Duoprop sizing

[gluttonforpunishment]

Hello all. I am trying to size my prop. Here is what I have:

5.0Gxi-B (RPM range 4600-5000 from Volvo)
DP-S outdrive, 1.95 ratio
Currently have F6 props
WOT is 4100 RPM at 43 MPH with the F6 props
I mainly operate at about 4200 feet, and the F6 doesn't do so well out of the hole.

I think moving to an F5 prop will give me close to the range recommended by Volvo, but since I am new to this, I was hoping someone could confirm my guess. Maybe an F4 would be better suited. Since they are so cheap I want to make sure I get it right.

2002 Cobalt 206

Thank you!

 

[Maclin]

Re: Duoprop sizing

I have attached a link to the Volvo prop guide below.

Going by the 5.0gi with 1.95 ratio your mph is at the top end of an F4, meaning at 4600 that is where you would be: 43mph at 4600rpm. My guess is you are right on the cusp between an F4 and F5 regarding hitting top rpm's.

At altitude with that heavy of a boat and that few rpms a 2 step down in pitch may be called for, especially if you are trying to pull up skiers and/or always have a full load.



http://www.volvo.com/NR/rdonlyres/2D2F5550-D247-4F3D-BE18-B8D3E71BEAA6/0/prop_guide_2005_2006.pdf

 

[gluttonforpunishment]

Re: Duoprop sizing

Thank you for the insight, I appreciate it!