Before the Captain gets into how to repair fiberglass boat stringers the Captain will try to explain what fiberglass boat stringers are, their purpose and how to detect a weak or broken fiberglass boat stringer.
Fiberglass boat stringers are longitude structural members that add strength to the fiberglass boat hull and boat transom. They run down the bottom of the boat hull from the boat transom to the forward bulkhead. On an inboard powered fiberglass boat they often support the main engines. Lower boat deck or cockpit sole are generally supported by the boat stringers. Fiberglass boat stringers are made of various coring materials such as wood and high density foam like Tuff-Stuff marine board which is made of rigid structural polyurethane fiberglass materials and is supplies catalog #TS48. Another popular choice by ARJAY PERFORMANCE PRODUCTS is ARJAY 6011 Fiberglass materials and supplies catalog #ARJ-PT. A few use solid reinforced fiberglass at varying prices.
Okay, hope you got that. Now how can you tell if a fiberglass boat stringer is broke or weak? Well you are going to have to get under the fiberglass boat hull and look around a bit and bang around on the hull bottom! Yes the Captain gets under the fiberglass boat Hull with a rubber mallet and beats the hell out of her! When you bang around on the Hull bottom you will detect different sounds. When you find the boat stringer it will be a more solid thump. Now start at the boat transom and work forward to the boat bow. While listening to the thump look for deflection and stress cracks in the fiberglass boat hull. If the Fiberglass boat hull is tight as a drum then no serious deflection is going on and no stress cracks in the gel-coat of the fiberglass boat hull are sounding. The boat stringer is not showing any signs of failure. You can inspect the fiberglass boat stringer from the inside of the fiberglass boat hull by tapping around with the handle of a screwdriver. Again listen for change in the sound. If it is a hollow sound it means repair.