I think this is pretty much best advise here. I don't charge hour rates at all either. I charge per event (prices are unfortunately way lower then you have in USA). Hour rates might sound better to someone, but take a look from other side. Usually skiing race, which I cover in this time of year, lasts 2x45mins max, with 1 or 1.5 hour break in between. So basically I'm usually working (with camera in my hand) for about 1 hour, maybe 1.5h. So I can charge for 1 hour only. Problem is that with all things included into this (driving there, getting my stuff to press center, being on track way before start, waiting between first and second run, sending photos etc.) usually I go around 6 or 7am and come back (in best case) around 4 or 5pm. So I'm out and not being able to do anything else for almost all day, and for this I really can't charge 1 hour, and clients usually don't care if I need to be on track 2 hours before start, so of course they wouldn't want me to charge 5 hours. So per event (or as Jim said per day) rate is best option. At least for me.