BEYOND FLAPS THE INTERCEPTOR

Interceptor or, less commonly intruder: we’re talking about that device which is as small as it is efficient which allows to correct dynamic set up of a planing boat (while cruising) to improve performance. Even if it has become widely used many users don’t know exactly how it works and when/how it is to be used. This is how it happens, more or less: a guru of the sector or perhaps a couple of ‘experts’ may suggest it as a way of putting right a planing hull which underperforms.

Let’s try to throw some light on the topic basing ourselves on scientific study and experiments that over the past few years, have allowed to further one’s understanding of the various aspects involved. The interceptor is made up of a small protruding blade vertical blade (20-30 mm max.) which comes out of the stern end of a planing or semi planing hull in correspondence of the transom. The blade in question can retract and descend accordingly or is fixed at a given length. This way when it’s not fixed but accordingly adjustable it works much like flaps do. They’re normally deployed to stabilize and/or correct the vessel’s set up according to sea state and other factors. Furthermore, the interceptor can have a more limited surface area or can extend to take up the whole of the transom’s length.

How it works

The interceptor’s positioning can cause the bow to dip more or less according to boat speed. Changing the set