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Author Topic:   Top Speed/Cruising Speed/Fuel EconomyRange
vdbgroup posted 07-13-2001 09:40 PM ET (US)   Profile for vdbgroup   Send Email to vdbgroup  
'81 Montauk '81 90hpV4 Johnson 13x17 prop: TOP Speed= 39mph Cruise=28-30mph Fuel Economy 4mpg/7.5GPH Avg. Load & Full Tank
'89 Outrage 18' w/ '89 Yamaha 150 13x17 prop:
TOP Speed = 45 mph Cruise 30-34mph Fuel Economy 3.3mpg/10GPH Avg. Load & Full Tank

Just Comparing Notes.

Hank posted 07-13-2001 10:36 PM ET (US)     Profile for Hank  Send Email to Hank     
Interesting data. For better comparison do you have the tach rpm readings at the noted speeds ?
Bigshot posted 07-14-2001 08:46 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
seems under pitched on both. GPH seems high too. Anyone else with these setups? My 90 Yamaha runs over 40 with a 17"SS. Cruise is 28-29 @3700 and 4+ gph.
vdbgroup posted 07-14-2001 11:52 PM ET (US)     Profile for vdbgroup  Send Email to vdbgroup     
RPM's Montauk Top=5,500 Cruise=4000-4300

RPM'S OUTRAGE 18 Top=4,900 Cruise=3800-4100

Note: 1981 Johnson V-4 set-up Optimum

1989 Yamaha V-6 Needs tweaking - in progress Top RPM Spec is 5,200rpm

vdbgroup posted 07-15-2001 12:01 AM ET (US)     Profile for vdbgroup  Send Email to vdbgroup     
Bigshot, your consumption of 4GPH seems high given a cruise speed of 28 mph translates into 7 mpg. I have heard the Yamaha 3cyl 90 2strk(which is what I assume you have) is very efficient, but 7 mpg, is OUTSTANDING, really? If so, I am going to Yamaha 90 3cyl asap.

Also, I believe your HP rating is at the prop where the '81's were rated at the head, so I would expect a little better on top end speed. I have never gotten over 42, usual top end is 39 mph.

Bigshot posted 07-15-2001 11:14 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Your motor being a 81 is the big dif. They are rated at the head, it is 20 years old and a crossflow type motor. Crossflows are dependable etc but thirsty. Old school technology. All newer engines are loop charged which burns a lot less fuel. I ran a 6 gal tank for about 1 hour and 20 mins at cruise so say 4-5 gals per hour. It gets about the same as my Johnson 70 did. Great engine and purrs like a kitten at 35-3700 Rpm's. I highly recommend it. My buddy back in 84 replaced his 81 70 Johnson on his Newport with a 90 johnson and was amazed at the higher gas consumption. Just FYI!
whalernut posted 07-15-2001 08:29 PM ET (US)     Profile for whalernut  Send Email to whalernut     
Bigshot, you are right on track with the Cross Flow V-4 engines being dependible, but thirsty! That fits my 1975 85h.p. Johnson to a "T". It is fast, runs great still,even trolls great now since I changed to Denso brand plugs, but sucks a ton of fuel, even on my light weight 73` `16 Currituck. Regards-Jack Graner.
simonmeridew posted 07-15-2001 08:51 PM ET (US)     Profile for simonmeridew  Send Email to simonmeridew     
Just tried out my new ss Rapture 13 X 17 prop today on Lake Champlain.
'84 Montauk, '99 Johnson 70, : Cruise @ 3700rpm, 21.8 mph by GPS (not knots).
So this is a "loop-charged" engine?. Absolutely runs flawlessly. The new prop is nice, seems to go from stop to 20 mph or so very smoothly, planes quickly, but not a real good test, with 4 people in the boat: 2 in the bow and 2 behind the console, with all the lunch and gear bags the women bring to maintain creature comforts. Can't tell how much gas we used; went 25 miles, maybe used 6 gal or so???
simonmeridew posted 07-15-2001 09:11 PM ET (US)     Profile for simonmeridew  Send Email to simonmeridew     
When I got to the launch ramp, a guy was just backing his Rinker I/O down into the water. He was all alone so I offered to help by holding the bow line which he was going to tie onto the trailer. So I took the rope, and walked down the dock as he backed in. Just as the boat slid off into the water, I noticed that the rope was just coiled onto the bow not attached at all. The boat slipped out into the lake a ways, I yelled to him to haul a** and get out of the way and I'd back my whaler down and retrieve his boat. This would be the time my launch went perfectly, thank heavens, I put him on his boat which he started and promply backed hard aground into the mud by the dock. I loaded my boat then took a line off his bow to pull him off. Talk about a way to start a boating day. We were well underway when I suddenly thought, I wonder if he cleaned the mud from around the water intakes on his I/O? When things go bad...
Hank posted 07-15-2001 11:02 PM ET (US)     Profile for Hank  Send Email to Hank     
When it comes to fuel consumption I think it is more nearly correct to compare GPH at the same RPM and Engine rated HP. A ROUGH rule of thumb for fuel consumption (at least on older 2 cycles) is .1 GPH per shaft HP at rated RPM. For example, a 90 HP would have a fuel consumption at 5500 RPM of 9 GPH.

