Hi guys, I just joined the forum because I'm also trying to figure out the chine runner concept. I realise it's an old thread, but while the mystery persists, so should the thread...
Matt Layden explained the chine runner concept to the Small Craft Adviser magazine, you can read the interview here: http://www.freewebs....uild/#398015069. He emphasizes that the chine runners are only a small part - they're just a little fence between the two sides of the hull, so that when heeled, the hull is just one giant hydrofoil creating lift to windward. In addition the large rudder is responsible for at least half the resistance to leeway.
Just in case anyone's wondering what we're talking about, here's his 9' boat Elusion that won class 4 solo in the Everglades Challenge 2010:
Perhaps another reason the beam is narrow is precisely so that the boat does heel more. This exposes more of the boat's lee side underwater, sitting the chine deeper down to get the full lifting effect that's so crucial to this design. I'm guessing it's important that the boat heels even in lighter winds.
As mentioned by others, a bonus is that the high height to beam ratio makes it 180 degrees self-righting (hatches closed!) Yes it heels more, but clearly some sailors have accepted compromising their comfort in pursuit of safety, shallow draft and simplicity.
I reckon the rocker is not only pronounced to sit the chine deeper, but also to give lift - just like the top side of an aeroplane's wing. However what I wonder is, why isn't the side of the boat flat just like the bottom of an aeroplane's wing? Of course without curving in the sides, you end up with a scow, or a square punt if taken to the extreme.
For the sake of argument, lets ignore for a moment the fact that a square punt-shape might slap waves and sit higher in the water. My question is, wouldn't square, flat sides, in combination with plenty of rocker on the bottom and enough weight, give even more lift to windward?