The principle is simple.
Fluid flowing over a surface tends to stick to it (Google Coanda Effect). it's worse at the low Reynolds numbers that model
s work at. The result is that water displaced by the boat at speed tends to flow up the sides of the hull, sticking to them, and can even pour onto the deck. This slows the boat down and can swamp it.
If you have a sharp chine
, you can force the water to move away from the hull at the discontinuity, because it can't easily flow around a sharp angle. ideally, you can deflect it downwards and get some lift, helping the boat onto the plane. So a lot of model
s have small rails along the chine
, shaped to deflect the water downwards a bit. This is what many of the Aerokits model
Deep Vee design relies on these a lot - the bottom of the hull has a series of parallel spray rails
so that as the boat rises in the water the spray
is deflected downwards by each rail in turn and an ever-smaller part of the hull bottom is wetted - reducing drag a lot. But the Sea Queen is not a Deep Vee, and doesn't need more that the one set of rails along the chine
Deep Vee spray rails
can also help to cushion the shock when a boat drops back into the water after leaving it - but that's more useful in full-size practice rather than model