Roughly, as RPM varies, fuel consumed is proportional to RPM. That is, at 3700 RPM, fuel consumption would be expected to be about 3700/5500 times 9 GPH or 6 GPH.
MPG varies widely with boat conditions. Note for example, that a boat might go 21 MPH at 3700 RPM or 29 MPH at 3700 RPM depending on load, prop pitch, etc. Since fuel consumption in GPH, however, is mostly dependent on RPM. for the 21 MPH boat MPG may be 3.5 MPG while the 29 MPH boat is getting 4.8 MPG .

vdbgroup is getting his data at 4000 to 4200 RPM. Bigshot is getting his data at 3500 to 3700 RPM. Both have 90 HP engines . I should think that vdbgroup should show 14% more GPH.
(4000/3500 = 1.143 )


Bigshot posted 07-16-2001 01:06 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Best way to do it is take a 6 gal and fill it half way and set it at cruise and see how long it lasts. If it 1/2 hour, then 6GPH, etc.
OutrageMan posted 07-16-2001 01:41 PM ET (US)     Profile for OutrageMan  Send Email to OutrageMan     
I have a Standard Horizon fuel flow gauge. With my Yamaha 250 V-x I get the following results...

3400 RPM, 22 mph, 11.2 gph
3900 RPM, 29 mph, 14.5 gph
4200 RPM, 33 mph, 17.4 gph
5200 RPM, 43 mph, 29.9 gph

This is on a 91 22' Outrage w/Whaler Drive. I am turning a 17 pitch Mirage Plus prop with the small vent hole plugs installed.

Bigshot posted 07-16-2001 02:07 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
OK! For us who do not have flowscans, the best way is....Man those 250's are thirsty compared to a 225. My 225 runs about 12gph at 3900+/- and about 23 WOT. By the way Kids, motors will burn roughly the same amount of gas per hour(GPH) no matter what boat they are on. ie: a 250 Yamaha will burn 14gph at 3900rpm on about any boat. But it might get 3.5 MPG or .5MPG depending on the speed. When you read Boating mag and they show a 20 Wellcraft with a 200 Johnson and a 19" pitch SS prop and are getting 5800 rpms at 47 mph. If you have a 20 BW with a 200 JOhnson and a 19" SS prop and redline at 5800 on your tach, you can pretty much use the Wellcrafts numbers for a very close estimate of GPH, MPG and speed. The engine will burn the same amount of gas at a certain rpm no matter what it is pushing. It does not know how fast it is going. All it knows is it is running 3800 rpms and is propped to hit max rpms. So in a nutshell a 25 outrage with a 15" prop and a 225 will burn the same amount of gas at 4000 rpms as a 21 checkmate spinning a 23" going twice as fast. Main difference is the checkmate is getting 4mpg and the whaler 2.
Contender25 posted 07-16-2001 03:05 PM ET (US)     Profile for Contender25  Send Email to Contender25     
To make you all feel better:

2 200 1999 Yamaha Saltwater series Carb'd turning ?pitch saltwater series SS props.

Cruising speed 38-42 MPH @ 3400 RPMs 1.8-2.0MPG 18-22 GPH

Top Speed 60-65MPH @ 5200RPMs 1.1-1.4MPG 38-42GPH.

