Complex sentence: The boats were built in Co. Kerry, and about 100 were built starting with sail number 1720, and although very successful, it was considered that the 1720 had some shortcomings, namely too powerful a rig, whcih meant that the boat required too many crew.
Split into simpler sentences: The boats were built in Co. Kerry, and about 100 were built starting with sail number 1720. Although very successful it was considered that the 1720 had some shortcomings, namely a bit too powerful and requiring too many crew.