premise: One person kayaks as another kayer sinks their boat.
hypothesis: A speedboat goes by
explanation_1: In sentence 1 a kayaker sinks their boat.  In sentence two no people are mentioned.  It is only stated a speedboat not a kayak.  The speedboat goes by but we do not know what the speedboat passes in contrast to sentence 1 where the kayaker sinks the boat.
premise_logic: exists e1 x1 x2 x3 x4 x5.(n_boat(x5) & of(x5,x3) & n_thing(x3) & n_kayer(x3) & Theme(e1,x5) & Actor(e1,x1) & v_sink(e1) & as(x1,x4) & n_kayer(x4) & -(x4 = x3) & Time(x1,x2) & n_kayak(x2) & n_person(x1) & card_eq_1(x1))
hypothesis_logic: exists e1 s1 x1.(a_by(s1) & Manner(e1,s1) & Actor(e1,x1) & v_go(e1) & n_speedboat(x1))
premise_sim: exists e1 x1 x2 x3 x4 x5.(v_sink(e1) & of(x5,x3) & n_thing(x3) & n_person(x1) & n_kayer(x4) & n_kayer(x3) & n_kayak(x2) & n_boat(x5) & card_eq_1(x1) & as(x1,x4) & Time(x1,x2) & Theme(e1,x5) & Actor(e1,x1) & -(x4 = x3))
hypothesis_sim: exists e1 s1 x1.(v_go(e1) & n_speedboat(x1) & a_by(s1) & Manner(e1,s1) & Actor(e1,x1))