Fuel Consumption this Summer

[Mark42]

Took a few long trips this summer and kept good record of the gallons used. Using marine charts, I was able to accurately determine the distance traveled and calculated the MPG.

It turns out the 1985 85hp Force on the Bayliner 1600 Capri w/hard top (deep V hull) averaged 5.5 miles per gallon. Of course, there were times of running WOT and just idling. But most of the time was with half to full load of people/cargo and cruising at 25 mph.

I can't tell exactly how many gallons per hour were burned. I didn't keep track of the time very closely, but my best educated guess is about 4 to 5 gallons an hour depending on speed and conditions. I think one trip out by myself in dead calm the boat just sipped the fuel, probably because of the light load and running higher speeds where the motor is in its "sweet spot". I bet it only burned 3 gallons an hour that trip.

I was surprised to see how load affected the fuel consumption. The trips where the boat was loaded to the max just sucked the fuel down. The boat felt heavy, took longer to get on plane, and wouldn't hit high speeds. It was just getting dragged down. Weight really affected the Bayliner more than it does the 14ft MFG with a planing hull. Of course, the MFG can't take as big a load, but when it was loaded, it doesn't feel as sluggish as the Bayliner does. All in all, the Bayliner with the old inefficient Force motor performed well

Not too bad for an old motor and a 24 year old stepped V hull design.

But then again, I did Sea Foam the motor this season!

 

[pmat1]

Re: Fuel Consumption this Summer

I think its time for me to get a bigger boat and motor! they use less gas then my current boat

 

[Mark42]

Re: Fuel Consumption this Summer

I think its time for me to get a bigger boat and motor! they use less gas then my current boat

My Bayliner is a 16ft boat too. Depending on weight, our boats should be similar in fuel use. Actually, I would have expected the 70hp Evinrude to be more advanced than the Force, even though they are the same year. The Force is a really old design, just updated to breakerless ignition.

 

[pmat1]

Re: Fuel Consumption this Summer

i think i run around 10-12 gallons an hour WOT. my boat isnt extremely heavy either, and it has a pretty low draft. Do you have 3 carbs?

 

[Mark42]

Re: Fuel Consumption this Summer

Yeah, it has 3 carbs. Basic rule of thumb says at WOT the average motor consumes 10% of its hp in gallons of gas. So at WOT, my 85hp should be using 8.5 gallons an hour. But I don't run at WOT, probably more like 2/3 to 3/4 throttle most of the time.

So your 70 hp should be using about 7 gallons an hour. So either the motor is propped badly for economy, or all you do it tow tubes, skiers, etc. Towing sucks the fuel down. I guess there could also be motor tuning issues too.

10-12 GPH from a 70hp in a 16 footer sounds like a lot to me.

 

[scutly]

Re: Fuel Consumption this Summer

so my merc 5.7 260 HP uses 26 GPH at WOT???

 

[pmat1]

Re: Fuel Consumption this Summer

i dont think its propped too badly, i know i could go one pitch up, but its not terrible. Hole shot is O.K and top speed is 30. Dont know the revs because my tach froze up last year and didnt get a new one yet. i dont tow tubers or skiers much; my friends dont want to tube with me because i like to whip em around

 

[Mark42]

Re: Fuel Consumption this Summer

so my merc 5.7 260 HP uses 26 GPH at WOT???

Lets assume that you are getting about 2 miles per gallon, which is common for a big V8 in a big boat. At 60 miles per hour, that would be 30 gallons an hour.

 

[werthert]

Re: Fuel Consumption this Summer

Including tip and pumpout, I dropped $100 for just over a quarter tank.

Best money I ever spent.

 

[Jeep Man]

Re: Fuel Consumption this Summer

My 60 hp 4 stroke Bigfoot drinks about 1-1.5 gallons per hr., and that's OK by me.

If, at the end of the day, you have an empty tank and an empty wallet, get another boat.
If you have an empty tank and your wallet's OK, go boating tomorrow.

