A person is on a small boat and going down some very strong water currents.
A person on a boat is testing their own skill through some strong currents.
Just because someone is on a boat going through strong currents doesn't mean they are testing their own skill.
exists p1 x1.(exists e1 s1 s2 s3 x2 x3 x4 x5 x6.(on(x1,x2) & subset_of(e1,x2) & a_down(s3) & Manner(e1,s3) & Theme(e1,x5) & Actor(e1,x4) & v_go(e1) & n_current(x5) & of(x5,x6) & n_water(x6) & a_strong(s2) & Theme(s2,x5) & r_very(x5) & n_thing(x4) & subset_of(x3,x2) & n_boat(x3) & a_small(s1) & Theme(s1,x3)) & n_person(x1))
exists e1 s1 s2 x1 x2 x3 x4.(Theme(e1,x3) & Actor(e1,x1) & v_test(e1) & through(x3,x4) & n_current(x4) & a_strong(s2) & Theme(s2,x4) & n_skill(x3) & a_own(s1) & Theme(s1,x3) & of(x3,x1) & n_thing(x1) & on(x1,x2) & n_boat(x2) & n_person(x1))