A hovercraft is unlike any other vehicle! Because it hovers on a cushion of air there is no friction to keep it in stuck in one place.
The first thing most people notice when driving a hovercraft is that it will drift down any sloping surface (there's no friction to keep it in position). The other major problem is that the steering control surfaces are at the rear - when you turn the control to the right the back end of the craft turns left - you are not steering the nose as you do in a car. A hovercraft can travel sideways (and sometimes backwards!) as fast as forwards. The other major consideration is wind - it can and will push a hovercraft significantly off course.
The best analogy is trying to drive a car on a sheet of wet ice on a windy day. The brakes don't work and the steering has little effect!
OK.. so how do you control a hovercraft?
There is one major thing to remember - you cannot turn the craft without using thrust! If the engine is idling and you turn the rudders left they will have little or no effect on the hovercraft direction. If you turn the rudder, then apply some power, the back end of the craft will turn sideways. Unfortunately, you will still be moving in the same direction as you were before but the craft body will have turned sideways! You haven't actually changed direction - all you've done is rotated the hovercraft body! The next step in making a turn is to straighten the rudder a bit and apply a bit more thrust - this will push the craft in the direction the nose is pointing and away from the line of travel. Making a 180degree turn usually involves multiple application of thrust and rudder to get round. It's similar to a power slide in a car. One other turning technique used on small hovercraft is to lean your body into the turn - this lifts the skirt on the outside and drags the skirt on the inside which helps the craft turn quicker.
One trick with a hovercraft is to rotate the body a full 360 degrees while continuing to travel forwards - no other vehicle can do this!
How do you stop?
Hovercraft have no brakes! There are only two ways of stopping - neither of them are particularly effective in an emergency!
You can simply reduce power until the craft no longer hovers - first the skirt will drag then the hull will start dragging on the surface. This manoeuvre isn't a good thing to do on rough land surfaces - you risk severe damage to the skirt or hull if you are travelling at any speed.. The second method is to turn the body 180 degrees and apply full thrust - you will be using the thrust power of the craft as a brake.
The best way to drive a hovercraft is to continually look out for potential problems in front of you (both obstructions and changes in terrain) and be ready to avoiding action long before you absolutely have to.
Some hovercraft use skirt drag as a simple braking system control. The Sevtec designs have a control that deliberately deflates the front cushion compartment and causes the nose to drop. The UH18 can also safely drag the front skirt to slow the craft by using it's trim wing to force the nose down. Dragging the front skirt like this on most segmented or finger skirt craft will almost inevitably lead to a plough-in where the skirt will drag the hull down onto the surface - a dangerous manoeuvre on this type of craft!.
One other very important point is that you must avoid, at all costs, reducing lift power when the hovercraft hull is travelling sideways. If the skirt or hull catch on the surface during this time, the craft may overturn. Before reducing lift to stop you should make sure the hovercraft is facing the direction of travel!
You can probably now understand why hovercraft racing is an exciting and challenging sport! Travelling up a narrow twisty river is also quite a challenge!
Driving on water
There aa couple of extra things you need to be aware of when operating on water. First the hump! When a hovercraft stops on water (even if it is still hovering) it displaces it's own weight in water underneath the hull (just like a boat). When it starts to move forward, this 'hole' in the water moves with it and a small wave forms at the front of the hole. The craft needs to accelerate fast enough to climb out of this hole and over the wave - again, same as a planing boat. Once over the bow wave, the craft rides on top of the water. The speed needed to 'get over hump' depends on craft length and weight and is usually around 8-12mph. The other thing to be aware of is 'plough-in'. This can happen on most craft and, with some, can be very severe. Basically, the bow skirt starts to drag on the water surface and can pull the front of the hull down - the result can be a very sudden stop. With some craft the effect is similar to gentle braking on a car, with others the front of the hull can partially submerge and the driver and passengers can be ejected from the craft!