Similar to a motorboat, however the key difference is the girl has small breasts. The giver sticks his head over the breasts instead of between the breasts as they are too small.
1: A hovercraft, or air-cushion vehicle (ACV), is a vehicle or craft that can be supported by a cushion of air ejected downwards against a surface close below it, and can in principle travel over any relatively smooth surface, such as gently sloping land, water, or marshland, while having no substantial contact with it.
2: Something that may, or may not be full of eels.
When you HAVE to use a public bathroom and HAVE to use the stall, but the seats are too disgusting to actually sit on and there's no seat covers so you have to just pull down your pants and hover your butt over the side of the bowl and drop your load in like a hovercraft dropping shipments/torpedoes.