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Author Topic:   OUTRAGE 18 with 115-HP
dandowneast posted 12-04-2014 05:20 PM ET (US)   Profile for dandowneast   Send Email to dandowneast  
[This author says that he is] starting to look for an Outrage [18], [and he has] located one powered with a Yamaha F115 four-stroke-power-cycle outboard engine. Most [of the Boston Whaler OUTRAGE 18 boats that] I have seen over the years are running with 150-HP. Is this hull under powered with the 115-HP?
Peter posted 12-04-2014 07:35 PM ET (US)     Profile for Peter  Send Email to Peter     
Based on having had an Outrage 18 with a V4 140-HP two-cycle and a V6 150-HP two-cycle, in my opinion, the Outrage 18 with a 115 four-cycle would be under-powered for me. I think that is why you see so many with 150's rather than 115's.
bkovak posted 12-04-2014 08:21 PM ET (US)     Profile for bkovak  Send Email to bkovak     
I have had both an 18 Outrage with a 115 and one with an older 150. I saw very little difference in performance and actually thought the 115 was a good choice due to the lighter weight and better fuel economy. There is a motor performance chart in the reference section here that shows the comparison of these two size motors on a newer 19 Nantucket (Outrage). If setup properly and propped right, you will not have any significant drop in performance with the 115! It's a good fit for the classic 18 Outrage and will be more economical to operate.


Marko888 posted 12-04-2014 08:31 PM ET (US)     Profile for Marko888    
The key words in Peter's post are "for me". I think the answer to the question is very dependent upon where and how you plan to use the boat, and somewhat dependent upon what boat and power combinations you have owned in the past. If you are used to boats having the maximum rated power, then the 115 may underwhelm.

Many have the Yamaha F115 on Outrage 18's and are totally happy with the 38 tp 40-MPH top speed and frugal fuel use, despite some suggesting the combination is underpowered.

Alternatively, those who have 150's on this hull are also happy with their 45 to 48-MPH boats and extra boost to push heavy loads, or to pop skiers up out of the water.

I re-powered from an old 150 V6 to a new 2-litre 140-HP four-cycle on my Outrage 18 and am totally happy. My boat has less torque and won't do 45-MPH any more, but it doesn't matter TO ME. The boat uses half the fuel, still has enough get up and go to pull my nephews around on a tube, and is a LOT more enjoyable due to less a noise and fumes.

Do some searching and you will find much discussion about power choices for this hull.

Peter posted 12-04-2014 10:26 PM ET (US)     Profile for Peter  Send Email to Peter     
There is more to the HP story than top speed. I rarely ever ran my Outrage 18s at WOT. But I did run them with a fair number of passengers from time to time and it was during those times that the extra displacement and higher load carrying capacity of the 150 came in very handy. Also, the larger displacement allowed the motor to run about 500-RPM slower at cruise speed producing less noise and a more relaxing ride.

No one I know has ever wished they had less HP on the transom but many have wished they had more. It's nice to know its there if you need it.

Any modern outboard sold today will be more fuel efficient than any motor that originally came with an Outrage 18 when sold new. The fuel efficiency difference between a modern 115 and 150 will be minimal and in my opinion that shouldn't even be a factor in the HP decision these days.

Peter posted 12-04-2014 10:28 PM ET (US)     Profile for Peter  Send Email to Peter     
One other comment. If I had to be stuck with a 115 4-stroke on the transom of an Outrage 18, I would get one with the largest displacement possible. A 4-stroke needs about 20 to 25 percent more displacement to match the power curve of the same HP 2-stroke.
bdb posted 12-05-2014 09:32 AM ET (US)     Profile for bdb  Send Email to bdb     
115-HP Mercury FOURSTROKE [and to disambiguate, NOT the one made by Yamaha] with full tank and 375-lbs of bodies: cruise at 25-nautical miles per hour, 4900-RPM, 4.6-GPH. Top speed 36-nautical miles per hour. RARELY can go that fast comfortably and safely.
Marko888 posted 12-05-2014 10:31 AM ET (US)     Profile for Marko888    
As noted above, it depends upon how you wish to use the boat, and what your expectations are.

The cruise RPM argument is only valid in comparing two engines of like technology and generation. Yes, an F150 will use less revs than an F115 and be more relaxed. However, an F115 will be a whole lot more pleasant at 4500-RPM than a 1990's V6 2-stroke at 3800-RPM.

