japanese ships at the time were built with wooden planks and steel nails, which rusted in seawater after some time in service. the ships were built in a curved pentagonal shape with light wood for maximum speeds for their boarding tactics, but it undermined their capability to quickly change direction. also, they were somewhat susceptible to capsizing in choppy seas and seastorms. the hulls of japanese ships were not strong enough to support the weight and recoil of cannons. rarely did japanese ships have cannons, and those that did usually hung them from overhead beams with ropes and cloth. instead, the japanese relied heavily on their muskets and blades.