a. Golden hour
Golden hour is the term photographers use when
period of time one hour after sunrise and one hour before sunset. This is when the sun is low in the sky, and your subject (rider) will be lit by warm and rich colorful sunlight. When shooting during magic hour, you (the photographer) should keep your back to the sun, and keep your subject facing the sun. You can also experiment with having the sun on one side for sidelighting. or shooting directly into the sun to silhouette your subject.
Taking photos while the sun is high in the sky will
unflattering photos. Colors will not be saturated, and the image won't have much three-dimensionality or depth.
c. Twilight and low light
Many extraordinary photos are made
is very little light in the sky, and flashes/strobes are used. In order to properly light these photos, you must be very close to the action (10ft or less...not from the boat), or have powerful and expensive monolights or powerpacks and strobe heads. If you have a housing for your camera that will accomodate a flash, you can create incredible tube shots. Some photographers use remote mounted flashes, or they shoot from one location and have an individual in another location holding the flash. Doing this requires expensive radio triggers such as PocketWizards.