Let's talk fuel economy

[oldsub86]

So, how close to boats emulate cars and trucks? How much difference do size, weight and engine size make for fuel economy in a boat?

If I find a 18 to 22 foot aluminum boat with a 4 cylinder I/O, am I going to see much better fuel economy than I will with a similar sized boat made of glass with a V8 I/O?

I assume I will take some loss on performance but I can accept that. I don't plan to pull skiers and I don't need 50 mph speed.

Tell me what your experience would indicate in these circumstances.

Randy

 

[Bt Doctur]

Re: Let's talk fuel economy

1-2 nautical miles/gal

 

[F14CRAZY]

Re: Let's talk fuel economy

There is no "fuel economy" when it comes to boats, only consumption measured in distance/consumption, or maybe time/consumption

I get 3-4 mpg in my Capri. My Kawasaki 650 cc Jet Skis do about the same

 

[Silvertip]

Re: Let's talk fuel economy

Oh no -- the dreaded fuel economy debate. If you have to worry about it don't by a boat. There is no comparison between economy on a boat and economy with a car, truck, airplane, weed wacker, or lawn mower. They all serve very different purposes. A car rarely sees more than 2000 rpm at highway speed while a boat engine is over 3000 rpm most of the time and regularly sees 4000 - 4800 for long periods. Friction caused by water means the boat is dealing with the most resistance nearly all of the time. While cars and trucks have transmissions to get you up to speed, a boat has one gear and it must not only get the boat on plane but it must also prevent lugging the engine at wide open throttle and it must also prevent over reving at wide open throttle. That gear is not the gear in the lower unit but rather the propeller in combination with that gear. Too much pitch and the engine lugs, requires too much throttle opening and fuel economy suffers as does engine life. To little pitch and the engine over revs which can destroy it and while doing so also burns more fuel than necessary. As for boat fuel economy, there are a couple ways to look at it. A bigger engine loafing is a longer lasting engine and only marginally less economical than a small engine working its guts out to maintain any respectable speed. While you may not want a 50 mph boat, you may want to cruise with five or six people and that little engine will struggle to get on plane and you will need to apply more throttle to maintain cruise speed. If you are getting the impression there is no cut and dry answer to your question you'd be right. Generally (and very generally) the smaller engine will provide slightly better economy than a V6 or V8 but that all depends on the boat it's installed in. It boils down to the level of performance you are after and how you look at resale value. The small engine boats are generally entry level boats and people soon realize they want something better so they opt for the V6 or V8. In my view, the V6 is a great compromise between economy, performance and resale.

 

[wca_tim]

Re: Let's talk fuel economy

there are some really good posts that 45auto put a ton of info up in... a search should yield all the information you need. be careful what you ask for...

 

[BWR1953]

Re: Let's talk fuel economy

If you want "real" fuel economy, get an old displacement hull trawler. I recall back in the 90s that there were some getting 20mpg. They're slow boats, like 5-7mph, but they deliver economy.

Other than that... fuel economy is a phantom not to be achieved with "regular" boating. Sailboats anyone?

Anglers often use much less fuel because they make a run, then sit for hours, use electric propulsion or poles to move the boat around. Folks who like to drive all the time, either sightseeing or pulling toys, will use tons of fuel. Literally. LOL

 

[BamaAlum97]

Re: Let's talk fuel economy

If I understand correctly...what you are really wanting to know is does bigger engine/more power = more fuel usage and vice versa. The short answer is yes. But in reality your choices are between poor fuel effciency and worse...

fuel economy on a boat is relative and there are certainly options to make improvements...I opted for a fuel injected (MPI) V6 with the same HP as the carberated V8...better fuel efficiency at the cost of some low end torque...you just have to decide what is most important to you...

 

[180shabah]

Re: Let's talk fuel economy

The bigger part of the equation is the boat, no the engine in it. Hull design and weight will make a huge difference. Two different engines in the same hull will get nearly identical "economy" at any given speed. Two different engines in two different hulls made of two different materials = too many variables.

 

[bekosh]

Re: Let's talk fuel economy

In identical hulls, you won't see a noticable difference between a 4, 6 or 8 cylinder engine. If anything, for the 18-22 ft boat the OP mentioned, the 4 cyl might actually get WORSE economy than the 6 or 8 cyl because it would running harder just to keep on plane.

Where you will see a difference is between fuel injected and carb. Or a lighter shallow V hull vs a heavy deep V.

So if you are looking for fuel economy , a stripped down, flat bottom aluminum boat with a fuel injected engine will get you the most mpg's. And beat the snot out of you in any type of sea.

 

[Mark42]

Re: Let's talk fuel economy

With boats it is not 'fuel economy', its 'fuel consumption'.

My 14' planing hull runabout w/40 hp twin cylinder Evinrude on a long trip at about 3000 rpm yields 7 mpg.

Same long trip in a 16' deep V hull, 85hp Force, yields 5 mpg.

Its all about the design of the boat, the speed, the HP, the size, and the weight. So fuel consumption varies even amongst boats of the same length and hp.

 

[Andy in NY]

Re: Let's talk fuel economy

I dont know what my boat does for consumption, but I have a 14' tri hull with a 50 hp merc, and can take the wife and 3 kids out crusing for a bit, then sand bar, then cruise, lather, rinse and repeat using less than 6 gals. My friend has a 24' bayliner and a chevy 305, and goes cruising for the afternoon and uses about 20-25 gals. my other friend has a newer seadoo 19' with a fuel injected merc sterndrive (about 260 hp) and can easily go through 30 gal in an afternoon with 4-5 people pulling a tube all day.


its all relative.

