  We consider the 3D hyperviscous Navier-Stokes equations in vorticity form,
where the dissipative term $-\Delta \vec \xi$ of the Navier-Stokes equations is
substituted by $(-\Delta)^{1+c} \vec \xi $. We investigate how big the
correction term $c$ has to be in order to prove, by means of Girsanov
transform, that the vorticity equations are equivalent (in law) to easier
reference equations obtained by neglecting the stretching term. This holds as
soon as $c>\frac 12$, improving previous results obtained with $c>\frac 32$ in
a different setting in [5,14].
