Below water fibrglass repair

Not sure this is the right place to put this question.

I was given a fiberglass 1983 StarCraft. In the process of removing the rotted deck I made the major blunder of getting the saw a 1/2" too far over and cut an 18" gash through the hull

How do I go about repairing this cut through the hull to make it water proof again? I was pretty comfortable with redoing the fiberglass tabbing and other work inside the boat but this one has me nervous. Once the floor is put back in this will not be accessible from the inside without cutting out a section of floor to regain access so I really need to get it right the first time.

 

Is it on the side of the boat ?

 

It is on the bottom near the rear, in the one the cut is not visible but the arrow shows where it is so you can get a better idea. The cut was made with a circular saw so it has smooth edges as opposed to something hitting the boat and causing a ragged hole

 

What thickness do you think you cut through ? Is the area adjacent to the cut, on the inside, flat, or is there a hollow where the strake is ?

 

I haven't been able to get a good picture from the inside. The cut is on a flat section just after the hull comes up. Right next to it is where the plywood floor stops then the hull shoots up about 3/4 of an inch then levels off until it reaches the wall. The cut is very close to where the fiberglass goes from being vertical to horizontal so it is right against a curve that forms that change in direction and on the horizontal piece. I would guess the fiberglass is about 1/8 of an inch at that point but I will try to get a more accurate measurement when I get home from work tonight.

 

I wouldn't try repairing it from outside, except the finishing touches, you will need to fill that gap temporarily with something you can remove later, that stops resin leaking through and running all over the bottom leaving a mess. If repairing with polyester resin, the surface prep will need to be thorough to ensure satisfactory bonding. I would just use mat, starting with bigger rectangular pieces, that extend well away from the damaged area, and then progressively narrower ones as you build the layers, all centred on the cut. That way the maximum thickness of the repair will be over the cut. Also, you get a big surface area of contact for better adhesion. I'd go with a good multi-layer lay-up tending toward over-kill. Then remove whatever you plugged the cut up with, and bog that from the outside with a suitable filler, preferably epoxy based, that won't slump out of the gap before it goes off. You will go nuts if you try and glass from both sides, inside and out, imo. But obviously you need to go about it properly, because there is the potential to start taking water dangerously if you don't.

 

This isn't all that unusual a thing to happen or to repair. Grind down 2/3's of the laminate thickness on the inside of the hull, feathering it back a few inches away from the gash. You'll replace the material you've just ground away. The grinding back thing permits a large enough "purchase" area for the new goo and fabric to bond to. Next pick you resin system and there's three choices, polyester, vinylester and epoxy. Epoxy is the easiest for the novice to use and the strongest, but the repair can be done with the other resins too. Basically, you'll bulk up the removed laminate, with new fabric, until it's at least as thick as it once was. With this performed, now you'll have a gash visible on the outside, probably with some dried goo oozing through in spots. Grind this area down, so there's a slight depression along the length of the cut. Lastly, you'll fill this depression with a fairing compound of some sort, either home made or premixed (like Quick Fair from System Three).

If you can't get at it from the inside, do the same thing from the outside, as described above, you'll just have more finish work to do. Paint over the area with a good quality paint, or you can have a shot at gelcoat, though it takes years of experience to make a good match with gelcoat.

 

Thanks Mr Efficiency and PAR. You make it sound easy enough.

I have read that surfaces exposed to the water require Epoxy but that Epoxy doesn't work as well with CSM as polyester does. Is that accurate or does it not really matter which resin system is used on this type of repair?

As for matching the paint or gelcoat I am not that concerned with appearance since this would be hidden when the boat is in the water and I am not trying to make this so it can be sold, I just want to make sure it is water worthy so my wife and I can enjoy it

The inside part of the repair will be under the flooring so it also would be hidden.

One of the videos I have watched for fiberglass repairs suggests repairing holes with 1 layer of CSM, then a layer of 1708 Biaxial, then finish with layers of CSM as needed. The 1708 adding a lot of the strength. Do you agree that is the pattern to follow to get a lot of strength or something else. I figure this area will get a fair amount of stress when the boat is moving fast enough to start to plane on the water. I would rather overkill on the strength then go weak.

 

CSM is a bulking material and not necessary with epoxy, but there's nothing incompatible about it. Any of the resin systems will do and the laminate could change to suit the resin or it could all be the same.

I'd do an all 1708 repair, with a final CSM covering on top, to offer something to smooth up. Simply, apply as many layers of 1708 as you need, until the laminate is at least as thick as it was before. You can't error if it's too thick, but sure can if it's too thin, so error on the too much side.

 

Thanks,

So my basic plan will be to do the interior part of the repair. At the same time I will make and tab in the stringers and transom. I plan to put the cap back on to help hold the shape better than the boards I am currently using.Once all that is done but probably before laying the floor to keep the weight down so my wife and I can handle the boat easier, lift off the cap again and we will take it in the yard and flip it. Then we can do the outside part of the repair easier since I would not have to work against gravity. Take the boat back inside and install the floor with the cap on. A nuisance putting the cap on and off but I wasn't happy with the cradle I made so I want to make it easier to ensure I don't have issues putting it back together.