Top speed?

[Tuckerboy1]

I have a 2002 glastron SX175 with the mercury 3.0 and alpha one outdrive and I was wondering what the top speed should be on this boat. I am getting about 33MPH . The prop is beat up pretty good so any recommendations on a new one. Stock or upgraded one.

 

[itsathepete]

Top speed is a function of engine rpm, gear ratio, prop pitch, and prop slip. To determine theoretical max speed enter your actual WOT rpm, drive gear ratio, and prop pitch into any online prop speed calculator. Set prop slip to zero. Set prop slip to 10 or 15 to estimate real world top speed. A damaged prop will increase slip and reduce top speed. Adjust prop slip numbers until your measured top speed is matched and you will have an idea of how bad your prop is. You need an accurate tach and gps speed measurement for this to work

 

[QBhoy]

You should be able to achieve 40 mph gps or a little more, with a good prop.

 

[Scott Danforth]

Fix your prop

 

[achris]

I have a 2002 glastron SX175 with the mercury 3.0 and alpha one outdrive and I was wondering what the top speed should be on this boat. I am getting about 33MPH . The prop is beat up pretty good so any recommendations on a new one. Stock or upgraded one.

Given the boat and the engine, 30 knots seems about right. Certainly a banged up prop isn't going to help.

As for a replacement prop, depends on what you use the boat for. Also, the 3 litre engine's not a speed demon. I doubt you'd get much benefit from a 'performance' prop. If you want more stern lift, then think about a 4 blade (knowing that you'll drop a few knots at the top end), or even a 5 blade for skiing and towing toys around. For flat out speed, if you can find a 2 blade, that's the go, but they have a lot of negatives along the way...

There's no 'one size fits all' as far as props go. It's very much a fact of props that while any prop will be great at what it's designed for, it's likely to be pretty bad at other things. Consider how you use the boat most of the time and prop for that... Or have multiple props that you just swap in and out of as required.

Chris.....

 

[jimmbo]

I think Glastron had in it's little Salesman book that the SX175 would do around 42 with the 3 liter. I used to have a couple of copies of those books, but I can't find them.

 

[Tuckerboy1]

Given the boat and the engine, 30 knots seems about right. Certainly a banged up prop isn't going to help.

As for a replacement prop, depends on what you use the boat for. Also, the 3 litre engine's not a speed demon. I doubt you'd get much benefit from a 'performance' prop. If you want more stern lift, then think about a 4 blade (knowing that you'll drop a few knots at the top end), or even a 5 blade for skiing and towing toys around. For flat out speed, if you can find a 2 blade, that's the go, but they have a lot of negatives along the way...

There's no 'one size fits all' as far as props go. It's very much a fact of props that while any prop will be great at what it's designed for, it's likely to be pretty bad at other things. Consider how you use the boat most of the time and prop for that... Or have multiple props that you just swap in and out of as required.

Chris.....

You have been most helpful. I do use the boat mostly to tow tubes . So top speed is not as important as being able to keep steady speed

 

[Tuckerboy1]

Top speed is a function of engine rpm, gear ratio, prop pitch, and prop slip. To determine theoretical max speed enter your actual WOT rpm, drive gear ratio, and prop pitch into any online prop speed calculator. Set prop slip to zero. Set prop slip to 10 or 15 to estimate real world top speed. A damaged prop will increase slip and reduce top speed. Adjust prop slip numbers until your measured top speed is matched and you will have an idea of how bad your prop is. You need an accurate tach and gps speed measurement for this to work

I will do this once we get tach to work thank you

 

[Rick Stephens]

You have been most helpful. I do use the boat mostly to tow tubes . So top speed is not as important as being able to keep steady speed

When I was running a 17 foot with the 3.0L motor I ran a 15 pitch 4 blade Solas wheel. That gave me more jump out of the hole when pulling skiers and boards. Just had to watch the top end that I didn't over-rev.

 

[Scott Danforth]

on my 16 foot boat with a 3 liter. I carried 3 props. a 19P for WOT running, a 17P for general use and a 15P for water sports and trolling

 

[Scott06]

When I was running a 17 foot with the 3.0L motor I ran a 15 pitch 4 blade Solas wheel. That gave me more jump out of the hole when pulling skiers and boards. Just had to watch the top end that I didn't over-rev.

Agreed - also had a 17 ft with 3.0 used a 16" 4 blade for skiing , 18" 4 blade for general use.

To op I would repair the prop you have on it or get similar to get a baseline on performance and WOT rpm before experimenting with props. Most shops are like $80-100 to repair a 3 blade AL prop