Be very careful. I used a 1/8" drill bit. But I may have to enlargen since the large cyringe I got (2 oz capacity)to inject the epoxy has a bit larger nub of a nozzel on it than 1/8". I want to get a good tight seal so I can inject with some reasonable amount of pressure to ensure complete wetting of the delaminated area.
How deep. Well mine is a 1975 and it too sat out I think for its entire life. My oft spot area was large. Anyhow. The top skin in very thin. I'd say only like 1/16 of an inch. And the foam core is only about a 1/4". Use VERY little pressure when going through the top skin. As once you hit the foam there is no resistance and you'll go through the foam lickity split and through the bottom skin. The bottom skin is very very thin from what I could tell, like one or tow layers of fiberglass cloth. Trust me on this. I drilled straight through in several places. And now I have to come up with a fix.
If I were to do this again, I would put some sort of tape around the drill bit or may even think of buying or cutting a drill bit to make it very short. Such that only about 1/8" or so of the bit was available to cut or left sticking out from the drill chuck. Or develop some other "stopping" mechenism to prevent drill through.
As far as a fix for the holes I drilled all the way through. I'm thinking that I will get a wood dowel and coat it in epoxy resin. And stick it in the hole. I will shove it so that it continues through the hole and I will keep pushing it so that the top of the dowel is below the top skin at about the same level as the foam or possible a bit lower. I will then put a couple of drops of epoxy over the top of the dowel to seal it off. It will let it cure and then test to see that it is sealed. When this is done, I will then proceed with doing the rest of the repair as stated or shown above.
At the recommendation of my local Hobie Cat dealer from a person who does fiberglass repair for his living. He recommended to use West Systems epoxy and drill holes on a 1.5x 1.5 inch grid pattern. This is because the west systems eoxy is thiicker and does not flow as well as "Git Rot". But he also said it is a lot stronger. He believed that Git rot is only good for a couple of years before it will give up and delaminate again. The West Systems epoxy stated that you can thin down and make it more flowable but you would also decrease the strength of the resulting resin by the same amount. So if you thinned it 50% it would only have 50% of the strength. So the very think Git Rot must not have anywhere near the strength of the West Systems epoxy. I am also a pilot and am into Homebuilding airplane movement. I know that West Systems Epoxy is also used to build airplanes so I think I'' put my trust in this epoxy over the Git Rot. But that decision is a personal one and other may not agree.
If I had a smaller area of delamination say 6 to 8" diameter, I would probably have used the Git Rot. But my area is appoximately 2 to 3 FEET long and probably 5" wide. And the foam core has subsided a little in the center. So I felt I needed the strongest epoxy I could get to bridge this and secure the area. But I do have a lot of holes and it will not look good. But then again my 1975 extremely faded orange hulls don't look to good to start with. But I'm not into racing and will not go out in strong winds and only paid $350 for the boat to begin with.
This just shows you get what you pay for!
I too am intimidated. But right now with the situation I have is that the boat is worthless and useless without the repair. And if I pay a fiberglass person marina rates I would have several times more into it than it is worth. So I have little choice.
I may do the repair this weekend. But epoxy set up faster with hotter temperatures. And with my large area, I want to have decent working time to ensure that I have fully wetted area. This weekend is supposed to be lik 90 degrees. So I may wait to see if I can get cooler weather or at least time it so that I do it early in the morning when it is cooler.
I'll let you know how this goes.
