There’s no replacement for displacement. Most boats don’t come setup great for surfing as they are initially designed for wakeboarding and skiing. The reality is you need to add weight and a fair amount of it to get surfing. DELTA does its job by shaping the wake, but you still need ballast to give the wake enough energy or “push” to surf on comfortably.
For a 21-23 foot boat, we usually see people running with around 700 lbs in each rear corner and 850-1000 lbs in the center/front of the boat. Also, people count as ballast too! Although these are very generic numbers, we generally say we want to achieve a 60/40 split of weight in the boat (60% in the back 40% in the middle/front).
It is essential to understand that it is also very possible to add too much weight when this happens; all you will achieve is a ton of turbulent whitewash.
For more information on how to set up a ballast system for surfing, here is an excellent article from our website about How to Weight Your Boat for Wakesurfing.