 

[bekosh]

Re: Fuel Consumption this Summer

My numbers are very consistant. Every season I run about 1100 miles and average 2.4 mpg.

Looks like I'll be over that for this year. I ran 172 miles on the Lake Winnebago system this weekend. That bumped my total for the season so far to 1089 miles with a month and a half to go.

 

[4JawChuck]

Re: Fuel Consumption this Summer

When I swapped out my 1987 50Hp Yamaha for a 2003 90 HP Mercury I thought my fuel consumption would go through the roof, the exact opposite happened. I use approx half the fuel for doing the same speed my 50HP would be WOT for (about 34mph). At WOT on the Merc I get the same fuel consumption but get there in half the time, it definetly does not pay to underpower a boat.

Fuel usage using GPH is misleading since if your getting there in half the time you have just cut your fuel usage in half. Another factor to consider is many boats hull design become more efficient as you go faster, my sponsoned Tuffy is nearly out of the water at 50mph but at 30 mph the sponsons are touching near the rear of the boat and you can feel them dragging the boat.

 

[dingbat]

Re: Fuel Consumption this Summer

In comparison..........

27' Judge Chesapeake w/ Honda 225 hp 4 stroke

Centerline: 26' 4"
Waterline: 23'
Beam: 8' 10"
Draft 17"
Approx. weight: 4500 lbs.

Numbers taken from a Garmin fuel flow sensor:

3800 - 24-25mph - ~7.6gph
4000 - 25-26mph - ~8.0gph
4200 - 27-28mph - ~8.6gph

 

[Mark42]

Re: Fuel Consumption this Summer

In comparison..........

27' Judge Chesapeake w/ Honda 225 hp 4 stroke

Centerline: 26' 4"
Waterline: 23'
Beam: 8' 10"
Draft 17"
Approx. weight: 4500 lbs.

Numbers taken from a Garmin fuel flow sensor:

3800 - 24-25mph - ~7.6gph
4000 - 25-26mph - ~8.0gph
4200 - 27-28mph - ~8.6gph

Wow, that is amazing. That beats the heck out of most inboard powered boats that size.

 

[QC]

Re: Fuel Consumption this Summer

so my merc 5.7 260 HP uses 26 GPH at WOT???

More like 20 . . . That rule of thumb can be off a lot depending on the technology. Latest MPIs could be as low as 15 GPH for 260 HP (Propshaft)

 

[dingbat]

Re: Fuel Consumption this Summer

Fuel usage using GPH is misleading since if your getting there in half the time you have just cut your fuel usage in half.

Are you sure about that? Got any data to back that up?

 

[QC]

Re: Fuel Consumption this Summer

He's making a point that I have also poorly beat to death before. GPH without speed is almost meaningless . . .

 

[4JawChuck]

Re: Fuel Consumption this Summer

Are you sure about that? Got any data to back that up?

Well its the same boat, same fuel tank...I go to the same fishing hole and back in half the time and have a 1/4 tank more fuel than I used to have. Both engines run/ran perfectly. I use the trolling motor to move around once I get there to avoid scaring off the fish.

Thats all the evidence I need.

Unless you want to say Mercury makes a better motor than Yamaha!

If I throttle back the Merc to the same speed I ran the Yamaha 50HP I use about the same fuel. As I mentioned my Tuffy has a sponsoned hull so at higher speeds there is a lot less hull in the water and it flies on the centre vee, basically it becomes a semi-tunnel hull around 50 mph.

Lots of factors affect fuel consumption rates.

 

[dingbat]

Re: Fuel Consumption this Summer

I agree, GPH is meaningless without speed.

 

[Mark42]

Re: Fuel Consumption this Summer

He's making a point that I have also poorly beat to death before. GPH without speed is almost meaningless . . .

Thats why I figure MPG. Not the preferred measure of fuel usage, but after taking a few trips, its easy to calculate how far the boat will go on a full tank. With GPS or charts, a boater can easily determine if a destination is within reach of their on board fuel.