Opinion Needed: Horsepower for 175

[CTsalt12]

Hi All,

Here's the deal.  I have a hell of a deal on a brand new Merc 4 stroke 90, and I have been looking to re-power.  But-I'm wondering if 90 is too little power.  I have a worn out 115 on my boat now.  I don't get much over 32 mph at 5000 rpms, so I'm used to fairly slow speeds.  However, I'd like more speed of course. 

The boat has added weight of a trolling motor and 2 batteries up front.  I haven't had to raise the waterline, so don't think I've absorbed much water.  I usually fish with 1 or 2 other guys + gear, and I pull people wakeboarding about 2x a year.  The new engine would be about the same weight as the old one actually (roughly 360 lbs)

I don't need to go 60 mph, but I'd like to cruise at 33 on flat days, and be able to get on plane easily.

What do you guys think?  Should I pull the trigger?  Enough power?  Or wait for a 115?

[mshugg]

I had a 1985 170 that was powered with an OMC 90.  I thought is was perfect power for the boat.

The four stroke weighs more at 359 v 302 for my old Johnson, but I think it should be fine.

[RickK]

I agree with Mshugg - the 90 or 115 (usually same engine with carb changes) 2 strokes are perfect for the boat.

[wingtime]

I have an Evinrude 90 hp Ocean pro 60 degree eagle block on my 170. More than. Enough power. Hole shot puts the bow in the sky... 38mph+ wot. I would not want much more power or weight on it.

[boatnamesue]

I have a 115hp on my 170...couldn't be happier with the boats performance.  If you are wanting more speed then the decision between 90 and 115 is an easy one, since you've already experienced max hp with a worn out 115hp.  It's a good thing you don't need to max out at 60mph cause you won't get it from a 115hp anyway.  But cruising in the mid 30's at 3/4 throttle is a sure thing.  I top out at 46mph @ WOT (5400 rpm).

[CTsalt12]

Thanks all.  I was being sarcastic about the 60 mph. In reality, I don't need to realistically go above 40 ever, and even then I would only go that speed in very few days when weather permits and I just feel like testing the boat.  In the sound I run in, it's always choppy and even mid 30s is uncomfortable a lot of the time.

[wingtime]

That is the reality about boats.  Certain designs are gonna have a sweet spot where they ride and perform the best.  This has nothing to do with horse power. To be honest I would not want to go any faster on my 170.  I'm sure a different prop would get me over 40, but I rarely run around at WOT so why bother going any faster.  Mine cruises best at 25-30 mph.

[larsli68]

I have a 115 Merc OptiMax on my Aquasport 170. I have moved the scuppers up 3/4 of an inch. Works really good with a 19" Spitfire prop.

//Lars

[CTsalt12]

Hi All.  Wanted to share some results of the new engine.  2016 Mercury 90 HP 4 stroke, boy is she quiet and smooth.  At idle you really can't hear the engine running.  I have been testing with the prop from my old engine, 19 pitch.  It only gets up to 4500 RPMs, and hits 35 mph at that speed.  Clearly I need to drop down in pitch, so I have a 16 pitch 13.25" on the way, which I will be testing this weekend.  Should be fun!

Also found out from the engine buyer that it had good compression on all 4 cylinders, interesting if you know about my engine woes.

[CTsalt12]

One more performance update.  I have the new prop on.  I now get up to 5500+ RPMs, if my memory serves and it runs really nice at that speed actually.  Getting up to about 37 MPH, plenty of speed, burning 8 GPH.  At 4000 RPMs getting 30 mph and cruising around 5 GPH, or 6 miles per gallon.  Making it about 3x more efficient than the old 2 smoke.  Nice : ) Did my first long cruise across the long island sounds last weekend and I was really pleased on all accounts.  Pics will follow soon

[wingtime]

Those sound like really good numbers for that hull.  I can squeak 38 or so out of my 170 with the 90HP Ocean Pro.  More than fast enough.

How is the weight difference and where are the scuppers sitting in relation to the water line?

[CTsalt12]

There is no significant weight difference between the old Mercury 2 stroke 115 and the 2016 Four Stroke 115 or 90.  The Merc 4 strokes are crazy light.  May have been 20 pounds? I don't recall exact numbers.  Scuppers are an inch out of the water without anyone in it full tank of gas.  If Im standing alone in the back I get a little bit of water hardly noticeable, 2 guys in the back and expectedly  get more.  Same as always since I've had this boat.  I don't believe it's gained any weight in my 7 years.