Now that I'm doing in the mid 50's, and am tweaking to get in the low 60's, I have another issue -when I make anything other than wide turns, the steering gets 'squirrely,' menaing it will spin out into a 90-degree or more tunr. Current pics of my setup are shown below.
note 1: as you see, the prop is about a 1/2 inch further out then the rudder.
note 2: any other rudder shorter will make sterring worse.
note 3: this has been the best prop for speed, having the prop shaft 1 1/2 inches below the keel of the boat.

yes your going in the right direction so far for speed, 3 blade will be what gets you there! What steering servo are you using? and does it do it left and right or just right? and when you say spin out you mean just go back the other way or completely around like a donut? I need more info to help you, You may need to add a turn fin if you have a good servo or make your rudder smaller and sharper like a knife. Not in length bit thickness and width, Whats the length of your hull? is it stepped on the bottom? what kind of linkage are you using to move your rudder? cable or push rod?

yes your going in the right direction so far for speed, 3 blade will be what gets you there! What steering servo are you using? and does it do it left and right or just right? and when you say spin out you mean just go back the other way or completely around like a donut? I need more info to help you, You may need to add a turn fin if you have a good servo or make your rudder smaller and sharper like a knife. Not in length bit thickness and width, Whats the length of your hull? is it stepped on the bottom? what kind of linkage are you using to move your rudder? cable or push rod?

The steering servo is a Futaba S5301; sterring is left and right;the hull is 43" long and is a stepped bottom; she 'spins out' almost 180-degrees unless I take wider turns. More pics atached (so, a tun fin may help? What style and brand, and website?) -THANKS!