Hi Rocco,

The distance from the transom (back of the boat) to the prop should be about 8% of the hull length.
In the pictures it looks too close to me.

The reason for this is that, once on the plane, there's a "dent" in the water behind the boat, if you position the prop in this dent, the prop will lose it's grip on the water and the boat will slow down.

For a 600 motor, a 39mm prop is too big, it will fry your motor.
On our seven cell monohulls with a 600 motor, we run a 36 or 37,5K prop.

What you need to do, is sharpen the transom, the rounded edges create a lot of drag you can do without...

Did you have a look at the German forum, I gave you the link to?
If you did, you'll know that a 600 motor is not going to be enough to make this hull fast...

The boat will steer better, if the rudder if positioned offset to the right, it will stand in the undisturbed flow.
Behind the prop you'll need a longer rudderblade (=more drag) to get the same rudder response.

Let me know if you need pictures or measurements.

Regards, Jan.