Cracking Due To Shoddy Construction (images #5 & 6)
What: Separation of parts; cracks through hull shell
Where: Stringer/bulkhead/transom attachment
Why: Poor workmanship or quality control
Fix: Reapply tabbing and/or add ’glass to hull bottom
The image above (image #5) is a photograph of a boat’s bottom. The gray field is the bottom paint and the white area in the center is a chipped out section of the fiberglass hull. The chip blew out of the laminate because the stringers inside the boat were not robustly laminated and broke loose from the hull as the boat moved through the water.
Know that about 40 percent aft of the bow is typically the location of some of the higher-slamming forces acting on a powerboat hull. The following image (image #6) shows damage to a vessel that would be classified as very near to a catastrophic failure of the hull shell. It took nearly 20 years for this problem to develop to a dangerous point. The exterior of the hull shell showed only a very short crack through all the layers of bottom paint. There were several things going on.
The stiffener, the square-sectioned part on the left in the image, should have been laminated to the plywood frame it intersects but was not. Instead, the two were simply butted together. This caused more movement than should have existed had proper lamination techniques been used. In addition, some laminate was missing from the original design, making the shell even more flexible in this location. Whether this was due to cost-cutting or the lamination crew’s failure to do the job as specified cannot be determined. Finally, the quality of the laminate was poor, with both dry fiber and trapped air present, as seen through the core sample taken through the crack. Be sure to look for wide tabbing or fabric overlapping mating surfaces when inspecting a boat. Also, you can’t be expected to take core samples like I do, but do look for dry spots by keeping an eye out for white areas, indicating cloth not wet with enough resin.