Fuel Economy with 115 Yamaha 4Stroke

[Saltwater Wade]

I just had a chance to take my new 190 out this past weekend. I ran the break in period and then did some cruising. I calculated that I got about 4.5 mpg with the bimini installed, but closed up. The wind was up a little also. This is my first larger size boat (previous 16' John boat with 40 hp 2-stroke). Should I consider this good fuel economy? What are you guys getting? I did notice the bottom of the boat is not completely smooth like fiberglass boats. Has anyone found that the Triumphs suffer due to this small amount of extra resistance in fuel economy?

Thanks,

Wade

[NCangler]

Hi Wade. 4.5 mpg is pretty good. That is about the best I can do with my Yamaha 150 4-stroke. The Triumph hull is not smooth like a glass boat but the boat is lighter, so I would think that the fuel economy would be as good or better. But I'm not sure if there have been any scientific evaluations of that.

[jack7265]

Wade, I also have a 2004 Yamaha F115 four stroke, and with my 190 Bay loaded for fishing and with another person, I calculated that I got around 4.3 MPG, which is close to your figures. I've looked at performace reports for other makes of engines that size and similar weight boats, and from what I can tell, these are good numbers.

Jack

[Putershark]

Well if you have to ask... My Honda 150 VETC is running 1.89 GPH average as of right now.

How?

1. Running a quick launch 3 bladed Stainless Prop. Such props cut a few knots off the top end speed I agree, but digs out of the water like a Space Shuttle launch
2. Always driven for quick to plane speeds (punching it to get on plane) but mostly ran and trimmed out at minimal plane speeds afterwards as I scout out new waters. Besides, the CD deck sounds much better at lower RPM's
3. High Grade / Octane Fuels (one burns less of the stuff IF the engine is not knocking and pinging
4. Mobil 1 motion lotion in the crank case, and filter mag installed on the oil filter.
5. Low water pick up and BMS plate mounted on the lower unit. Here again, to reduce drag and help get the hull on a plane as quick as possible.
6. Star Tron added to the fuel which helps keep it fresh and the octane from falling while being stored.
7. The hull is kept light so I do not draft as much water.
8. Maximum use of my Minn Kota trolling motor to include running on it instead of the big engine at times in no wake zones. Charging batteries though is much cheaper than pouring in fuel and a matter of fact, the last time time out... I came in on the trolling motor since my last fishing stop was less than 2 miles from the ramp.

This is all tracked in a excel sheet (as many here know) since I posted copies of them for everybody to use... This way you can find the sweet spots for which fuels and which prop combos returns the best yields for "your" boat.
If you don't track such items, trust me you are only guessing at those numbers

[Saltwater Wade]

Thanks for the feedback.

[NJWardy]

I have not worried about fuel economy. I knew when I got into boating that it was going to be a very expensive vice. Gas on the water is about $1.10 more per gallon than on land. But I guess I should monitor for performance...

[190bayguy]

puter-

You run 93 in your boat? Does the honda call for it?

Can you really notice a difference with higher octane/ (have you actually heard your engine ping?)

[Putershark]

• Last I looked at the pump I think it was only 91 octane? I only run either Chevron or Shell fuels due to their superior detergent packages and trust me, that is a lot of valves to get deposits on if one is not careful
• No Honda does not require it BUT these engine ECU's have "adaptive learning / programming" that is a carry over from their automotive units even though the engines (Automotive and Outboards) are NOT built the same as many think they are.
• Hard to hear any pinging on any outboard engine due to not having a muffler on the exhaust systems, but I did hear a engine rap one day when coming out of a partial throttle position going to full throttle position in the heat of summer one day. Here again in Florida, the cooling water temps going "into" your engine are in 80 degrees range for months, so you are not drawing off a lot of heat from the engine block. So if you truly understand what Octane is and does (this may help http://en.wikipedia.org/wiki/Octane_rating), and how environmental factors can can have both either a positive effect (such as in a rain storm) or negative effect (hot dry air) on "real time" octane numbers. It is then easy to see why the engine would rap some and the knock sensor would start backing up the timing to kill it.
• Most times though, the knock sensor that feeds data to the ECU will start backing off the timing in the engine long before one would actually "hear" it... Problem is, you are going to keep putting in more and more throttle to get the same return / speed. Well, we all know what giving the engine more throttle does to fuel burn rates
• My recommendation for everybody is the see what works the best for "your" area and the current weather conditions case in point... I run my Pathfinder (91 is recommended) on 89 grade fuel in the "cooler" months and suffer no ill effects in MPG. But to try to do such in the summer heat (unless is it going to rain almost constant while on that tank) and it will drop its MPG to the point that I am actually spending MORE money at the pump from burning more of the lower grade fuel and the boat is no different... Simple physics really, but one MUST test and track to find what works best for their application and the fuels in their area.
• The cleaner one keeps both the outside and inside of the engine though, the lower it's octane requirements will be.

[190bayguy]

puter-

I am a auto mechanic and very familar with octane, knocking so on and so forth (not bragging, just stating)

As an auto mechanic, I understand boats engines are different (but very much the same).

