A lot of people ask, "How fast would/should my boat go with this prop?" Of course this is a tough question to answer. It all depends on motor HP, boat weight, boat type and load.

I have made this excel spread sheet that will give you a good guess as to what to expect.

You will need IE to view it.

http://home.comcast.net/~team_dougherty/prop.htm

Just enter your prop pitch, engine rpm and gear ratio. Enter 2.5 for 2.5:1, enter 2 for 2:1 etc...

You will then get the approximate boat speed with that prop.

But do not think that just upgrading to a bigger prop you will gain speed. Your motor might not have enough power to turn the bigger prop at it's max RPM.

For example, my boat goes faster with an 11 than a 13 with my wife and son on board.

If I am by myself the 13 one gives a better top end speed but a slower hole shot.

If any one has any suggestions to improve this let me know.

Paul

Thanks man. I'll have to give this a shot on my boats. I do have one question though. How do you figure out the pitch of your prop? This is probably a dumb question but I've never had the need to know the pitch.

fishinfool,

It should be stamped onto the prop somewhere on the hub. It is usually part of the part number. Just do a google search on the part number and manufacture name. You should find the pitch somewhere.

Paul

There are several excellent prop calc programs. They will only give you an estimate though, they have no way of knowing the slip factor.  They will let you calculate the slip.   All props slip, this can be anywhere from 5% - 35%, the amount of slip varies actual speed greatly and is affected by hull design, engine setup and prop type. Calculating the slip and making changes to the setup to reduce slip is a way to get more speed.

There are several excellent prop calc programs. They will only give you an estimate though, they have no way of knowing the slip factor. They will let you calculate the slip. All props slip, this can be anywhere from 5% - 35%, the amount of slip varies actual speed greatly and is affected by hull design, engine setup and prop type. Calculating the slip and making changes to the setup to reduce slip is a way to get more speed.

Slip used to be a big problem with my boat.After getting the plate set correctly,I gained alot more speed.When I first bought the boat,I was in the 35% slip group.