Prop Recomendation

[Badger13]

Hello,

I just recently purchased a used Glasstron SX 175. I am a newbie but been reading and learning as I go. I took the boat out for a test run this weekend and noticed the boat runs WOT at around 5,000 RPM. I didn't get to GPS the speed so I don't know what speed I topped out at (i'm guessing 35ish?. The prop on the boat is a 17p. I have the 3.0 alpha 2 drive. Mercury prop selector says I should be running 21 to 23 Pitch and calculated top speed of 43. Looking for some opinions or real world results. Any other recommendations? My boating will be a good mixture of cruising and wake boarding. I would like to find something that gives me decent top speed but still can get on plane.

 

[TexMonty]

The experts here will want to know GPS speed to really tell you anything. Also how loaded was your boat? 21/23 pitch is pretty high for a 3.0. I have learned it makes quite a bit of difference between 2 and 6 people in my boat as far as speed/rpm.

 

[alldodge]

Hello,

I just recently purchased a used Glasstron SX 175. I am a newbie but been reading and learning as I go. I took the boat out for a test run this weekend and noticed the boat runs WOT at around 5,000 RPM. I didn't get to GPS the speed so I don't know what speed I topped out at (i'm guessing 35ish?. The prop on the boat is a 17p. I have the 3.0 alpha 2 drive. Mercury prop selector says I should be running 21 to 23 Pitch and calculated top speed of 43. Looking for some opinions or real world results. Any other recommendations? My boating will be a good mixture of cruising and wake boarding. I would like to find something that gives me decent top speed but still can get on plane.

:welcome: to iboats

Turning a 3.0 at 5K rpm's is good, so your in your range. Increasing the pitch from 17 to 21 and 23 will only reduce your WOT rpm. While the normal would have a 21 to 23 pitch prop turning your same rpm, the drive ratio makes the difference. My guess is your running on the correct range for boat and motor.

As Tex mentioned. where going to need and accurate speed (gps) and rpm (tach)

 

[Badger13]

Thanks guys. I will be back out this weekend so I will bring the GPS and get a better Tach reading. Just knew the motor said max RPM range was 4800 and then saw the prop recommendations so it got me thinking maybe I have the wrong prop! I read about people getting to 40 mph with their 3.0 and still pulling skiers so I would like to shoot for a prop that could be a nice balance.

 

[Badger13]

I was able to get out again tonight and got a better reading on tach and speed. I was at 5200 RPM's and topped out at 39mph. (Motor trimmed 1/2 way up). Let me know if that helps.

 

[steelespike]

Your numbers are just about perfect for a 3.0 in a boat about 18 ft. A 17 is usually suggested for a load of people with water sports.
With the proviso it will over rev with a light load.If you want better top end you will need a 19 or 21" prop.
When you increase pitch you lose power, like a car goes faster in high gear but may struggle on a tough hill.
Using the rule of thumb 150-200 rpm per inch of pitch change a 19" prop "COULD" get you to about 4800 rpm.
But a little less power and maybe more top end.You might get to 40.
It is important the motor is able to rev freely within its wot rpm rating.
If you often run with a boat load of people you may want to stick with the 17 and not exceed 4800 with a light load.

 

[Badger13]

thanks steelespike! So far the prop has been fine for my needs. I rarely get to go too fast, mostly pulling wakeboarders and cruising so I may just stay where I am at. Seems to get on plane very easily. If I buy a spare I may get a 19...

 

[steelespike]

Just want you to understand its not good to run over the 4800.max recommended.5200 is looking for trouble.

 

[Badger13]

Yep understood, thanks again.