Join Date: May 2002
Location: East Coast
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Totally agree with Jeff...From a prior post:
The cause of the problem was well established in the 1987 University of Rhode Island study by Thomas Rocket and Vincent Rose, The Causes of Boat Hull Blisters. In simple terms, what happens is this. Water penetrates the gelkote both as water vapor and as liquid water. Water is particularly good at this due to the small size of the H2O molecule. The gelcoat is a rather poor barrier against water penetration when constantly immersed. The glass fibers assist by acting as capillary tunnels to transport the water molecules into the laminate. Once adjacent to the resin in the gelkote and laminate, the water goes into chemical solution with what are known as "water soluble materials (WSMs)" in the resin in the gelkote and laminate. These WSMs include phthalic acids, glycol, cobolts, mekp and styrene which have not gone to full cure in the hardening process. To varying degrees they are present in all cured polyester resins. Five percent is an excepted norm. In some rare cases the quality of the materials or their application may be inferior causing a higher than normal percentage of water soluble elements."
This from Steve D'Antonio:
So why are blisters and hydrolysis a problem? Well, the blisters themselves slow the boat and are unsightly. The blisters slowly delaminate the fiberglass laminate locally and if there are sufficient number of blisters, may direct affect the structural integrity of the laminates. Nothing seems to scare off a potential buyer faster than blisters though this is changing as the buying public becomes more familiar with the problem and the effectiveness of well done repairs. The affects of hydrolysis on the resin, however, are of more concern than blisters. The hydrolysis process softens, weakens and removes the resin from the laminate, thus reducing the rigidity of the laminate. As rigidity is reduced, the amount of flex experienced in portions of the bottom increases. With increased flexure comes increased risk of fatigue failure. Most yacht hulls have a safety factor of 2-4 to 1, leaving quite a bit of room for deterioration. These safety margins, however, vary widely and are constantly under pressure to be reduced in the name of performance. If a hull is of cored construction, structural damage can occur quite quickly. Large scale core saturation is largely irreparable at a reasonable cost. It should be noted that the presence of water alone in a glass laminate, even when no hydrolysis damage has been done, significantly decreases laminate's resistance to structural fatigue.
In 1991, Zahniser's commissioned Comtex Laboratories to analyze the physical properties of laminate panels removed from the bottom of Gulfstar 50. The laminate was highly hydrolyzed. The bottom was clearly deforming from water pressure due to immersion suggesting low laminate rigidity.. Test results on these panels showed a fifty percent reduction in rigidity from the new condition. Tensile strength, however, was not greatly effected. The loss of rigidity is significant as the bottom will flex ("oil can") more over bulkheads and other hard spots and eventual time to fatigue failure will be shorter. We also tested a "repaired" panel, using the methods discussed in this paper and achieved rigidity approximately 130% of the theoretical new condition.
In real life, we are starting to see failures in hull bottoms we think are directly related to hydrolysis damage to laminate resin. In six separate cases, we have seen serious, though the hull fractures at the keel roots on fin keeled sail boats. In each case, the laminate resin was severely hydrolyzed. We have seen two cases of laminate fracture across bulkhead hard spots in two powerboats which we thought were related to hydrolysis of the laminate resin. The good news is that eight boats is not a lot of boats, but consider that these are only the ones that we have seen. Surely there are more out there and surely there have been boats lost for these reasons as well. Accident investigation on sunk boats is not like aircraft crash investigation. Unless the boat is in the way, it is usually not raised and the cause of sinking investigated.
I hope this 8 boat sample from an out of the way repair yard in the southern Chesapeake is sufficient proof that blisters are more than a cosmetic problem...or that they can be fixed simply or cheaply.
No longer posting. Reach me by PM!
Last edited by camaraderie; 02-06-2009 at 03:33 PM.