This topic comes up from time to time so I thought I'd jot down a few notes we can refer to whenever it might be needed. The topic, of course, is water tracks that don't slow down the trucks. A few examples include:
This is by no means a complete list; there are many many more (as well as boats to go with them).
There are three basic methods to choose from.
1. You can use Water Textures for your road and set the texture properties to water with an appropriate grip depth. If you animate the textures it can look acceptable.
The good. This method is the least restrictive. Your road can travel over any altitude changes you want to give it. And, you can use the water textures in the startup.pod (RIPPL100.RAW to RIPPL800.RAW). You can also create your own (Salmon Run by mike204) or use the mtm1 water textures (Motor Boat Madness by 2Xtreme).
The bad. Using a water texture gives the road a sharp-edged, artificial look. You might be able to compensate for this by using something like winterkill's templates, but if you animate the water you may find you have problems aligning the textures so they appear seamless. A second drawback is that the trucks lose a bit of tire grip.
2. You can insert Ground Boxes above or below the road area, and the water will take on the properties of the ground box textures. That is, the water will inherit the texture properties of the ground boxes. For example, when a ground box texture is set to concrete and you drive through water underneath the ground box, the water will act like concrete rather than the usual water resistence. To see this above and below idea in action, download this Water Test Track (57k).
The good. This method uses the game's real water. There is no attempt at artificial simulation of water because it's the real thing. The depth of the water is controled first by the water level itself, then by the terrain (lower means deeper water, higher means shallower).
The bad. Straying away from the ground boxes causes the water to behave normally. So, you must make sure you cover every area in which you want the trucks to travel fast. Also, ground boxes above the water can look ugly. You can compensate for this by placing them beneath the road. However, when you travel under a ground box, you see the trailing water effects but when the ground box is below you no longer see this. Lastly, although the game permits thousands of ground boxes, the more you use the more lag you can get in the track (as well as glow-in-the-dark backdrops and have 'mark increase box count' errors).
3. You can lower the Altitude to Zero feet for the road sections of the waterway path. Use the plane button set to 0, then make your road. It is probably a good idea to lower the entire terrain to ten or twenty feet before you begin. Then set the water level to two or three feet.
The good. No trickery. And no fear of wandering away from a narrow ground box trail.
The bad. The road is dead flat. If you add a jump in the terrain, the water resistence kicks in right away so jumps are best made using models or ramps.
Note. OLD NickAtNite made a bunch of motor boat madness tracks and boats using this method.