hull high out the water if planing speeds…trim tabs up and not deploying too. Marginal gains make a huge difference over a long distance. Biggest thing of all to improve efficiency, is by far and away…having the boat well propped.