Curious to compare with LHG's 25 with the old motors?

Bigshot posted 07-16-2001 03:15 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Contender, that's not bad. You are only burning 19-21 GPH per engine(wot) compared to his 29.9.
tbyrne posted 07-16-2001 05:25 PM ET (US)     Profile for tbyrne    
As I look at the gph numbers, I am struck by how accurate that "10% rule" is. Outboards almost invariably use fuel at a gph rate of 10% of their rated HP at max throttle. That is, a 200 hp motor uses 20 gph, a 60 uses 6gph, etc. In looking at boat tests, this even seems to be true for both 2-strokes and 4-strokes.

("Of course, your mileage may vary. . .")

Bigshot posted 07-16-2001 05:43 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Works for WOT pretty well. Any formulas for cruise speeds?
Hank posted 07-16-2001 06:38 PM ET (US)     Profile for Hank  Send Email to Hank     
See my post above.Fuel usage in GPH is roughly linear with RPM. That is, Cruise RPM divided by WOT RPM times GPH at WOT equals Cruise GPH. Estimate WOT GPH at .1 times Rated HP ( or 10% rule , same thing).
Estimate GPH at any RPM the same way.


SuburbanBoy posted 07-16-2001 06:42 PM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
The difference between the 2-strokes and 4-strokes at WOT (wide open throttle) should be small. I would believe that both are tuned for efficiency in that range. Where the 2-strokes get killed is generally anywhere between idle and WOT. The amount of un-combusted (i.e. raw fuel) fuel spewed at part throttle is quite large. 4-strokes handle part-throttle much better. Yes, I know that there are injected 2-strokes, and for the most part they are a big improvement, but there is still carry over to the exhaust. So if you use your boat for water skiing, tubing, etc. the 2-stroke vs. 4-stroke issue can't be settled on fuel economy issues alone. Also, Hank's rule of thumb seems to hold up quite well for both types of engines for the same reasons.


lhg posted 07-16-2001 06:59 PM ET (US)     Profile for lhg    
In reply to Contender's request, my old 1997 Merc 200 EFI's, running 23" pitch Merc Laser II's, get combined 2.0 mpg at 35 MPH cruising speed. Top speed about 63, but I don't know mpg, since it's rarely run that way.

My REALLY old cross flow Merc 115's, in line 6's, get about 3.0 mpg on the 18 Outrage.

Contender25 posted 07-16-2001 09:59 PM ET (US)     Profile for Contender25  Send Email to Contender25     

I thought you used to have a set of early 90's Mercs on your outrage. I was curious what the #'s on those were.

Bigshot posted 07-17-2001 10:06 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Hank, doies not work in that scenario. i do not burn anywhere near 6 gph at 3700, more like 4-4.5.
lhg posted 07-17-2001 03:04 PM ET (US)     Profile for lhg    
Contender - yes, originally, the 25 outrage had 1989 Merc carburated 200's, 2.4 litres. If they hadn't gotten stolen, I'd still have them.

They were only slightly less efficient, maybe about 1.75MPG at cruising speed. The EFI engines are lot quieter, but not any faster, from what I can tell. The EFI's are much
more trouble free engines. If I had to buy another set of new engines, I'd still buy the EFI's rather than become an "on the water" consumer tester for Optimax's!

Bigshot posted 07-17-2001 03:29 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I like that phrase lhg. It seems that every boat I buy I am an "on the water long term tester" The newest engine I have is a 94.
Clark Roberts posted 07-17-2001 05:06 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
On a recent run from Daytona Beach, Fla. to Captiva Island, Fla (down east coast and accross Okechobee Waterway to Fla's west coast) 320 miles each way , four boats got the following avg mpg for the trip: My 21 Revenge with 2000 Merc 135 Opti-max>5mpg ; David Day's 22 Revenge WT/WD with 2001 Merc 225 Optimax> 3mpg; Bill Clark's 23 Conquest with twin 1999 Merc 135 Optimaxs> 2.5 mpg and Richard Rosier's 24'7" GW CC with 2001 Yamaha 250 > 1.5 mpg... We cruised at mostly 30mph and had lots of idling in slow zones and locking through. Clark... Spruce Creek Navy

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