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Author Topic:   New Yamaha F115B
FISHNFF posted 09-03-2015 03:38 AM ET (US)   Profile for FISHNFF   Send Email to FISHNFF  
If you recall, my 1988 18 Outrage was stolen from in front of my house here in San Francisco and was later recovered in San Jose, stripped of motor, accessories, and electronics. After researching motors, I decided to to replace the stolen 13-year-old Yamaha F115 with a new Yamaha F115B, a lighter weight, more powerful, more technologically-advanced engine.

After putting 50 hours on [the new Yamaha F115B engine] I can say I see almost no advantage other than acceleration is noticeably quicker. The Command gauges with fuel flow are nice, and the F115B does look nicer. The top boat speed is the same. Fuel economy is about the same, but I am not exactly sure; I need a bit more time. The engines have equal quietness.

The propeller I am using is different from what I had in the old motor. I now have on a Yamaha 17-inch K propeller. The F115B can only turn 5700-RPM with it. I tried this propeller on the old motor and remember turning 5900-RPM.

Also, the F115B is mounted one-hole-up, same as the old motor. I do see water spraying up from either side of the lower unit. Why this would occur now, I don't know, but the motor [will be raised] up one hole when it goes back for service.

I was expecting an increase in performance from a motor with bigger displacement, lighter weight, and 13-years of technological advances. Not so.--FISHNFF

Peter posted 09-03-2015 06:33 AM ET (US)     Profile for Peter  Send Email to Peter     
From what I've read, the F115B model has a WOT operating range of 5300 to 6300. Your old F115 had a WOT operating range of 5000 to 6000 RPM. What that suggests to me is that in order to take full advantage of the new motor, you may need to drop down an inch or two of pitch and it appears to have plenty of room to do so. That will improve the acceleration even more while allowing you to get the motor properly up in the top of the WOT range.
tedious posted 09-03-2015 09:45 AM ET (US)     Profile for tedious  Send Email to tedious     
Fish, I am not sure why you feel there was no increase in performance when you make reference to noticeably better acceleration earlier in your post. To me, that would be improved performance.

Can you clarify what prop you have on there? I think K just means that it fits an intermediate gearcase - is it aluminum or stainless?

In any event, it sounds like you need to do some testing to find a more appropriate prop, and you'll see even more performance improvement.

Phil T posted 09-03-2015 12:31 PM ET (US)     Profile for Phil T  Send Email to Phil T     
My F115 liked 3 holes up, 2 was best for all-around running.I would definitely move the motor up 1 more hole and re-test.

Is the VST outside of the intake manifold? That would be a great improvement.

FISHNFF posted 09-04-2015 01:58 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
Sorry. Acceleration better, but my mechanic did suggest synching the intakes. Thought that was for carbs, like on my old Mercaha 90. Said that would improve acceleration (on my old Yamaha). Never got the chance.

Top speed I thought would increase, due to the hype of more power, and the fact this block also makes 130hp. Guess acceleration is all I get.

I am currently running a Turbo 15"SS. I can get up to 6200 trimmed up, but no more than 32.5 knots, or 37mph.

The Yamaha prop is a K Black Stainless.

I was just hoping for a bit more out of this motor, but as the number on the cowl says on both, 115.

I'm getting the first service done, and will have it raised up on hole. Looks like quite a bit of spray coming up from the motor lower unit.


tedious posted 09-04-2015 08:30 AM ET (US)     Profile for tedious  Send Email to tedious     
Fish, 37MPH with a 115 doesn't seem all that bad to me.

However, for your Turbo, 6200 RPM, 2.15:1 lower unit ratio, 15 pitch, 37 MPH nets out to 9.67% slip using the propeller calculator here at CW. That's a very high slip number for the Turbo/Stiletto props - many times calculated slip numbers are negative.

I suspect that raising the motor is going to make quite a bit of difference - if you are going to stay using the Turbo, you might even want to move it up all the way.
Is there anything else that could be causing drag? How's the bottom (the boat's, not yours)?