My wife's 2.0L Audi is a lot smoother and more relaxed than my 4.0L Tacoma at the same rate of travel. Displacement alone is a small part of the overall equation.

Try to get a ride in a few different setups and then you'll know exactly what will make you happy

acseatsri posted 12-05-2014 10:55 AM ET (US)     Profile for acseatsri  Send Email to acseatsri     
After having owned an 18 Outrage that started with an old 150 Evinrude crossflow and repowered with a Mercaha 115 four-cycle, I would definitely not hesitate on the 115 unless you're pulling skiers a lot or run with unusually heavy loads. My top speed with the 115 with T-top, fully loaded including full fuel, and three people aboard was 34 to 35-MPH.
Elaep, long a member here (may he rest in piece), had the same set-up minus T-top and with a Yamaha 115. His top speed was 39-MPH and swore by the 115.
jimh posted 12-05-2014 11:27 AM ET (US)     Profile for jimh  Send Email to jimh     
I do not think there is any basis to anticipate that you will have a difference in fuel economy between an OUTRAGE 18 with a 115-HP engine and one with a 150-HP engine based on the notion of the engine's maximum horsepower. Assuming the engines are of similar technology, when they push the boat at a certain speed they will both need to produce the same horsepower. And when making that horsepower they will burn about the same amount of fuel. There may be some small variation in rate of fuel used per horsepower--this is called the brake specific fuel consumption--but it is probably not going to be very significant, with the possible exception if your ran the boat at some certain speed which highly favored one engine's BSFC curve over the other. For example, if you planned to run at a boat speed where one engine was at maximum throttle and the other engine was throttled back somewhat for that same boat speed, it might occur that the BSFC would be different, and one engine might be more fuel efficient than the other.

There is a train of thought--perhaps I ought to call it wishful thinking--that if you have an engine with a lot of power and you run it throttled down all the time it will get better fuel economy--run at a lower BSFC operating point--than an engine of lower rated horsepower that was running at a wider throttle setting. Whether this occurs in reality depends on the engine designs and their BSFC curves. If you could get some real data about the BSFC of the engine, you could work out the fuel economy at certain speeds and loads and make a comparison. But in the case of outboard engines, you never see their BSFC curves being published. You can't say for certain what is going to happen to the BSFC with throttle setting, engine speed, and load. You can only hope that a larger engine running throttled down might get better fuel economy, or, conversely, that a smaller engine running with wider throttle will get better fuel economy. I just don't see any way to predict this reliably.

Now, having said that, you can count on the engine running throttled down to be running at lower RPM, and thus it should be making less noise and maybe less vibration. And it is probably experiencing less wear and tear, on the basis that is running at a lower percentage of its maximum rating.

jimh posted 12-05-2014 01:38 PM ET (US)     Profile for jimh  Send Email to jimh     
jcdawg83 posted 12-05-2014 01:41 PM ET (US)     Profile for jcdawg83    
Jim, I am not a physicist or an engineer, but what you seem to be saying is that it takes a certain amount of energy to move a given boat a certain speed regardless of horsepower, so the energy required is the same and therefore, fuel use should be the same. If this is true, wouldn't a 90 hp three cylinder outboard and a 200 hp V-6 outboard use the exact same amount of fuel to push the same boat 20 mph?

I'm not certain, but I don't think this would be the case.

jimh posted 12-05-2014 01:58 PM ET (US)     Profile for jimh  Send Email to jimh     
The boat moves at a certain speed when driven by a certain horsepower. The boat does not know if that horsepower comes from a big engine throttled down or a smaller engine running near full throttle.

The fuel efficiency of any practical internal combustion engine is not a perfect constant over its entire range of engine speed and power output. The efficiency at which the engine converts fuel to power is its Brake Specific Fuel Consumption or BSFC. For many larger engines you can find a curve that plots the BSFC as a function of engine speed and engine load. There are two dependent variables: the engine speed and the load on the engine. An engine running at high speed with no load has a certain BSFC and at that same speed under full rated load it has a difference BSFC.

If you had all the data about two engines, you could figure out which engine was going to most efficient at a particular engine speed and load, and you could then set up the boat to take advantage of it. The shape of the BSFC curve can be quite variable for each engine. The notion that running throttled down will always give the best BSFC is not always true.

Making prediction even more complicated is the influence of the outboard engine gear ratio. A larger engine probably will have a lower (numerical) gear ratio. You might use a propeller of different pitch with engines of different power. Now you have another influence on the comparison--the propeller efficiency.

