Early Gravity Boost

General Information

This is probably the biggest sequence break in all of Torvus Bog. Normally, you have to go in a long circle around Hydrodynamo Station to scan the 3 scan posts and access Gravity Boost. It also involves several trips to the Dark World.
Instead, you can save several minutes by skipping this entire circle and going straight to Gravity Boost.
Conveniently, Early Gravity Boost also allows you to access the Power Bomb Guardian early.

This is the fastest possible method. However, it only works if you have Screw Attack already. If you don't, then your only other option is to do Underwater Dashes as discussed below.
To do Air Underwater, you must morph on the frame the camera enters the water, making it a somewhat difficult one-frame trick. There is no specific setup, you simply need to do it based on feel. However, it helps to be holding the L button. This way, you can use the crosshair to see roughly when you are about to enter the water.
After getting Air Underwater, just drop down and Screw Attack to the two higher scan posts. Then, drop down again to access the lower scan post and you're ready to get Gravity Boost.
This method is only fastest if you get Air Underwater somewhat quickly. If you really dislike Air Underwater, use the method below.

Line up on the top railing so that you have a straight path to one of the higher scan posts. Do an Underwater Dash while doing your Space Jump late enough not to bonk your head against the railing, but not so late that you can't Space Jump.
Use the Morph Ball cannon to go back up, and repeat this dash for the other one of the two higher scan posts.
Finally, you can now just drop down to the lower scan post and you are ready to collect Gravity Boost.
This method is slower and probably more difficult, since the timing of the Space Jump is very tricky. It's recommended to just do Air Underwater if you have Screw Attack.