Complex sentence: As their fishing boats were heavy working boats, and filled with fishing equipment, they needed a new type of boat; early boats were developed from single masted fishing cutter designs and twin masted yawls, and latterly into the specialist pilot cutter.
Split into simpler sentences: As their fishing boats were heavy working boats, and filled with fishing equipment, they needed a new type of boat. Early boats were developed from single masted fishing cutter designs and twin masted yawls, and latterly into the specialist pilot cutter.