The Turbo does seem like it's close to the right prop, from the RPMs you're hitting. You should gain some RPM from lifting the motor, possibly enough to make you want to go up in pitch if you're going to be frequently running trimmed out, looking for maximum speed. My F70 likes to be run hot, so I'm intentionally a tiny bit underpropped - more practical given that I am usually in conditions that preclude going all that fast.

Regarding syncing the intakes, from the parts diagrams the F115 only has a single throttle body, so there's only one butterfly and thus nothing to sync.


FISHNFF posted 09-05-2015 03:28 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
Yes Tim. The F115B has 1 throttle body. The previous F115 has 3.

The main point I am trying to make is that hanging a new Yamaha 115 4-stroke yielded no performance gains when replacing a 13 year old , older technology, smaller displacement motor.

37 isn't bad, but when the previous could due 39-40. Hmm. ..
And 37 is trimmed to the max.


Peter posted 09-05-2015 11:56 AM ET (US)     Profile for Peter  Send Email to Peter     
The advances they've made are incremental. So performance gains are going to be incremental.
tedious posted 09-10-2015 09:54 AM ET (US)     Profile for tedious  Send Email to tedious     
You should get the setup right before making any conclusions about overall performance. For example, if raising the motor gets the slip down to 5%, your speed will be almost 39 MPH, and at 0 slip, which is not unusual for Stiletto/Turbo, you'll be hitting almost 41.


jrp posted 09-10-2015 03:01 PM ET (US)     Profile for jrp  Send Email to jrp     
<Top speed I thought would increase, due to the hype of more power, and the fact this block also makes 130hp>

I am curious about your reference that "this block also make 130 HP." Can you tell me which model engine that would be? Thanks!

P.S. I also agree with these guys that the performance is respectable already and a few adjustments will likely improve it further.

FISHNFF posted 09-11-2015 03:51 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
My owners manual is for an F115 and F130

I was just comparing performance with previous F115.
If boat is constant, and top is the same, that performance is at least the same.
If motor has larger displacement, lighter, and claims being more powerful, then performance should be at least the same.

jrp posted 09-11-2015 07:07 AM ET (US)     Profile for jrp  Send Email to jrp     
Okay, thanks. I see now that the F130 is an engine available overseas, but apparently not in the North American market. Too bad -- it would be a good candidate for a 4-stroke re-power on the classic Outrage 18/19 hulls like ours.

Info about the F130 from the Yamaha Australia website:

tedious posted 09-11-2015 08:28 AM ET (US)     Profile for tedious  Send Email to tedious     
Where do you see the claim that the F115B is more powerful than the previous version?
jrp posted 09-11-2015 08:52 AM ET (US)     Profile for jrp  Send Email to jrp     
The "B" version has increased displacement and is lighter than the previous "A" version. So at a minimum, it should have a better power-to-weight ratio.
tedious posted 09-11-2015 10:44 AM ET (US)     Profile for tedious  Send Email to tedious     
Yes, if it weighs less and has the same power, the ratio will be improved. However, I am interested in finding out about the source of the claim that the F115B puts out more power than the previous F115.


jrp posted 09-11-2015 10:55 AM ET (US)     Profile for jrp  Send Email to jrp     
Well, among other things, Yamaha USA has this (quoted below) to say about the 115B. Note the assertion of "more power and better mid-range torque":

"Best Power-to-Weight Ratio

"With 1.8L displacement and weighing just 377 pounds*, the Yamaha F115 In-Line Four is not just the lightest 115hp DOHC four stroke on the water; it’s 24 pounds lighter than it’s closest competitor. Twenty four pounds. How’s that for class-leading power-to-weight?

"Incredible Power

"The new F115 features increased displacement, now measuring 1.8L. Its DOHC four-cylinder design features larger intake and exhaust valves for easier breathing, more power and better midrange torque. Additionally, the higher full-throttle RPM range; 5,300 – 6,300; helps maintain top speed while allowing use of lower-pitch propellers for better hole shot and acceleration.

