175hp Mercury O/B Question

[jwilkes]

I have 2 general questions. What is the correct wide open RPM range for my motor, and is the prop I'm using correct.

I have a 1993 Trophy 2003CC center console boat with a 175hp Mercury outboard motor. I cross referenced the number on the original prop, and it was a 14x19- aluminum of course. The boat performed average I would say, and would do 47-48mph on the speedo @ about 57-5800rpm's, with 2 people, lighter load, and half-tank of gas(around 40 gallons). I asked around for advise online, and most everyone reccomended to go with a 3-blade SS prop with the same diameter and pitch(I wanted to keep my original prop as spare, and more performance all-around.) I use my boat for all-around purposes...tubing, cruising, fishing...blah blah blah. I decided on a Michigan Wheel Apollo XHS SS prop, 14 1/8 x 19 pitch. Fit on great. Noticably more rake and geometry to this prop. Pulls up out of the water and gets on plane MUCH smoother and faster now, and runs smoother thru the water. Same top speed, but DROPPED the rpms to around 5200+/-. I attribute this to my aluminum prop having flex under load, and new geometry of the SS prop.

I am overall happy with the performance, but is the lowering of the rpms going to cause a problem? Any input is appreciated!!

Thanks!

 

[Crownie2]

Re: 175hp Mercury O/B Question

Your speed looks a little high, but that could just be the speedo.

According to Merc (prop calculator), you should be able to pull a 19" at sea level.

Maybe there are other things about the boat (weight, hull condition, etc.) that are pulling it down.

I'm not really sure of the recommended rpm's of that motor but my 175 liked to run up to about 5,800.

 

[jimmbo]

Re: 175hp Mercury O/B Question

Rpms are still in the rpm range, 5000 - 5500. The drop in rpm is likely due to the SS have a much better grip on the water and not slipping as much, not the the Aluminium prop flexing.
Has the engine been raised on transom so the ventilation plate is higher than the bottom of the boat? If not, raising it an inch or two will reduce drag, raise rpm a 100 - 200, raise top speed, plus improve handling.