Fuel milage question

[crb478]

I currently have a 1990 Sea Pro 180 CC that reportedly weighs 1550lbs. I bought the boat without an engine because it was cheap, in solid shape and I had been given a 1996 Evinrude 60 hp. I wanted the boat to fish primarilary in fresh water lakes where I do not have to travel far before I start trolling or bottom fishing. I realised that the boat was under powered( the max HP is 140), but wanted to try it out since it would put me on the water without spending any more money. The 60 HP motor pushes the boat up to 28 mph in calm waters, but even throttling back to about 22 mph it still burns almost 6 gallons per hour.
Since getting the boat together I picked up a 1975 Johnson 115 and with help from reading several post here got it running. It appears to be a really low hr motor that was left at a towing company for over a decade until they decided that they wanted the boat removed because it was in their way. I plan to put this motor on the boat, but have seen where this series of motors have been referred to as gas hogs. So I have three basic queations.
1) Besides a good link and sink with clean carbs is there anyway to improve
the efficiency of these motors?
2) If I throttle the 115 back and cruise at 25 to 30 mph do you think that
the fuel consumption will be simular to that of the 60 hp motor at the
same speed since the 115 will not working as hard?
3) What would you estimate the top speed will be with the 115 on the boat
instead of the 60hp?

Thanks for any opinions or advice, I would love to repower with a newer 90hp motor, but that will be a few years down the road.

 

[Silvertip]

Re: Fuel milage question

The 115 will burn about 11.5 - 12 gallons of fuel per hour and possibly more at wide open throttle. I doubt you will see 6 gallons/hour at 30 mph but 7 or 8 may be a resonable target. There are a couple of ways to look at fuel economy. If the max you can get is 22MPH with the 60, the 115 should do 40 or better. So if you only have to run half as long to get where you are going, the 115 becomes nearly as economical (from a dollars and cents standpoint) as the 60 if you run wide open.

 

[HighTrim]

Re: Fuel milage question

I had been given a 1996 Evinrude 60 hp. QUOTE]

Sigh Why can I never find these free motors !

 

[seabasser]

Re: Fuel milage question

if the motor was free i wouldn't worry about the gas....you can buy a lot of gas for the 10k or so that a new one would cost.......that beigh said they are gas hogs. my dad had that same style 90 and it burnt the same gas as a my 150 merc.

 

[jtexas]

Re: Fuel milage question

couple things come to mind for optimizing fuel economy:
set the engine height & trim to where you get & stay on plane at the lowest possible throttle setting.

prop for efficiency (check the prop forum). also make sure the prop is undamaged.

jettison as much weight as possible.

push the throttle up to WOT then throttle back to your cruising speed - as the butterflies close, the timer base will stay fully advanced for about the last 1/4 throttle or so - same RPMs for less fuel.

 

[jay_merrill]

Re: Fuel milage question

I have a 1972 Johnson 65hp on a 17.5' Glassmaster trihull, with a 15" pitch wheel on it. My speedo is a NOS Airguide that reads up to 35mph - it shows from 25 to 27mph at WOT/5000rpm and about 22mph at 4200 rpm, which I usually run it at. Both scenarios include two people in the boat and light gear. My fuel consumption is almost identical to yours at the 22mph speed, so I think your numbers are right at what you should expect.

When I first put the motor on the boat, it had a 17" wheel on it, which would push the boat 28 to 29mph with the same load in the boat. The problem was that the WOT rpm was only 4600 and that is too close to the bottom of the acceptable rpm range (4500 - 5500) at WOT for this motor. Any additional people or gear in the boat would have me running under 4500/WOT and that's not good for the motor!

The question of going to a larger engine has many answers and it just depends on what you want. As some have pointed out, you will burn a lot more fuel per hour with the 115 but you will go a bit faster, so the economy stated in mpg may not be that different. I do think you will burn more fuel than you are now though, simply because the amount of power required to push any vehicle faster is not linear - you won't end up with a "twice as much power = twice the fuel consumption at twice the speed = same fuel consumption." That said, you have a free motor in pretty good shape and there is one very good reason for putting it on the boat, namely that it won't hurt you too badly on fuel while giving you a great deal more flexibility in terms of load in the boat. Frankly, the only reason I haven't put a 115 on my boat is that I sometimes run 30 - 40 miles out in the bayou and the "skinny" 65hp allows me to hang a kicker ('69 6hp Johnson) right on the transom, without interfering with the main powerplant.

