A forward slide builds directly on 50-50s in all stances - same approach, different position on the box. Instead of riding straight along it, you pop onto the box with the board turned 90 degrees so it sits across the feature, and you slide with your chest facing the end of the box. You can see the whole way out, which makes it the friendlier of the two sideways slides. The blind version, where you face back the way you came, is the backward slide.
At the park this position has two trick names depending on the edge you approach on: from heelside it's a backboard (HS FS90), from toeside it's a front lip (TS FS90). Same rotation, same slide, different edge.
The rotation has to happen in the air above the ramp, not on the box itself. If you land with the board already sideways and a flat base, the slide takes care of itself. If you land straight and try to whip the board around once you're on the box, the edge will always catch.
Learn more in this video:
Source: Johnathan Buckhouse · How to Boardslide on a Wakeboard
Key tips
- Pop and rotate as you leave the ramp, don't rotate on the box
- Keep your weight centered once you're on the box
- Look at the end of the box to keep your balance
- Ride off the end and rotate back to normal riding
- Practice from both regular and switch approaches
- Approach angle matters. Go slightly wider than a 50-50 so the rotation has room