How fast should I go?

[Glastron175]

No answer before so I'll try again. My boat is a Glastron 175SF with the 3.0GSMEFS engine. At WOT it goes 36 MPH and 4600 RPM. I have a new 19 pitch 3 blade prop. Is this performance as it should be? I was hoping for a little more speed. And should the RPM go higher?

 

[bitterboater]

Re: How fast should I go?

Just remember that, speed kills.

Your likely doing about what the boat should be doing.

 

[unclefester32]

Re: How fast should I go?

2 things I'd ask: is the boat all the way trimed out? And what prop was on it b4 the new 1......if same dia. I'd try a prop with more pitch. It should have np turning a 21 pitch. That's just my 2 cents worth....BTW is the new prop aluminum or stainless?

 

[honeys money]

Re: How fast should I go?

My Larson, with a 3.0 runs about 45, on GPS, 23" pitch prop by myself, 43 with 19".

 

[jigngrub]

Re: How fast should I go?

Lots of variables. Were you using a GPS? How many people and how much equipment did you have in the boat? Going against the current or wind? Is your hull clean? Are you hauling around a bunch of waterlogged foam in the bottom of your boat?

My 17' deep V tinny does 32.9 mph with a 50 hp 4 stroke and stock prop with just me in the boat on a calm day with no current.

 

[Maclin]

Re: How fast should I go?

The rpm is about right I think. The drive ratio makes a big difference in what speed you get from any given prop. With 15% slip factored in your drive ratio calcs to about 2.0

With a 21 pitch prop you would get 38mph if the same rpm can be reached. The higher the pitch the more HP you need to hit the same rpm.

To be accurate in any prop calculations though, you need to know the drive ratio, accurate speed and accurate rpm achieved at WOT.

Here is a link to a basic prop calculator....:
http://www.rbbi.com/folders/prop/propcalc.htm