OOPS! Too much grinding
 

So after months of too much work to get anything done on my project, I decided to spend the day getting the transom ready for the new core. I found several voids in the transom that were no doubt that way from the factory layup (you can kind of see them in the first pic). It looks like 2nd layer of matt (I'm guessing here) was not bonded to the outside skin/gelcoat layer. I got a little happy with the grinder getting rid of all of the voids and actually put a hole in the bottom of the boat (3rd pic). Now my dilemma. I went too deep to retain the structure of the hull in this area. I was thinking I now should modify my lamination schedule to put back the glass I ground away. I took the stringers back about 28” from the transom (2nd pic); I was thinking of going back with 1.5 oz., matt then 1 layer of roving wrapped around the corners with about a foot of tabbing. Then I would lay in 1 pc 1708, then the core then a few more pcs 1708. I made enough room to put lots of long tabbing, at least 2 feet. I feel like I am pulling a solution out of thin air and I would rather ask the question. Is this the right fix? Should I do anything different? Any help is appreciated.

1. put plastic on back side to keep fiberglass from pushing out of the hole.
2. cut three pieces of glass first with a 1 inch overlap of the sides of the damage then next piece 1" larger than last.
3. layer up wet on wet
4. good to continue with restoration

Thanks, I didn't really communicate the length of the thin spot. I have no roving left for about 3 feet at the corner of the bottom and transom. I only made one small hole but I had to dig through the roving over a long section of the bottom/transom corner to get to good glass. I just thought it would be better to replace roving all along that corner before coring the transom in - maybe overkill! The skin on the transom is thin too so some thickness there wouldn't hurt. The Coosa transom will be tied in nicely so I guess that will carry the load but the glass between the Coosa and the gelcoat is way thin and has no structural glass left; its basically matt.

I wouldn't go out and buy roven to replace the roven you grown out, I would just use the 1708 you already have. If you have the roven you can use it but the biax in the 1708 is stronger than the roven due to the nature of the flat strands. The woven strands are not pulled as tightly as they weave up and down around the 90 degree opposing strands. Plus the glass to weight ratio makes the 1708 much stronger when applied right. I would just build it back with the 1708 by laying a narrow strip in the corners and then a slightly larger one on top and then slightly larger so on and so on until you have plenty of build out and a nice radius in the corners. You don't want a hard 90, you may even want to radius with a filet then build off of that. Also where it cracked all the way threw to the outside or is open to the out side of the hull you will need to feather that back from the outside and then build it back up with some csm so that you can smooth that out. That will prevent the crack from showing up threw your paint work.

exactly. I would write more, but no need to. use 1708, build back the thickness.

Thanks for the advice guys. I was a little panicked when I saw daylight coming through the bottom and realized all the roving was gone. It sounds like the fix is not as big a deal as I thought. If 3 or 4 strips of 1708 will do it I can probably lay them in at the same time the core goes in.

One more thing. Yes to 1708. BUT.

1708 is +/- 45 degrees as it comes off the roll. So you might want a layer of 0/90 in there. Which can be a piece of 1708 cut at 45 degrees bias off the roll. That would likely be preferable to a pure +45/-45 layup.