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Author Topic:   Montauk 170, Optimax 115 Pro XS
Ridge Runner posted 05-23-2010 11:23 AM ET (US)   Profile for Ridge Runner   Send Email to Ridge Runner  
[On a Boston Whaler 170 MONTAUK, a Mercury] Optimax 115 Pro XS, [on its] first run after break-in, [with a] Mercury Black Max 21-[pitch] propeller, [produced an engine speed of] 5,400 RPM [and a boat speed of] 48.3 MPH. Comparing the engine to my E-Tec 115 H.O., the E-TEC is smoother than the Optimax. The OptiMax has a vibration at 1,300-RPM that makes the Montauk 170’s bow rail vibrate fiercely. The E-TEC has a nicer idle sound, but at cruise both are pleasant sounding. I do think the OptiMax needs a 19-pitch prop. Once the prop is dialed in for the OptiMax I really think both engines will perform very close to each other, with very similar top ends and the E-TEC having an advantage in acceleration.

I think Mercury did a nice job with the cowling design and graphics on this motor, much nicer than the old Mercury designs. This would be a perfect Brunswick boat and motor combination for Boston Whaler to offer, if they every raise the horsepower rating. I do not feel this boat is over-powered, and, after running this boat with a 90-HP, all I can say is this 115-combo really has some great mid-range guts. Both 115-HP boats have sweet spots around 4,000-RPM and 32-MPH. I will post comparative pictures, performance, and fuel burn numbers once the OptiMax is dialed in.

jimh posted 05-23-2010 01:19 PM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for the information on the use of a Mercury OptiMax Pro XS 115-HP motor on the Boston Whaler 170 MONTAUK.

As for the prospects of Boston Whaler offering this combination as a factory installed option, my impression is they would be unlikely to do so. When Boston Whaler offered Mercury OptiMax engines as optional power choices on their boats, the customers of Boston Whaler did not choose those OptiMax engine options with much frequency. The percentage of Boston Whaler boats sold with Mercury OptiMax motors when the OptiMax was a factory option was extremely low, in the neighborhood of only a few percentage of boats sold. For that reason, I believe that Boston Whaler decided to drop the OptiMax as an option, and instead transitioned to Mercury FOURSTROKE motors and Mercury VERADO motors for factory rigged options. It was not economical or practical for Boston Whaler to have OptiMax motors on-hand to fill orders when the orders were so infrequent.

For a re-power option, it sounds like the Mercury OptiMax Pro XS 115-HP motor may be a good choice, particularly because I believe that the existing control rigging, engine harness rigging, engine gauges, and so on, from the original Mercury motor will be easily adapted to a Mercury OptiMax Pro XS replacement motor.

Ridge Runner posted 05-23-2010 08:31 PM ET (US)     Profile for Ridge Runner  Send Email to Ridge Runner     
Here are a cuple of pictures: 2002%20%20Montauk%20170/
L H G posted 05-24-2010 02:47 AM ET (US)     Profile for L H G    
A boat that will run 49 MPH should not be using an aluminum prop. Generally aluminums are tapped out on rigs that will do around 35 MPH top end, and lose performance over 40 MPH.

I would install a 20" Laser II, and raise the engine another bolt hole. The boat should do over 50. Considering the boat has bottom paint, only 3 cylinders and fewer cubes, the Merc sounds really strong. Opti's are known for the quickest mid-range acceleration response. I'll bet the Optimax gets 15% better fuel economy at cruise. I would have a servicing dealer look at the rough spot. Not normal.

The photos look nice.

jimh posted 05-24-2010 10:55 PM ET (US)     Profile for jimh  Send Email to jimh     
Larry--Just curious where you are getting your comparative data for the E-TEC and OptiMax in regard to their fuel economy? On what boats have you run both an E-TEC and OptiMax? What fuel flow meaurement data have you collected?
Peter posted 05-25-2010 07:52 AM ET (US)     Profile for Peter  Send Email to Peter     
The report here seems to match up well with the side by side video comparison of the E-TEC 115 and Optimax 115 I referenced in an earlier thread. See . With greater displacement and an additional cylinder, the E-TEC 115 will have a smoother running quality and will have more mid-range punch.

sosmerc posted 05-29-2010 11:21 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
AFter you get some time on it, you will need to try some props. I'll bet you could run 3 holes up as well.....especially with props like the HIghFive, Laser II, etc.
Don't forget to run the FloTorq does make a difference with regards to clutch chatter.
Your "shudder" or Vibration could be the prop. Not all props are created equal....some are junk out of the box. Or someone may not have properly installed the prop. I worked on a boat today that had a pretty new looking prop on it......BUT, they left off the forward thrust washer. The prop was slowly chewing it's way into the gearcase.
Have fun!
Ridge Runner posted 06-03-2010 09:30 AM ET (US)     Profile for Ridge Runner  Send Email to Ridge Runner     
I bought Dave's Stiletto Advantage 1 19" pitch prop, so we will see how it runs with that. The "shudder" from the outboard isn't anything that I wouldn't expect from an inline 3, I think it is just at the prefect mechanical resonance for the bow rail at 1,300-RPM.
jimh posted 06-05-2010 08:54 AM ET (US)     Profile for jimh  Send Email to jimh     
Regarding the vibration of the bow rail and motor at a particular engine speed, I tend to agree with the interpretation that this is just a normal occurrence where the propeller, the motor, the engine mount, the hull, and the rail all have some resonance, and the result is some vibration.

The suggestion from L H G that the vibration represents a defect in the brand new Mercury OptiMax 115 Pro XS motor which need to be repaired seems much less likely. However, L H G may have extensive first-hand experience with these just-new-to-market Mercury motors and may have knowledge about their operating characteristics. On the other hand, I have absolutely no first-hand experience with a Mercury Optimax 115 Pro XS motor, but I would be very surprised to find that a brand-new Mercury motor was delivered with a defect that caused it to vibrate at a certain speed.

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