The purpose of the plastic bubble is to simply provide enough weight to cast the fly. Many of the bubbles have a removable center pin that allows you to add water to the bubble. This provides a weight that will usually float and carry the fly a good distance.
Fly fishing with a bubble is most often done in lakes and ponds from the bank. If a boat is available, the technique will allow even more water to be covered effectively.
Fly fishing with a bubble is a technique that is normally done with a spinning rod and reel. Either open face or closed face reels may be used depending on your preference. Light weight rods and reels used with light lines in the four to six pound test range are preferred to the heavier tackle used for other types of fish.
Select one of the bubbles in a small size to begin. I like to use the smallest size available as this will cause less disturbance in the water. Larger sizes will allow much further casting distances. The center pin in the bubble is tapered and has a hole. Slide the line through this hole with the large end of the pin first. The bubble should be free to slide on the line. Tie a small snap swivel on the end of the line. This is merely to keep the bubble away from the fly by providing a stop.
Next attach a five to six foot section of light leader. Fly fishing tippet material works very well here with something in the three pound range the best choice. This is small enough in diameter to be effective in presenting the fly.
Finally, select the fly of your choice and tie it to the end of the leader. Small flies seem to work the best but the selection process is the same for the bubble fly fisherman as the fly rod fisherman. Make your cast to the water you want to fish. After the bubble splashes down, wait a few seconds before starting your retrieve to let the ripples caused by the bubble to subside.
Slowly reel the bubble toward you, trying to go slow enough so that you don't cause a wake behind the bubble.
The strike is usually hard enough that you don't have to worry about setting the hook. If the fish are just "bumping" the fly but not getting hooked, the fly selection is not quite right. You are close but often times a change to a slightly different pattern will make all the difference. Fly fishing with a spinning rod and a bubble is a trout fishing technique that will open the world of fly fishing to many who don't want to deal with all the complexities of the fly fishing experience.