Are flatter boards faster ?

The answer is Yes, No, and Maybe. The unspohisticated rocker 101 theory says that flatter rocker is faster as flatter rocker reduces drag

There are a few ifs buts and maybes which should be kept in mind however regarding the flatter is faster idea:

1) Rocker is relative to wave curve. If the rocker is the same as the wave curve, then the rocker is effectively zero. If the rocker is LESS than the wave curve, the board will nosedive, pearl, or have its control compromised ( unless the board is rolled on to the rail in order to present the planshape curve instead of the rocker )

2) Less rocker means less lift, which can entail less acceleration on takeoff. The lift produced per square inch of wetted surface area is proprtional to speed. More rocker ( particularly in the nose ) thus gives the advantage of much greater lift at low paddle in to takeoff speeds, and this can give vastly superior acceleration during those crucial moments. Gains made at the moment of takeoff can pay big dividends later in the ride.This also applies to re entry from the lip during the ride.

3) Less rocker can reduce control with some planshapes and in very long boards.

4) More rockered designs gain speed partly through their ability ( if designed correctly ) to have such good control and ease of turning that they can have near perfect wave positioning. Thus they can fit into more curvaceous parts of the wave ( high lines for speed often entail this ). Ideal wave positioning is a great boon and often enables more rockered boards to leave the flatter boards in their wakes. Having said that, it's true that shorter flatter boards are at no positioning and control disadvantage if well designed.

5) The control and leverage advantage which more rocker can give, allows ( at least in my designs) the board to be used to present fin or fins at the most beneficial angles for lift. In short the fin(s) can be used to supplement the upwards lift provided by the surfboard hull, ( even with vertical planar fins ) thus reducing the load on the hull ( and therefore drag ) as a result. This is a somewhat esoteric subject, but the success of the concept has led to our use of very large single fins on very narrow tails. . . a combination which is a mystery to those who subscribe to the conventional wisdom that fins are only used to hold the tail in !

Regarding rocker and fins, when horizontal fins are used ( wings and tunnels for example) the effective tail rocker can be determined by the angle of the wing or fin rather thanby the bottom of the board.

6) Highly rockered boards are more easily able to reduce wetted surface area as speed increases ( lifting the nose out of the water ), thus although they can have higher drag per square inch of surface area, they are able to reduce drag by reducing surface area.

Here's an efficient rocker type with a higher nose curve and flatter tail curve which has most usually only been used on shortboards, it's a very good longboard rocker also: