OK then grind all the loose and cracked stuff away. The aim of the game is to remove the damaged glass without touching the underlying foam at all. If you take chunks out of it it'll be trickier to repair. Which is why I use the knife.
A vacuum pump is a bit different to a vacuum cleaner. They are more like compressors and designed to suck high-pressure vac for prolonged periods of time without breaking down. You average home or industrial vacuum cleaner won't do that. They also vacuum at a lower rate, as a rule.
With access to a vac my plan changes a bit. I tape a plastic seal around the damaged area to make it fairly air-tight. Then I bore a hole about 1/4" or so in the nose and/or tail (avoid the rail lines please). Lay the board so one side so the rail is down and attach through the vac lead plastic (make sure you use a moisture trap or you'll get water in your vac pump).
Start the vac and wait for the water to drain. The bad news is how long it'll take depends on how long the water has been seeping into the EPS beads.
Once the core is dry the actual repair work will start. First youll need to sand/grind a feathered band at least 4" wide along each side of the damaged area. Then you may need to reseal the EPS. You'll need to decide what you are going to do about the aesthetics. And then it'll be time to start laying in your replacement layers of glass and EPS while incorporating your aesthetic fixes.
The tricky bit is making sure the rocker doesn get all messed up. Because with damage like that the board is going to have a certain amount of give in the center. But that's doable too.
BTW check out the work of "the Board Lady" at
http://www.boardlady.com/. Massively inspirational! Most of her repairs are on composites but the principles still apply.