by Roger » Sun Jul 23, 2006 11:52 pm
You must bridge that gap, not just fill it. From the outside, I would take off a the layer of gelcoat completely up to 2 inches on all sides and ends of the crack, right down to the cloth. Could use a dremmel for this, but a belt sander will get you there very quickly. Be very careful and apply the sander is short 1 to 2 second spurts, then check your work. Do not use an angle grinder, it will take it off too quickly, A belt sender is almost too fast as well, but a palm sander will take hours! You will now have a crater four inches across, by however long the crack is, plus another 2" on each end. Now with the dremmel and a small drum sander, take out the first layer of cloth about an inch on each side and ends of the crack.
If possible do this repair with the boat careened onto its side, or even better upside down so that gravity works for you. That may not be practical but working this kind of repair from under the boat is really challenging. Widen the crack to about an 1/8 of an inch, clean with acetone and let dry.
Using polyester resin (not epoxy) fill the crack and saturate the bottom of the crater that is 1 inch wide on either side of the crack, add a saturated fg cloth strip the same size (2 inches wide, or slightly wider 2 1/2" then before it cures, saturate the whole area, and add a 4" wide strip on top the same size as the crater. Let this cure, then the next day clean off the amine blush with acetone and cover the whole area with gelcoat, or if you are planning on painting the repair, just with polyester resin until the repair is at least level with the surrounding area. After four days, (cured and final hardening) use a Palm sander with 80 grit, knock down the high spots and get an initial flat finish, move up to 120 grit, then 320 or so, and finally finish off with 400 or 600 to match the finish of the surrounding area. If you are painting wait four days.
This now gives you a base to start working on the inside if you can access the crack from there.
You want to beef up this area as much as possible, so yes you will have a hump, but it will be on the inside, where it will not affect bottom performance.
On the inside, clean out the crack with your dremmel tool to about a 1/8" V shaped groove. You will not be creating a crater like you did with the outside. Give the surrounding four or five, even six inches a good sanding with 80 grit, but basically just to get a 'tooth' on the surface. You want to keep as much existing fiberglass here as possible. Clean with acetone, let dry and again fill the crack with polester resin, paint the area with resin, place a fiberglass cloth saturated with resin over the area but short of the edges of the sanded area by about an inch and a half. While this is still wet cover with a second layer of cloth, this one extending to about a 1/4 inch from the edge of the sanded area.
Do all of this work on cooling temperatures, ie after the heat of the day. If you do it as temps are increasing, tiny bubbles will appear in your work from heat expansion. If you do it on cooling temps, the resin will actually soak into the toothed area better, and you will get a better mechanical as well as chemical bond.
If the crack goes right up to the centerboard case you may also want to strap the lower end of the cb trunk just above the crack to reinforce it. Do it the same as the first repair, but just add 2" straps of saturated fg cloth on to the similarily sanded and cleaned area. Make sure your straps wrap around the front of the trunk and extend back at least 6 inches on either side.
It will definately look reinforced on the inside, but at least you should not get any leaks.
This is likely a minimal fix. If you were wanting a stronger fix you may extend your repair up to 9" on either side of the crack.
One further item, to make sure to check. Although you think the visible crack is only two inches long, assume the hairline crack goes another inch at least. Groove it out while your are doing the visible crack and repair the whole area as one.
Finally when using fg cloth, do not use the woven stuff, get chopped strand matt. It saturates better, and is more water proof than the woven cloth.
If you have never worked with fiberglass, do a little bit of reading first to familiarize yourself witht he process, but after you've done it once, you will not hesitate to do it again. Use a mask, protective clothing and latex gloves. Use disposable containers, mixing sticks, foam brushes, etc. Resin kicks best at about 60F degrees, so for a few days before you do your repair, watch your daily temps and id the time they peak. This is when you want to start your repair. Also if you are working outside, work in the shade, the direct sun makes it kick faster and may create bubble. One trick with moveable work is to let in sit in sun, under a green garbage bag, then move it to the shade to do the work.
Hope that helps.