Note, this relates to the second half of this planet.
If you got the speed achievement in part one, you still have to do this one separately.
There are a few good places to unlock this on the second half of Nautica 2
From the key/pick up at the top of the beach/hill (the one located on a black curved structure). You can use gravity on the long slope to get speed. I think I unlocked this in ball form just by rolling all the way down.
Further along the beach, between the farthest pick up and the one atop the hill, there is a gulley in the cliff, at the top is a booster, you can use this and fly out towards the sea and the power up, and if done right, gliding downwards, you can keep the speed
Finally, a bit of an exploit I found. At the top of the hill is a steep overhang with pointed rock structures. Use nearby sloped to get on top of it. There is an invisible wall trying to push you back, but if you use gravity in the right spot, you can force your way down the slope on the out-of-bounds area. Get down near the water line, then let go of gravity, the game will try to push you inbounds, imparting high speeds to your craft. If lucky you can do this without it disabling your glide and jump. Glide when you can (sometimes only once back inbounds) and you should get launched from the top of the cliff with great speed. I used this method to get my height achievement here.