One thing I am having trouble understanding:

As you said the water temp running through the engine is roughly 80 degrees (which is high for water temp, at least compared to up north). Although in a car the water circulating is roughly 200 degrees (varying per application and other factors). Why would the 80 degree water vs 60 degree water have even that much of an impact?

nate-

[Putershark]

I love it Nate, another "Motor Head" so this should be much easier for you to picture than some of our other members. Hopefully though, I can help more picture how this all comes into play

Well, the biggest difference between the 2 cooling systems (after the thermostats open up of course) is the ability or more important, speed at which one transfers heat away from the engine. As you well know the hotter the engine (cylinder heads and intake manifold mostly) are running, the higher your octane requirements can / will become with all other things being constant...

So if you take my engine and put it in my local Gulf waters that are running 80 to 85+ degrees at X RPM's and then move it into waters that are now (for example) 50 degrees. The amount (rate) of heat transfer from the engine while running in the cooler water water temps is going to be greater for the same amount of water flow. Thus in the hotter water what needs to run on 91 octane to run at its full timing curve map, can now run on 87 octane fuel and not suffer any real measurable performance loss in the cooler waters.

This is unlike a "closed loop" cooling system like your typical automotive engine has which uses 15 psi (or more) of radiator cap pressure to raise the boiling point of the coolant. Much less, a thermostat which helps it transfer more (and at a more constant rate) engine heat for X amount of coolant flow. We also have to remember that these cylinder head temps soar much, much, faster in any boat engine. This is due to the amount of work / load that engine has... Let off the gas pedal in your truck and it will coast for quite a distance. Drop the throttle on your boat and it stops very quickly due to all the drag. Outboards have to work on a constant basis to keep the boat hull moving much more than your standard automotive engine. This is also way I state that rule #1 for saving fuel is... "Never drive a boat where you can drag it, for it burns much more fuel to get it to the same area "off" the trailer then on it"

Another good example of this uncontrolled (faster build up) of heat and how it effects octane requirements is when you get a car engine real hot and when you go to shut it off how they can rap and carry on and sound like you need to take out a stick to it to beat them it to death This is because the engine is so hot that is it slowly becoming like a Diesel engine in nature, and "trying" (or is) to run on compression alone long after the spark plugs are shut down... The Air / Fuel mixture is still exploding due to heat alone, not because it has any controlled ignition source.

So Outboards (much like Automotive or Aircraft air cooled engines) have a harder time in controlling heat transfer due to the fact that the inlet water temperature (as in the case of the outboard) changes more as the season's change. For many users, their biggest issue is in getting a 4 stroke engine "warm" enough due to the lower inlet water temps to get the engine oil hot enough to "boil off" all the moisture it collects. That crankcase moisture becomes very acid in nature as you well know and can create some internal engine havoc in its own right...

Here in Southern Florida though, we only combat with that issue (running too cool) for a few (very few) winter weeks. We on the other hand, battle with higher temps both Air and Water thus, our engines can naturally have a higher octane requirement for at least 6 months or more out of the year. Even summer months up North are not as bad of an operating environment as here even when the air temps push the 90 degree mark outside because the water the engine is drawing from for cooling, (transfer rate) is usually 15 to 20 degrees cooler. Here though it may be 87 degree water and 90 degrees outside. That is just not that much of a temperature spread to draw off much heat. And we wonder why back in the late 1980's why carb Mercury Outboards (painted black now) the fuel would boil in the lines and they would vapor lock and not start after running 20 miles offshore? Never shocked me as to how it was happening Yea, that is real smart... Lets paint the engine black and see just how "hot" we can make it run! Ha-Ha...

Heat, Friction, Engine Load, Weather (both in temp and humidity levels) all effect "real time" octane requirements. Though an engine can be designed to run on X octane level (87 for example) those design elements cannot really factor in for engine carbon deposits that either "lean out" the incoming air / fuel mixture due to dirty intake valves or plugged fuel injectors OR (which many forget) carbon deposits on the crown of the pistons that is in effect, making the compression ratio increase due to the now smaller, combustion chamber size.

So you take a new clean engine that has a compression ratio (for example) of 9 to 1 and "can" run on 87 octane fuel and not knock, but give it a few millimeters of carbon build up and is now almost 10 to 1 (or higher) compression on a few if not all cylinders now will knock even if you don't hear it doing such... And even if you do not hear it rap (knock) the knock sensor has and "is" backing off the timing curve and power output (much less RPM's) all at the same time...


Now Nate I am quite sure you have tapped on a running engine with a small hammer while at idle to test the knock sensor operation and see the timing curve jump to know what I mean...
Heat though is the issue plane and simple, and even worse in Florida when it comes to octane needs. The closer you can keep the engine to new (clean) both inside and outside the better you can transfer heat and as such, help manage fuel octane requirements.

So as I stated before, one needs to really test, track, and compare how "your" engine reacts to find the "sweet spot" for your hull and engine / prop combo in your area. Don't be shocked to find though, that as the engine gets some hours on it and it is getting warmer outside... That you find your ROI (Return on Investment) by running a higher grade and higher octane of fuel even if it is just jump to 89 octane shows a lower fuel burn rate and better performance on these newer 4 and some HO 2 stroke engines

One last item... 91 octane fuel on average is what now 30 cents more a gallon? So a 190 bay holds (if empty) 29 gallons total. So for a extra $8.70 not even the cost of lunch, to get fuel that may set in your tank for 6 months on end is the TOTAL cost difference between it and the lower octane grade of fuel. This while maybe returning better short term gains much less, long term gains by helping keep engine deposits in check to me is pretty dang cheap engine performance insurance in my eyes

Hope this helps?

Dave