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by Kurt Smithgall
March 10, 2011
Fixing a boat consists of 3 steps: Cleaning, Layup, and the Finish.
Cleaning: In order for a patch to bond to a surface, it needs to be rough with lots of fine grooves. First remove any loose chunks and fibers. If you are patching on top of shiny hull or another new patch lightly sand to make it rough (80 grit sandpaper works good). The next step is to make sure the surface is completely free of any dirt particles, oils or water. I usually give it a good washing with lacquer thinner or any other solvent like acetone, or paint thinner. Next let it dry at least 10-15 minutes before starting with epoxy.
Layup: The next step is to cut the cloth patches. Kevlar is the go to fabric for exterior repairs, but make sure you have sharp enough scissors to cut it. Carbon is sometimes used for inside repairs because it is incredibly stiff. A general rule is one to two inches bigger than the crack or damaged area. When cutting the cloth, never cut square patches. It creates a stress line and increases the likelihood of it developing stress fractures and breaking along that line. Instead cut ovals or make sure long lines are arched. The number of layers depends on the severity of the damage. 2 or 3 is usually good. The smallest patch goes down first and should be at least ˝" smaller all the way around so that is doesn't create another stress line. For resin I use west systems epoxy. The hardener depends on temperature so make sure to check the minimum temperature. The warmer it is, the faster it cures, but be careful. I used the cold hardener in the middle of the summer and the resin container melted because it reacted so fast and got really hot.
When using resin less is more. Lay out wax paper, put the patch down and dap some resin on it to slowly work the resin in. When the cloth is saturated put another layer of wax paper on top and squeegee the extra resin out. Once the cloth is saturated, you can't squeegee out too much - you're only making it lighter. You can do each layer individually or get the bottom cloth saturated then put the next layer on top and squeegee them both together, it doesn't really matter, as long as you get as much resin out as possible while making sure the cloth is completely saturated. Next the patch is placed over the damage and starting from the center press the cloth down and work out any air bubbles.
Finish: For inside repairs, I don't usually put plastic on it. I just rub a little more resin in to make is smoother. But on the outside smoothness is key. Most people use plastic wrap and then stretch it to work the wrinkles out, but it can take a really long time. What really works well for me is the enormous zip loc bags. Not quart or gallon size but the 2' by 3' ones (I think they're called XL bags). They are a thicker plastic so the don't wrinkle as easy and it takes much less effort to make it look nice. Just get one of these huge bags, cut it open, and make sure of which side the print is on, because if you have the printed side next to the resin it will get transferred onto the resin. So just cut the plastic big to allow for runs, lay it on, work out the air bubbles and slightly stretch it and tape it to keep it taunt and in place. Then check it in 15 or 20 minutes because air bubbles have a tendency to form right after you walk away. It should dry solid in 12 hours and to maximum strength in a few days. If there were air bubbles you can lightly sand it or just let the rocks take care of it. If it's absolutely awful, just get a heat gun and set it around 500 degrees, then with a putty knife you can peel it off and start from scratch again.
Front: The pads should be least 6 or 7 layers with the last 3 of fiberglass for abrasion resistance. Cover the boat with plastic wrap and tape it down. Start at the bottom and work up, so any runs stay on the plastic. How wide, and long you make it are up to you. But again because of the different layers make the each layer successively bigger with the largest on the outside. My first layer is usually 1" tapering down to ˝" then each one after gets a little bigger. My last layer is usually 4" at the front and 5" at the back. Now because of the curve of the bow you can't just lay it on and cover it. Once the layers start to get over an inch wide on the curve you need to start cutting them. This is done before you put resin on it. Make cuts over half way though about every inch or so. The idea is so that when you place it on the curve that you tuck and fold the extra under so that it lays flat. Once it's all layed up, cover with plastic wrap, stretch and tape. The big bags don't work because they don't stretch enough for the front.
I admit that the fronts are a major pain and I have accepted the fact that I will never be able to make a really nice smooth one. So good luck ...
Back: At least 8-10 layers, the last 3 fiberglass. Cover with plastic wrap… Same idea - start narrow and go wide. The first layer is roughly 2" at the back and 3" at the front and last layer is 5" at the back and 12" at the front. And for a few layers make them a little long on the back and cut and fold so you have back flap that you can drill a hole and tie a cord to. Cover with the big zip loc bags, stretch and tape.
This is not meant to be taken exactly word for word, but this is merely what has worked for me. Crunch pad sizing depends on how much protection/weight you want.
I hope this information is of some help to you.