 

[crb478]

Re: Fuel milage question

J Texas, I am familiar with setting up the engine height, but I was unaware that throttling back from WOT would keep the timer advanced I will definately try that.
Is there anyway to tune the carbs or put different carbs on it and pick up a little more effieiency? I am fairly decent at getting Harley carbs tweeked to give the best performance and milage (my Road King gets 50mpg), but then again we are talking 4 strokes not 2 strokes. Can these be rejetted? Can I keep reading the plugs and changing jets until I get the best color on the plugs?
I only got the 60 HP for free as the boat was repowered and it needed a little work. I paid a whopping $100.00 for the 115, the controls two 6 gallon fuel tanks(both of which leaked), and a steering helm. That guy had sold the trailer and was trying to get anything he could out of the motor. The boat was trash.
I plan on switching motors after the first of the year, but I want to do all the maintaince and some of the tweeking while it is still on the stand because it is much easier to work on there.
Thanks again for all the suggestions and insight! I am open to any more ideas you all might have.

 

[crb478]

Re: Fuel milage question

Frankly, the only reason I haven't put a 115 on my boat is that I sometimes run 30 - 40 miles out in the bayou and the "skinny" 65hp allows me to hang a kicker ('69 6hp Johnson) right on the transom, without interfering with the main powerplant.
Jay Merrill


I plan to put a kicker on this one also as soon as I get the motor situatuion worked out. I have a 1960 Evinrude 18hp and a kicker bracket waiting to be mounted. I plan to run it most of the time I am out there and only use the main engine between fishing spots.

 

[Mr.Stuart]

Re: Fuel milage question

I have a 78 115 on an 18 foot starcraft, it's an aluminum boat so it's going to be lighter then yours (1,800 lbs loaded I think) I can run about 5 hours on an 18 gallon tank, the boat will cruise at about 45 MPH, it's a gas hog, I've seen as others have suggested that if you throttle up to get on plane, then back off the throttle to hold your cruise speed, it seems to do better on fuel, but when I first got mine, I figured, 18 gallon tank, 4 cylinder engine, I figured I'd be able to cruise all day on maybe 5 or 6 gallons of gas, but what did I know, I was a new boater, I even ran the thing out of gas one day on the river because I didn't believe the fuel gauge, they just like to suck gas, and when the fuel gauge in mine reads empty ....it's empty

 

[kenmyfam]

Re: Fuel milage question

As has been said above and in several other threads. 10% of the hp in gallons per hour is about what you will get from any motor at WOT. Significantly less per hour when backed off a little but distance per gallon is similar no matter what.
The only way to do better than that is to paddle it or install a sail.

 

[Mr.Stuart]

Re: Fuel milage question

As has been said above and in several other threads. 10% of the hp in gallons per hour is about what you will get from any motor.
The only way to do better than that is to paddle it or install a sail.

Hand the oars to the kids, that's what I do, then I usually have to duck when they swing them at me..........

 

[flabum]

Re: Fuel milage question

If I'm not mistaken, your 60HP is a loop charged engine. The 115 you want to put on is a crossflow engine. Crossflows generally burn more than loopers do, so comparing the two is unfair. You probably would get better economy (not much) with a looper 120, but those crossflow V-4's are hard to beat for reliability and ease of service. 6-7 gallon per hour on a rig that weieghs 2000#'s (1550# boat and 400# motor) is acceptable. I think you will have the same economy at the same speed or a little faster. As for top speed, with the right prop and setup and still getting good holeshot you should get between 45 - 50 out of it. I have a 16' ski boat that weighs 600#'s with the same motor and getmid to high 50's with it.

 

[crb478]

Re: Fuel milage question

Thanks for all the replies, I am going to try swtching motors after the first of the year. I really want to get the 115 running as efficiently as possible, basically I just like things to be right. I think it is worth switching them just to have the extra top end just in case I ever need it. Thanks Again