Blade Rake represents the angle of attachment of the blade to the hub of the propeller. This is not to be confused with the pitch, which is a measure of the twist or screw progression. Higher rake normally improves performance in ventilating or cavitating situation (high engine elevations and high trim angles).
Additionally, higher rake can provide higher bow lift, which will frequently improve speed. Low rake blades are typically used on motors with propellers running fully submerged, typically carrying moderate to heavy loads. The rake angle can either be straight or average angle of a parabolic curve.