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Author Topic:   1987 CENTER CONSOLE 15
JP3 posted 07-14-2015 08:35 AM ET (US)   Profile for JP3   Send Email to JP3  
I am going to replace [the outboard engine on a 1987 Boston Whaler CENTER CONSOLE 15] with a new Mercury 60-HP Command Thrust FOURSTROKE with a 2.33 gear case. The propeller on the current motor is a 12.7 X 19 four-blade. I doubt the current prop would be suitable. What prop would you recommend?

A rod and crankshaft bearing went bad in my current engine, a 1987 Mercury 70-HP with a 2.3 gear case.

tedious posted 07-14-2015 09:10 AM ET (US)     Profile for tedious  Send Email to tedious     
JP, I am curious as to why you are going with the Command Thrust rather than the regular 60.


Jefecinco posted 07-14-2015 09:54 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
The horsepower is probably going to be very close with the new engine due to age (wear) and to rating criteria in 1987 compared to 2015. The gear ratio is also very close. I would try the same propeller before looking for a replacement assuming you've been happy with the performance. Differences in weight and lower unit shape may make a significant difference but a test run or so with the new engine and old propeller will determine that.

I don't know what year outboard engine power rating criteria changed so I could be very wrong in my assumption that the power of the two engines will be very close.


JP3 posted 07-14-2015 10:09 AM ET (US)     Profile for JP3  Send Email to JP3     
I really don't like the way the 4-strokes reach their powerband. That's just a function of the way the 2 vs 4 stokes.

Based on the research I've done so far, I should be able to get the boat on plane quicker. The larger gear - 2.33 nearly matches the motor I am removing.

When deciding on power, you always want the maximum possible HP. I'd like to get a 70. The only offerings are the Yamaha 70 and the Suzuki 70. The Suzuki is too heavy and the Yamaha is too expensive. Evinrude has a 65 HP but it is really heavy and requires a Tech to sign off on the installation. (I plan on reusing as much of the existing rigging as possible - so the Mercury 60 HP CT is the best option for me that I have found so far.)

The 60 hp Command Thrust matches the acceleration and fuel efficiency of our competitor’s more expensive 70 hp outboard model."

Hopefully, all of the performance matches the Mercury advertising.

Tom W Clark posted 07-14-2015 10:22 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The Mercury 60 Command Thrust is an excellent choice for the Sport 15.

I recommend a 13-1/4" x 17" Stiletto Advantage or Turbo 1, though these *might* be too much pitch

A 13-1/4" x 16" Yamaha Performance Series 3-Blade might be an even better fit

tedious posted 07-14-2015 01:04 PM ET (US)     Profile for tedious  Send Email to tedious     
JP, I mention the smaller gearcase motor based on my experience with the F70 on my 15, turning a Stiletto Advantage 1. In general, I really like the setup - good performance and prop grip, and super mileage. But I am wondering if the large, low-slip prop is really the best choice for a 15 running a 4-stroke that makes its power mostly at the high end of the RPM range.

I tried both 13-pitch and 15-pitch Stilettos, before settling in on the 15 for regular use. The 13 would let me run up to redline at 6300 RPM pretty readily, with some trim, even with a moderate load. The 15-pitch tops out at around 6000, with a light load, on flat water and trimmed as much as I'm comfortable with. But once you add a load, you really can't get higher than about 56-5800 RPM. Maybe the 14-pitch version of the prop (Yamaha-branded, thus a lot more $$) would be the best. But just going on my gut, and not being an expert, I'm thinking that a prop with smaller blade area might allow more slip in the midrange when loaded, let the RPMs spin up and then make use of the additional power once up at the top end. That probably flies in the face of conventional prop wisdom, but I feel like it's worth a try.

One other note is that I thought the changeover from powerhead to prop shaft horsepower ratings was in 1986 - at least I think that's when OMC bumped up the displacement on the 60/70 triple. The bottom line is I am not sure whether your current motor is powerhead or propshaft rated.


mkelly posted 07-16-2015 03:08 PM ET (US)     Profile for mkelly  Send Email to mkelly     
Coming late to the conversation but why not the 60 HP E-TEC. I have the same 15' CC model & my brother gifted it a new Yamaha F60--it's fantastic but we also have a 200 HP E-TEC on the bigger boat and it is just fantastic. Might give you the torque you are speaking of. E-TEC guys who have the mid range in line models speak up. Our 200 HP trolls all day, doesn't spit a bit, and purrs like a four stroke. I love it
emaier posted 07-24-2015 08:35 PM ET (US)     Profile for emaier    
I just repowered an '85 Center Console 15' with a 60 E-Tec. Overall, I'm happy with with it. With a Stiletto Advantage 1 19" prop, two persons, 6 gals of fuel, two batteries in the console and a trolling motor up front, I can turn almost 6000 RPMs and close to 40MPH. Loaded down with a couple more people, 6 more gallons of fuel and misc gear, I can still turn close to 5600 RPMs (I didn't check the speed, but it was fast enough).

The only thing lacking is hole shot, especially heavily loaded or skiing/wakeboarding. Even with the vent holes in the Stiletto, the prop has very good grip and fast starts do not induce any slip to allow the engine to spool up into the better part of the torque curve. I'm considering getting a second prop with less pitch, smaller diameter and possibly with 4 blades for "heavy" or watersport days.

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