Angle Thru hull transducer on 2001 21se?

[grasshoppper1]

hey guys,
Im looking to install a airmar 175hw & L on my 2001 21 se. But im not entirely sure what angle I’m supposed to get. Anyone have any idea that’s done it before?

 

[Postal719]

What's the dead rise? They make a 0, 12 and 20. 20 for deep v boats like mine. Installed in the rear hatch where there is clean water.