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Author Topic:   170 Montauk Fuel Economy
cape_rover posted 11-04-2003 09:25 PM ET (US)   Profile for cape_rover   Send Email to cape_rover  
I'm looking for a new Montauk (2003 or 2004) with a 90 hp 4-stroke engine and possibly the fishing package. Has anyone seen a good deal in the New England area? I live in Mass but would travel to NJ, NY, CT, RI, or NH.

Does anyone have the MPG figures for this boat? I haven't found it on this site yet. I've seen references from 4 - 6 MPG.

Maximus posted 11-05-2003 09:47 PM ET (US)     Profile for Maximus  Send Email to Maximus     
4+ MPG cruising the cape this summer on an 03 M170 w/4s.
jimh posted 11-06-2003 12:49 AM ET (US)     Profile for jimh  Send Email to jimh     
Fuel consumption is going to be directly proportional to the horsepower you use. You can figure about 0.5 pounds of fuel per hour per horsepower. Of course, how far you go with that horsepower depends on the boat. I'd guess that 50-HP will put you into the 25-MPH range with a 170 MONTUAK--just a guess.

How does that work out?

1 HR x 0.5 LBS/HR X 50 HP X 1 GAL/6 LBS = 4.2 gallons / hour

If you go 25-MPH with that much horsepower you'll have a fuel economy of about

25 miles/ 4.2 gallons = 6 MPG

Please use the MARKETPLACE forum for "Wanted to Buy" notices.

cape_rover posted 11-06-2003 06:14 AM ET (US)     Profile for cape_rover  Send Email to cape_rover     
I know gas is lighter than water but is it really 6lbs/gal? I was thinking it was closer to 8lbs/gal...
cape_rover posted 11-06-2003 06:46 AM ET (US)     Profile for cape_rover  Send Email to cape_rover     
Sorry, just looked it up, gas is 6lbs/gal.
lhg posted 11-06-2003 01:48 PM ET (US)     Profile for lhg    
To be precise, it's 6.2 pounds per gallon.
bobeson posted 11-06-2003 02:31 PM ET (US)     Profile for bobeson  Send Email to bobeson     

I own a 170 with the 90HP 4-stroke, and recently
installed a Standard Horizon digital fuel flow meter.
I've only used this boat once since installing the meter,
and that was nearly two months ago now (I've been way
too busy ashore!), but I was reading about 5.5-6 gallons
per hour at nominal cruising speeds of 21-24 knots
in a moderate Pacific chop of 2-3 feet. I have not
tested on glassy waters yet. Also, I have not performed
an accurate calibration yet, but the overall fuel
consumption out of the tanks seemed to closely match
the totals reported by the meter, so I suspect that
the 5% uncalibrated accuracy claim the manufacturer
gives is reasonable.

So, my estimate of fuel consumption is much closer
to 4MPG +/- 0.5 MPG at ~22 knot cruising speeds,
and definitely not 6MPG unless you are calculating
speed over ground with a favorable 2 knot current
and strong tailwind on glassy waters :)

Barney posted 11-06-2003 02:56 PM ET (US)     Profile for Barney  Send Email to Barney     
bobeson, Thanks for the information. One of the things I would like to know is does the economy improve for the 170 Montauk 90 HP 4-stroke at higher RPMs, say 4000 RPM versus 3500 RPM. I think it just might. A performance spreadsheet from a boat publication documents this. But I wonder about the data. Kinda of hard to do without a flow meter. Can you give us some more detail on the flow meter installation? Jim
jimh posted 11-06-2003 06:03 PM ET (US)     Profile for jimh  Send Email to jimh     
Typically for any boat/engine/propeller combination there will be a sweet spot that produces the best fuel economy with reasonable speed. It is hard to predict what that might be in advance. The individual boat/motor/propeller, the load on the boat, and the sea state would all affect it.

With most outboards the sweet spot will be below 4000 RPM.

If you have accurate fuel flow instruments, accurate speed instruments, and you have connected them together into a system, you can get real-time computation of fuel economy. This information can be used to adjust your throttle setting to maximize your performance as you operate your boat. In some cases it might be that a small adjustment in speed produces a large gain in fuel economy. Again, this depends on the situation.

As I demonstrated in the example above, the laws of physics tend to place an upper limit of about 6 MPH (for a 90-HP engine on a light weight planing boat like a MONTAUK). That is probably the best you will get. As others have reported, over a mix of conditions they see about 4-MPG.

At some point you just give up worrying about it and have fun. I probably burned 300 gallons of gasoline at close to $3/gallon on my 12-day cruise up the inside passage in the Pacific Northwest. It was a great trip and when it was time to get more gas I just put it on my credit card. I probably averaged about 2.5 MPG, which at the price of gas up there meant it cost me a dollar a mile. It was worth every cent of it.

Barney posted 11-06-2003 06:55 PM ET (US)     Profile for Barney  Send Email to Barney     
jimh, If I bought a fuel meter it would be an electronic toy. This is the first time I can remember anyone mentioning one of these devices installed on a new Montauk. I don't know a whole lot about them, and the thought of finding the sweat spot on the Montauk is of interest to me. However, I'm going to keep this boat simple.

