Old as Dirt!
Join Date: Nov 2008
Location: Tampa Bay Area
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Re: Grid system repair
The yacht’s hull is solid, hand-laid, glass reinforced with an epoxy bonded partial hull liner extending roughly two feet above the bilges that was installed while the hull remained in the mold and still “green” to ensure a chemical as well as adhesive bond. The liner is comprised of a grid system designed to reinforce and stiffen the hull, particularly adjacent to the keel; mast-base; and where chain-plate loads are transferred into the hull. The liner keeps locker bottoms isolated from wet bilges and, during manufacturing, ensured the exact positioning of bulkheads. Before installation, the liner is partially cut-away between "ribs", and the resulting edge flanges tabbed to the hull with layers of bi-axial glass. This technique retains the strength added by the liner yet allows near full access to the inner skin of the hull. Penetrations along the undersides of the "ribs" for hoses, wiring et al are akin to penetrations in the webs of structural beams and of no consequence to the function of the sections.
Having "run aground", the keel would have attempted to rotate down and away from the from the keelson at the leading edge of the keel root, forward, and up and into the hull at the trailing edge. The keel bolts--16 or so--would have prevented separation of the keel from the hull hence the yacht accordingly rotated forward and down immersing the forward sections of the hull and raising the aft sections until the energy consumed matched the energy required to bring the yacht's forward motion to a halt.
The resulting torque introduced into the hull beneath the structural grid would have actually introduced transverse compression in the top of the ribs ribs forward of the centroid of the keel--hence the edges of the "cracks" in the forward ribs would likely show an upward ridge along the length of the cracks, while the ribs aft of the centroid would have been bowed upward, placing the top faces of the ribs in tension and cracks there would merely be "lines". The the corners of the intersections of the fore'n aft stringers and transverse ribs would have been likewise compressed or tensioned showing similar characteristics.
Despite the surface cracks, so long as the ribs/stringers did not separate from the hull--and the photos reveal no evidence of that--hull integrity would not have been compromised and the cracks would merely be cosmetic so long as they are merely surface cracks. One can determine that by releasing the tension on the shrouds and fore and back stays, relieving the tension on the yacht's hull and probing the cracks with a very thin probe. (Knowing the construct of the yachts, however, I doubt one will be able to insert a probe deeper than the depth of the gel-coat covering the ribs.) So long as the actual glass fibers in the section have not ruptured you have no issue other than cosmetic--which I suspect is the case. Merely clean up the glass, remove a very small area around the cracks--and I do mean small, no more than the thickness of the gel coat as you do not want to cut through the glass fibers, and full the cracks with Marinetex. If any of the glass fibers have ruptured, you'll want to remove the surface of the ribs to only the depth of the rupture along the tops and sides of the ribs and "splint" them by building up layers of biaxiel glass length-wise across the line of the cracks. This repair is actually better done while the yacht's afloat than on the hard as the yacht's weight is distributed and supported over the entire water plane rather than concentrated on the keel which will cause some distortion of the shape of the hull. If you do not have skills with glass, hire someone that does. Note, however, I doubt the foregoing will be necessary.
PS: It would be wise to clean up your bilge. Grime makes it very difficult to see what may have happened to a yacht's hull during a grounding and it makes a yacht smell bad.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."