In rule 42.3(c) surfing is explained in brackets = rapidly accelerating down the front of a wave. This is not nor necessary planing. I believe that Dragin can accelerate down the front of a 70 cm wave.

Assuming that these are the types of Dragons you are talking about:

then, no, these boats will not surf on a 70 cm high wave.  I would say the boat is surging and not planing or surfing as a 70cm wave will not be long enough for surfing and in 10-12 knots this type of hull will not be planing.

You have to differentiate what is happening into three types: planing, surfing, and surging.  Most people confuse surging with planing or surfing.

Planing occurs when the wind forces on the sails are suitably large enough to cause the hull to develop hydrodynamic lift that takes the boat beyond displacement mode.  This is generally independent of any wave action.

Surfing happens when a boat accelerates down the face of a wave due to gravity.  You can think of this like a skier going downhill.  The effective wave length (the wave length that the boat sees because of its angle to the wave) must be greater than 2x the length of the boat in order to surf.  The boat can then travel at the speed of the wave but no faster as it will run into the back of the wave ahead of it if it does.  If you are not going 'downhill', you are not surfing.

Surging happens when a boat is initially going slower than the wave speed.  In a wave the water molecules are primarily moving up and down, however, they also have a circulation that moves the water at the top of the wave in the same direction as the wave.  This is the force that causes the boat to surge ahead.   When the length of the wave is larger than the boat, the wave will lift the stern of the boat and push the boat forward.  As the wave passes underneath the boat, the boat will level out and then as the wave passes the boat of the boat, it will lift the bow.  Wave lengths that are shorter than the length of the boat will push the boat forward but not cause as much change in the trim.  You can almost consider this as a little 'wave current' that is moving the boat forward at the top of the wave and in the opposite direction at the bottom of the wave.

When a boat is surging, you can trim the sails to the new apparent wind angle, but pumping the sails, etc. would break RRS 42.

A “perfect answer,” but not governing. 
A boat of any length can ride a set of waves (such as a competitor’s bow waves) each of shorter “frequency” than her LWL for an extended period of time. 
In so doing she rides down the greater combination of wave tops over the lesser combined opposing wave bottoms. 
She is surfing one of those waves. You choose!

So, John writes that a Dragon with 5,7m waterline, sailing diagonally down a 70 cm high wave ( which can have from 7 to 15m length), accelerates and pulls a sail to attempt surfing, deserves a penalty (PUMP 3). I am not so sure.