Took my boat out for the first time! MPG?

[Todesengel]

Hey guys,

I just got a 16ft Invader Vee, with a 85hp Johnson V4. It was overheating when I got it, but it was just a clogged pee hole. I actually traded one of my salt water reef aquariums for it. Anyway, we got it out on the lake, and I ran 2 tanks of fuel through the boat. It ran great and hit 32.9mph on the GPS. Is this an acceptable speed for this motor?

Now I have a 12 gallon tank and this motor drinks fuel like its going out of style. I went through 3 gallons of fuel going 10miles on the GPS. I don't have a tach, but I cruised prob 3/4 throttle the whole way out there at about 20-25mph. Is that normal fuel consumption for a Johnson V4?

I don't know anything about props, as this is my first boat but one of the blades has a slight bend in it, I don't know if that's a huge deal or not, doesn't look that bad. It seems to be pulling a skier out of the water no problem. How can I find out what type of prop I have, and what are some ways to improve my fuel mileage? Will putting all my ice chests and storage in the front of the boat make a huge difference?

Thanks!

Canyon Lake, Az!

 

[d.boat]

Re: Took my boat out for the first time! MPG?

Beautiful spot!

For what it's worth, your MPG doesn't seem bizarrly bad to me. Outboard engines burn a lot of gas, unfortunately. 3-3.5 mpg. It also seems like you're burning maybe 6 gallons/hour at cruise, about 2/3-3/4 your wide open speed? That's about 30% less than what your wide open GPH at wide open would be expected to be for that engine (see below), which doesn't seem off base to me.

Just to get you in the ball park though...

Generally, engine fuel usage is discussed in gallons per hour (GPH). MPG is an excellent way to look at things, especially if you're trying to figure out the best speed and set up for cruising long distances. But MPG many times is really irrelevant because most boaters who ski and fish aren't looking for maximum efficiency, but maximum functionality for the use they want. I'm a little different because I genearlly use my boat for going distances, and therefore have tried to figure out my best MPG. Be glad you're not me becasuse my "best" is about 2 MPG cruising at about 2/3-3/4 throttle - but I have a 200 hp pushing a jet lower unit, which is about the most inefficient rig you can get.

But GPH is usually used.

Why? Becauase MPG is affected by boat hull, load, wind, current, etc. and therefore is difficult to make comparisons. GPH is strictly related to the HP being put out. GPH - for a given HP/size of engine - is or should be the same at max HP (~ max RPM) whether that RPM is pushing the boat fast or slow (which depends on the conditions). Wide open burns the same amount of fuel whether you're going 15 mph or 60.

The rule of thumb is that GPH for any given HP is 10% of that HP when the engine is running wide open throttle (WOT). So, any 85 hp engine running wide open should burn approx. 8-9 gallons per hour at WOT.

To measure this, you have to go out and run WOT for 20-30 minutes and then accurately measure the amount of gas you've burned.

You also want to know if your engine is turning the optimal RPMs at WOT, because that affects how much load is on the engine throughout the RPM band, which in turn affects the wear and tear on the engine.

Generally, the GPH will be 20-30% less at "cruise" speed, 3500-4500 rpms. That's probably where you'll get your best mileage too. Using a GPS and a fuel flow meter, I found my best RPMs for my engine was at about 4200 in terms of MPG, in general so that's what I use when I'm just trying to maximize fuel efficiency (as opposed to the times when I just want to get there fast). But again, mileage is affected by so many variables, all you can do is try to figure out if your GPH is fairly normal for your engine and then go from there.

 

[Fl_Richard]

Re: Took my boat out for the first time! MPG?

GPH For a 85 should be about one tenth the rated horspoer at side open throttle (WOT) so an 85 should burn about 8.5 gallons in an hour at WOT.

You said you get 33mph in your boat. At 8.5gph at WOT (33mph) you should GO 33 miles in an hour, burn 8.5 gallons and get 3.8mpg.

Not bad

At 20mph I'd guesstimate 20 mile in an hour, 6 gph and 3.3mpg

Thats what you got. 10 miles x 20mph and 6 gph=3 gallons. - PERFECT!

 

[henrye718]

Re: Took my boat out for the first time! MPG?

Shave your head it will increase aerodynamics. Unfortunatly boats are terrible on gas, Thats why I try to own aluminum boats open style.

This 16ft boat burns 3 gal per hour with 2 passengers and a 40hp engine the hull weights 300lbs. Max speed on GPS is 37mph.

 

[Todesengel]

Re: Took my boat out for the first time! MPG?

WOW! You guys rock! Just from those two posts alone I just about doubled my outboard knowledge lol. So from what it sounds like my motor is operating efficiently lol. The guy I got it from was a huge guy, and said him and his wife were to fat for the boat. They only ran half a tank of fuel through the motor the first year they owned it, and then it sat for a year. So I assume a tune up could maybe get me some increased GPH? I just wish I had a bigger fuel tank, fueling up at the Marina put a hurt on my pocket haha.

@Henrye - I'm bald, I'm already aerodynamic lol!

 

[Jack Shellac]

Re: Took my boat out for the first time! MPG?

Beautiful picture! Thanks for posting it. Having owned a Johnson V-4 for almost 20 years, I've always carefully read any boat test with this particular motor. There are a lot of variables, but GENERALLY, the boats of 17-18 foot size got the best gas milage at around 4000 RPM. This assumes,of course, that they are propped right, allowing 5500 RPM or slightly over at WOT.

 

[kenmyfam]

Re: Took my boat out for the first time! MPG?

Yes they use a lot of gas. MPG is not a real number due to wind and currents. 10% of your HP in gallons per hour at WOT is about what you will get. If you are pulling up a skier no issue then your set up must be close to perfect. More weight in the bow may help though. How is your hole shot ???

 

[Boss Hawg]

Re: Took my boat out for the first time! MPG?

My 70hp behind a 16' fiberglass bassboat burns exactly 1 tank per 30 pack Miller Lite - Go figure

 

[Todesengel]

Re: Took my boat out for the first time! MPG?

Hahahaha Boss Hawg! I will test my BPH(Beer per hour) when I take it back out for the weekend in two weeks.

@Ken - I would say pulling a skier it was close to 3 seconds until I got on plane from a stand still to WOT. I haven't gone from a stop to WOT without a skier yet.

 

[kenmyfam]

Re: Took my boat out for the first time! MPG?

Hahahaha Boss Hawg! I will test my BPH(Beer per hour) when I take it back out for the weekend in two weeks.

@Ken - I would say pulling a skier it was close to 3 seconds until I got on plane from a stand still to WOT. I haven't gone from a stop to WOT without a skier yet.

Sounds like your set up is pretty good then. My 140hp pulls them out like they are not there !!!