The jib is a big factor in putting pressure on the leeward bow causing it to submarine. You could either slack the jibsheet a few clicks or be ready to uncleat it very quickly as you see the bow start to dig in. Unfortunately that isn't always that easy to do quickly on a P18 or P16 from the wire. If you're on a screaming reach have your crew leave it uncleated while they hold the sheet. I've pitchpoled a bunch of times. No one has ever gotten hurt. You'll learn what you can and can't get away with.