 

[QC]

Re: Let's talk fuel economy

In identical hulls, you won't see a noticable difference between a 4, 6 or 8 cylinder engine. If anything, for the 18-22 ft boat the OP mentioned, the 4 cyl might actually get WORSE economy than the 6 or 8 cyl because it would running harder just to keep on plane.

I agree not much of a "noticeable" difference . . . However, despite conventional wisdom, test data tends to show that the smaller engine will get better fuel efficiency at cruise speeds.

Another interesting note that I picked up while farting around with a wooden hull. Modern boat building techniques have resulted in next to no weight difference between wood, aluminum and fiberglass construction of the same hull design. Surprised me, but tends to hold up with manufacturer specs.

 

[tashasdaddy]

Re: Let's talk fuel economy

if you have to worry about fuel economy, you do not belong in boating.

 

[Andy in NY]

Re: Let's talk fuel economy

if you have to worry about fuel economy, you do not belong in boating.

I disagree.

My family of 5 lives off a serious budget. Economy IS important to me, and we make boating work within our budget. There is a reason we dont have a 21' boat with twin 350's. there is a reason we fish and frequent the sand bar often.

Our typical outing lasts 5-6 hours, usually an hour or so of tubing, then a few hours on the sand bar, i might go back out to fish while the wife and kids play on the beach, then usually a few laps around the lake before heading home. we do activities like this because we know we cant blow $100 in gas a weekend. I usually make my 6 gal tank last sat and sunday.

Economy can be had with a little forethought.

 

[rrhodes]

Re: Let's talk fuel economy

I measure by Gal per Hour. If we are tubing or running WOT I burn about 11gal per hours. Cruising about 4gal per hour.

 

[SeanMcl]

Re: Let's talk fuel economy

Has anyone mounted a fuel flow meter to try and measure/improve their fuel consumption? Could changing your cruise RPM up or down a few hundred net much of a change in smaller craft?

Doing the ROI numbers, if I spend $150 on a flow meter, and with gas at roughly $3 a gallon, if I can realize a 10% decrease in overall consumption (wild guess), it would take me $1500 in fuel, or 500 gallons burned, or roughly 17 tanks of fuel in my boat to get my money back. That's about 2 years of boating for me, and that might be worth it. Plus, I would love to know how much fuel is REALLY left in the tank.

 

[BWR1953]

Re: Let's talk fuel economy

if you have to worry about fuel economy, you do not belong in boating.

I disagree.

My family of 5 lives off a serious budget. Economy IS important to me, and we make boating work within our budget. There is a reason we dont have a 21' boat with twin 350's. there is a reason we fish and frequent the sand bar often.

Our typical outing lasts 5-6 hours, usually an hour or so of tubing, then a few hours on the sand bar, i might go back out to fish while the wife and kids play on the beach, then usually a few laps around the lake before heading home. we do activities like this because we know we cant blow $100 in gas a weekend. I usually make my 6 gal tank last sat and sunday.

Economy can be had with a little forethought.

I agree with Andy. There were many times when I was able to use less than 6 gallons of gas with my 50hp Mercury for an entire weekend of fishing.

I for one grow weary of hearing that boating has to be expensive. So far this year, I've bought 2 boats, 2 trailers and an outboard and none of it has cost me anything. In fact, I'm money ahead. Boating is not always about the Benjamins. Often, it IS about forethought.

 

[IVAZ]

Re: Let's talk fuel economy

I disagree.

My family of 5 lives off a serious budget. Economy IS important to me, and we make boating work within our budget. There is a reason we dont have a 21' boat with twin 350's. there is a reason we fish and frequent the sand bar often.

Our typical outing lasts 5-6 hours, usually an hour or so of tubing, then a few hours on the sand bar, i might go back out to fish while the wife and kids play on the beach, then usually a few laps around the lake before heading home. we do activities like this because we know we cant blow $100 in gas a weekend. I usually make my 6 gal tank last sat and sunday.

Economy can be had with a little forethought.

What you are describing is not really fuel economy, its called not putting a lot of use on it. If you go out and just fish from it you still cant say it gets good fuel economy. If you buy and sell stuff to get extra cash as BWR1953 does, your still not getting good fuel economy. I do commend you for doing whats necessary to take your family to the lake and only spend what your budget allows. Most people would give it up or go over budget.
I agree with TD, boating is not cheap. If you go and run it all day a few days a week the gas will cost you a decent amount of money. If you keep up with all the service of the boat it will also cost you a good penny. I don't think boating is the most expensive hobby but you certainly have to have some extra coin to do it. The day I start worrying about fuel consumption is the day the boat is gone. I'm not being snotty I'm just saying what others have already said, boats don't drink gas, they chug it.

 

[Andy in NY]

Re: Let's talk fuel economy

IVAZ, I agree with what you are saying. I guess for me, it's not about economy but rather money spent. We use our boat at least once a week, most weeks twice. I a can make 6 gals last sometimes both days. I do what I have to do to keep the boat in good working order without breaking the bank. Yes, this is more expensive than some hobbies and not as expensive as others.

But my original point was that my 4 banger 50 hp merc DOES IN FACT get better economy than a 24 footer with a 350. and as opposed to TD, you can be a boater and concerned about fuel consumption. It is not as black and white as he makes it out to be.

 

[tashasdaddy]

Re: Let's talk fuel economy

B O A T, Break Out Another Thousand.