"Faster Acceleration

"The new F115 has it all—including knock sensors—unheard of in this class of outboard. That protects the new F115 from low-octane fuels and allows it to operate constantly at peak output. The result is a zero-to-200-foot time that’s 0.7 seconds faster than our previous 115 model."


jrp posted 09-11-2015 11:00 AM ET (US)     Profile for jrp  Send Email to jrp     
Also note the qualifiers used to describe the weight of the engine. This 115B, as light as it is, is still heavier than the new Mercury 2.1L 115 FourStroke. But the Mercury only has a single overhead cam, so Yamaha can make their "lightest 115hp DOHC four stroke" claim with a straight face.
tedious posted 09-11-2015 12:55 PM ET (US)     Profile for tedious  Send Email to tedious     
Thanks, that's what I was looking for - and here's a link to make it easy for others to find:

I don't read that as a claim that the F115B makes more power than the previous F115 (it's more generic marketing hype, which all manufacturers indulge in) but I can see how someone might interpret it that way.

Now back to getting FISHNFF's performance where it should be - any luck with getting the motor raised? Based on my experience with my F70, I have my doubts that the Turbo is the right prop, but might as well get the height right first as it does not cost anything.

FISHNFF posted 09-12-2015 02:12 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
No new information on the motor, except the oil drain plug is nicely located center, below the rear exhaust ports, with a rubber spout. It drains right into an empty one-gallon container.

The oil filter is now the same as an F150 and is smaller. It faces down on the port side with a catch shield.

All cables and hoses, including trim switch, are on the port side.

There is a single-ram tilt and trim.

The spark plugs are NGK LFR6E--only! No cross reference, and no local shop has them in stock. The list price is $30 each. I seldom changed plugs on my previous Mecury-branded Yamaha or F115. So clean. These looked perfect too.

I dropped the boat off at Outboard Motor Shop this morning. The Do-List includes raising motor an additional hole; fix trim gauge; check loose oil dip stick; tighten throttle friction; bleed hydraulic steering.

I saw a big gelcoat chip in keel, and I discovered crack in underlaying glass with water dripping. This damage happened within last couple months. A repair guy will cut open, dry with heater fans, and patch for $450.


jimh posted 09-12-2015 06:58 AM ET (US)     Profile for jimh  Send Email to jimh     
It is hard for a human to have quantitative memory of sound levels for long periods. To judge two sound levels to be the same when you are exposed to them with a separation of many months is probably not going to be very accurate. In order to assess the sound levels of the two engines, you would need to be able to compare them at the same time, with not more than about ten seconds of interval between the exposure to the sounds. Humans just cannot remember sound levels with any accuracy for very long.
tedious posted 09-12-2015 01:45 PM ET (US)     Profile for tedious  Send Email to tedious     
Bummer on the crack and water intrusion - I guess you figured out where the 2 MPH went! Hopefully the repair will come out nice.

Thanks for the into on the motor - the oil drain design sounds great! I don't replace my plugs every year, but rather just clean and regap them. Probably they'll be available online for a lot less by the time you need them.

Phil T posted 09-12-2015 02:08 PM ET (US)     Profile for Phil T  Send Email to Phil T     
I think your lower performance is due to the prop choice. Raising the motor gave me 150 rpm's for each hole.

Maybe a Yamaha 15 pitch to gain RPM?

Do you run heavy alot ? Maybe a different brand is better suited.

FISHNFF posted 09-16-2015 01:06 PM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
I don't have an accurate way of measuring actual sound level, just "seat of pants" feeling based on me using my boat. I understand factors like wind make a big difference. For tears with a 2 strike we would adjust trolling speed by the sound of the motor, keeping my eyes on the water around me and the lines in the water. Unless it's absolutely calm, that's out the door.

I have also purchase and used a 15" Turbo SS. It gets me 6200RPM trimmed up, but where I like to run is 4800-5000, a bit high. I'm hoping raiding the motor will help. The crack is kinda recent, so most of my performance experience is pre-crack.

Mileage numbers so far are about the same. No long trips (over 30 miles) to really guage.

Will check back in later!


vin1722or posted 09-16-2015 03:51 PM ET (US)     Profile for vin1722or  Send Email to vin1722or     
I just ran a [Yamaha F115XB] on my 1981 OUTRAGE 18 with one person and a half-full fuel [tank]. [The boat speed was] 41-MPH [at an engine speed of] 6100-RPM at wide-open-throttle. [The propeller is] a black, painted, Yamaha 13 x 17 steel propeller.