Of course I don't mind going faster and getting better fuel mileage at the same time either. Mmmm. Jim

James posted 11-06-2003 07:35 PM ET (US)     Profile for James  Send Email to James     

I use my 170 Montauk with the 90 HP - four stroke, primarily for fishing and crusing in Raritan/Sandy Hook Bay, located in Central New Jersey.

My 170 hull is now painted (with Micron), as I keep the boat in a marina slip. My 170 Montauk planes at just about 3050 RPM. I would agree with Jimh, the 170 performs very well cruising at 3400 to 3800 RPMs. Crusing at this engine speed with a couple of people on board, and close to a full tank of gasoline, I typically get a very comfortable riding 24 MPH - 29 MPH registered on the GPS/WAAS. I have an hourmeter and a 27 gallon Pate tank, and I have tracked the GPH. Fuel usage is about 2.5 GPH. You can do the math.

Actually, the fuel usage of the 170 is sort of a non-issue for me. I get several fishing trips out a full Pate tank. Fuel dock bills to top off the Pate fuel tank are typically $10.00 - $17.00. More than once, the owners of nearby, bigger boats have half-kiddingly offered to trade fuel bills with me. I would estimate that deliberately trying to use up the 27 gallon Pate in one day, in my type of open bay use, would be a very tough exercise on the spine.

When the 190 Nantucket was first announced this past spring, I seriously decided to sell the 170 and move up. The dealer told me that I would probably lose half the boating season waiting for the new model to arrive. Also, my preferred engine power for that boat (the 150 HP - Four Stroke) was on the Mercury horizon but had not yet been released. I chose to wait and decide to trade up in the off-season. We had a very nice time with the 170 this year. My spouse and my "kids" (now 21 and 23 yrs. old) loved using "the little boat". The 170 does have offshore and rough-water fishing limitations, as any 17 foot boat can be expected to have. However, the 170 is easy to master and use. We had some very nice times with the 170 this year. I plan to keep it for at least another year.


Perry posted 11-06-2003 08:57 PM ET (US)     Profile for Perry  Send Email to Perry     
6+ MPG is not unreasonable on a 170 Montauk. If an Edgewater 185 c/c (18' 6" and 1600 lbs) can get 6.5 MPG and 2.9 GPH with a Honda 90 at 3500 rpm, a Mercury 90 should be able to get more than that on a lighter flatter Montauk 170. BTW, the Edgewater/Honda info is published and listed on the Honda Marine website under performance tests.
Barney posted 11-06-2003 10:25 PM ET (US)     Profile for Barney  Send Email to Barney     
I have referenced this before in another thread I hope you don't mind:
This shows miles per gallon is good a 4000 RPM and is best at 5000 RPM, weird huh! Jim
Jarhead posted 11-06-2003 11:00 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     
Yea but look at the gallons per hour... 4.7gph @ 4000RPM and 7.0gph @ 5000RPM...virtually the same mpg at both RPM...
Barney posted 11-06-2003 11:17 PM ET (US)     Profile for Barney  Send Email to Barney     
Jarhead, Yep that's correct and 23.1 MPH @ 4000 RPM versus 35.1 MPH @ 5000 RPM. Not much difference between the MPG at these speeds. Not that I would operate it a 5000 RPM for very long.

Look at the difference between the fuel consumption at 3500 RPM and 4000 RPM. Jim

Jarhead posted 11-07-2003 12:14 AM ET (US)     Profile for Jarhead  Send Email to Jarhead     
Those really are some weird numbers...

From 3500 to 4000RPM is a dramatic change between speed, mpg and range. ((0-0))

Nice reference page BTW...

Moe posted 11-07-2003 09:30 AM ET (US)     Profile for Moe  Send Email to Moe     
That's where it finally gets up on plane. Strange numbers indeed, from what I've seen reported.


cape_rover posted 11-07-2003 10:20 AM ET (US)     Profile for cape_rover  Send Email to cape_rover     
thanks for the reference - those are 2-stroke numbers, correct?
Barney posted 11-07-2003 10:28 AM ET (US)     Profile for Barney  Send Email to Barney     
Cape, Those are 4-Stroke numbers. At least that is what is said in the chart. Here are some more numbers from Forum members. These don't include fuel consumption:
cape_rover posted 11-07-2003 12:51 PM ET (US)     Profile for cape_rover  Send Email to cape_rover     
Your right it is a 4-stroke for the whaler. It looks like they tested with 2-stroks on some of the other boats. What's up with the pitch on the prop - It's a little blurry but does it say 23"???
Moe posted 11-07-2003 05:05 PM ET (US)     Profile for Moe  Send Email to Moe     
As I understand it, the 90HP 4 stroke on early 170s came with a 2.07:1 gearing (like the 115) and a 16" prop. Later ones use 2.33:1 gearing and an 18" prop. RPM per MPH should be the same on both.


Barney posted 11-07-2003 06:25 PM ET (US)     Profile for Barney  Send Email to Barney     
Yep, who knows where the 23 pitch came from. That wasn't the test prop for sure. MoeMan is correct on the current prop. Runs great. Jim

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