We study two similar spin ladder systems with the ferromagnetic leg coupling. The first model includes two sorts of spins s=1/2 and 1, and the second model comprises only s=1/2 legs coupled by a "triangular" rung exchange. We show that the antiferromagnetic (AF) rung coupling destroys the long-range order and eventually makes the systems equivalent to the AF s=1/2 Heisenberg chain. We study the crossover from the weak- to strong-coupling regime by different methods, particularly by comparing the results of the spin-wave theory and the bosonization approach. We argue that the crossover regime is characterized by the gapless spectrum and nonuniversal critical exponents are different from those in XXZ model.