Hardin,
This is definitely solvable; you have the right idea. Unfortunately, this is one of those projects that is going to require some inventive testing/diagnostics or you will be stuck repeating the cycle of doing a bunch of fiberglass (and finish) work before splashing repeatedly. It will continue to seep at a non-zero rate and will slowly worsen until you get all of the microchannels patched shut. If you don’t find the ‘ends’ of all of the cracks, the seeping will continue, and slowly worsen, until it quickly worsens.
These boats are made of a fiber reinforced polyester matrix, which doesn’t have the tensile strength of modern materials - epoxies, etc - we are used to today. The hull layup was definitely not designed to accommodate a major deformation. A hard run aground that flexes the hull enough will cause internal ply delaminations that extend outward from the visible crack, internally along the ply boundaries. The water is finding these areas of internal delamination to flow along. Based on the leaks you describe, the flex was bad enough that these cracks made it all the way through the laminate.
Here are some images I found on google that should help visualize what is going on inside the layup in the affected area:
Basic point loaded delamination:
Buckling/compressive delamination:
Simplified example of internal delamination around a hole. Local surface geometry will affect the shape that the delamination takes:
You will need to make a judgement call based on the info you have. How extensively you ‘address the issue’ given what you know about the incident should be informed by two main factors: how bad you think the grounding was, and what you plan to do with the boat. In order to frame the question properly, it may be helpful to think of these internal de-laminations as “future crack propagation points” because that’s what they are. You say you heard it was bad. If you plan to go offshore, what is the peace-of-mind worth to you?
This may sound dramatic but to solve it properly, you will need to “scarf” the laminate until you have found the extent of the damage. In your case, the scarf will need to extend basically all the way through to the internal leak location:
Conventionally, you scarf back 1/2” to 1” per ply....it adds up. If you can reach from the inside, a double scarf will help reduce the affected surface area on the outside of the hull:
Finally, you lay a few continuous pieces of new glass up the slope of the scarf on all sides and fill the void with successive glass layups until fair:
If this is biting off more than you can chew, consider doing some leak testing on the hard so you can better judge the extent of the damage. The obvious thing would be to leak test from inside. You could plug up the drain under the mast step and fill the forward area with a hose. As the leak reverses, that will tell you where the leak is getting
in from outside.
Leak testing from
outside would also be informative, but it will be fussier. You’ll need to tape a big bag over the affected area with some heavy duty waterproof tape and fill the bag with water. For bonus points, tint the water with some food coloring to make chasing the internal leaks much easier.
This is all a question of time and patience more than money. May be worth just paying the yard’s fiberglass guy to go nuts for a weekend.