Taking a look at automobile engines and their constant quest for best fuel efficiency, you don't see them going to really big engines and loafing along at low throttle to maximize fuel economy, but, on the other hand, on a boat that is running on plane, the engine is running at much higher throttle than highway-cruise in a car. It will take a lot of careful analysis to figure out what engine is going to return better fuel economy on a boat being run at a particular speed. As far as I can tell, what I said is quite reasonable. I said:

I do not think there is any basis to anticipate that you will have a difference in fuel economy between an OUTRAGE 18 with a 115-HP engine and one with a 150-HP engine based on the notion of the engine's maximum horsepower.

If you run the boat at moderate planing speed with either engine, they will probably burn about the same fuel. Of course, if you run the 150-HP at full throttle and push the boat to a faster speed than it could ever reach with the 115-HP, you are going to burn more fuel and probably see the MPG drop. To tell which engine will get the best MPG at say 27-MPH cruise, I think you have to just test them under those conditions. I can't see any way to predict which will be best. I would not try to go to the bank on the basis that one is going to be much different than the other.

jimh posted 12-05-2014 02:03 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is a chart of the BSFC of some actual engine. There are curves for three load conditions. As you can see, for each load there is an optimum engine speed for best (lowest) BSFC.

jimh posted 12-05-2014 02:08 PM ET (US)     Profile for jimh  Send Email to jimh     
If you look at the above BSFC curve, you see that for the 50-percent and 100-percent loads, the best BSFC is around the same engine speed, 3,300-RPM.

Let us suppose that we had another engine that was half as powerful as this engine, but had the same identical BSFC curve. When we compare the two engines we would see that the smaller engine running at 100-percent load actually is slightly more efficient at making power from its fuel than the larger engine running at 50-percent load. This is counter to the notion suggested that the bigger engine under lighter load will always be better.

jimh posted 12-05-2014 02:10 PM ET (US)     Profile for jimh  Send Email to jimh     
The chart above comes from

which has more discussion about BSFC and engine speeds and loads. See the section on the influence of throttle on BSFC. When the engine is "throttled" it has to work harder to pull in air.

jimh posted 12-05-2014 02:26 PM ET (US)     Profile for jimh  Send Email to jimh     
I did not intend to drag the OUTRAGE 18 question into BSFC territory. I just wanted to offer the advice that one should not expect to find any big difference in fuel economy between a 150-HP and 115-HP engine in typical use.

An OUTRAGE 18 with 150-HP has performance that reminds me of driving a very sporty car--a sports car, really. It goes fast and goes fast very quickly.

Marko888 posted 12-05-2014 05:36 PM ET (US)     Profile for Marko888    
I think the analysis JimH has presented is fair, as long as both the 115 and 150 engines utilize the same design and fueling technology, such as Etec 115 vs Etec 150, or F115 vs F150.
dandowneast posted 12-06-2014 02:29 PM ET (US)     Profile for dandowneast  Send Email to dandowneast     
Thank you all. I appreciate the wealth of experience and information here on CW.
Peter posted 12-06-2014 09:48 PM ET (US)     Profile for Peter  Send Email to Peter     
Below is a link to a graph of comparing the fuel consumption of an E-TEC 115 versus an E-TEC 150 in relation to boat speed on the same model boat.

As you will see in the graph, the fuel consumption of both motors is quite similar at most boat speeds with the 150 consuming less in some cases. While the hull is not an Outrage 18, the same motors on an Outrage 18 will produce similar results.

In short, to the extent that there is any fuel savings to be had by choosing the smaller motor, they will be minimal at best. But choosing the smaller motor will limit the capability of the Outrage 18. I think the extra cost of the 150 is worth it so as not to limit the capability of the Outrage 18.

Keeper posted 12-13-2014 11:30 AM ET (US)     Profile for Keeper  Send Email to Keeper     
We have an 1986 18 Outrage with an Evinrude E-TEC 115 and very happy with the economy and performance, , we are on the West Coast where conditions rarely allow us to run at or near WOT.

I have two friends with 18 Outrage hulls equipped with newer Yamaha F150 four-cycle outboards, and I will say this: our boat handles the rougher weather significantly better in rough waters largely due to the reduced weight--much less bow slap.

If my boating was done in primarily calm waters where I'd be able to run in the higher RPM range for longer periods, then I'd greatly consider a 150. Also, if I were having four people in my boat frequently, I'd consider the 150 for that extra grunt to get up on plane. But a 115 is a good choice if the reasons I mentioned above fit your needs.

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