I [tried] a performance, three [blade?], Yamaha propeller of dimensions 13-1/4 x 16, and only got [an engine speed of] 5,900-RPM at wide-open-throttle. The boat still ran at 40-MPH. The engine [is described as being mounted at what sound like one-hole up.] I may next try a TURBO 13-1/4 x 15. [Give me] any thoughts [you have about this data].

jimh posted 09-16-2015 06:08 PM ET (US)     Profile for jimh  Send Email to jimh     
If the recommended engine speed range at full throttle of the Yamaha F115XB is (as cited by Peter above to be) 5,300 to 6,300-RPM. then, when you report that you obtained wide-open-throttle engine speeds with your Yamaha F115B of 5,900-RPM and 6,100-RPM, my thoughts are that you are right in the range specified by Yamaha, and you are in the upper part of that range. That is good.

A boat speed of 40-MPH or 41-MPH on a Boston Whaler OUTRAGE 18 with only 115-HP sounds very good, to me.

tedious posted 09-16-2015 11:18 PM ET (US)     Profile for tedious  Send Email to tedious     
Vin, I have the Stiletto version of the Turbo you mention for sale - drop me a note if you are interested.


tedious posted 09-17-2015 08:22 AM ET (US)     Profile for tedious  Send Email to tedious     
Fish, can you please clarify the following phrase?

"where I like to run is 4800-5000, a bit high"

Are you saying that at the speed you typically like to run at, the motor is turning at 4800-5000, which you consider to be too high a motor speed?


FISHNFF posted 09-17-2015 05:10 PM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
It seems like I need to run the engine at a higher RPM to cruise at the same speed as with the previous motor. Just my feeling.

According to the specs, the gear ratio is the same at 2:15 to 1, so the same prop at the same RPM should result in the same speed. Just doesn't feel the same. It feels like the motor must work harder to achieve the same speed.

I ran this boat with 3 aboard with bait tank and big cooler full, as well as alone with nothing. Acceleration feels stronger at all load levels than previous, just doesn't seem as fast for said loads.

I read posts about this motor and I guess it's about right, I'm just basing my new experience with this motor against the same hull with the older F115.


tedious posted 09-18-2015 08:31 AM ET (US)     Profile for tedious  Send Email to tedious     
Got it, thanks for the clarification.

As I previously posted, your slip figure is off the charts (high) at almost 10% - most users of Turbo 1 / Stiletto Advantage props have calculated slips that are negative. That means something funny is going on - you're putting energy into pushing water that somehow isn't contributing to driving the boat forward. That is likely due to a combination of the low motor mounting height and the hull damage you discovered.

Assuming you did not have 10% slip with the previous setup, I'm sure it does feel like you're having to turn more RPM to achieve an equivalent speed. I think you're going to see quite a difference when you raise the motor and repair the hull.

With that said, after quite a bit of experimentation, I found that the large, grippy Stiletto was a poor match for the power curve of the F70 on my 15. Since the F115B has the same 6300 RPM redline, I am thinking it may have similar characteristics - makes its power a little higher up in the RPM range than 2-strokes and older 4-strokes. So after you get your repairs done, you still may want to try a prop that spins up easier - it made a huge difference to my satisfaction with the F70.


Peter posted 09-18-2015 09:26 AM ET (US)     Profile for Peter  Send Email to Peter     
Given that the F115B has a WOT range of 5300 to 6300 RPM versus the old F115 range of 5000 to 6000 RPM, I think you can expect that the motor's power curve is different throughout the entire operating range and that is possible that at 4000 RPM, for example, the new F115B is not making the same power as the old and they will feel different if running with the same propeller. That 0 to 115 HP output range is now spread out over 6300 RPM rather than 6000 RPM.
Qtrmeg posted 09-19-2015 11:15 AM ET (US)     Profile for Qtrmeg  Send Email to Qtrmeg     
New engines take some time to break in and loosen up. Your new engine hasn't reached it's full strength & power yet, not to mention economy.

I think it is encouraging that you feel the new engine is stronger at all speeds now.

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