Rub Rail Fiberglass Repair along Gunnel Cap

[Miflinite]

The boat is still sound where the gunnel cap and hull meet, but there appears to have been some rub rail damage in the past. What would the best course of action to fix fiberglass in the pictures? Would a filler only be good enough since it is hidden behind the rub rail, or does the filler need to be sealed with a sheet of fiberglass?
Thanks in advance for any advice.

 

[Meanwhile]

Wow.
I'd make some structural filler, or buy some, then apply to cleaned surface. But I'm just an arm chair observer on that. Lots of leak potential.

 

[Hookup1]

I just got done with a much more serious repair on my boat. I had a crack under the rub rail. I took the whole corner off, replaced the filler with marine plywood, reinforced epoxy and re-installed the glass.



This looks like a boat that was rubbing up against the dock or pilings for a while. The rub rail screws into the fiberglass top and bottom half of the boat.There is not a lot of reinforcement behind the edge the rub rail sits on. The rubbing works the screws in the rub rail until they are loose and then work like a saw on the screw holes. I would try to get some material (reinforced epoxy or glass cloth) behind the screw holes.

I would get some West system 105 epoxy, 404 or 406 filler and 206 slow hardened. Thicken the epoxy and use a caulk gun shell (West System) to squirt into the voids and fill the rail. Maybe add a layer of glass cloth over the vertical edges to add support and reinforce the screw holes. Clean off and smooth before it hardens. These fillers are hard to sand.Then re-drill as you install rub rail.

Another option is to work with glass cloth in small epoxy batches, wet the cloth and push into the holes. Then go over with reinforced epoxy. The glass cloth will give the screws something to hold on to.

 

[seasick]

The damage is severe but as long as the 'flap' between the two open cracks is sturdy and doesn't flex, a cheap fix can be done. Just make sure the cap is tight to the hull and doesn't move when lifted or pressed.
Since the major damage is under the rub rail, you can patch with MarineTex or a structural filler as mentioned but the MarineTex will work and is fairly thick so it is less likely to sag.Yoy may need to put some sort of backer in the holes and that can be as simple as a small piece of fiberglass cloth with a thread inserted in the middle to give a way to hold the cloth 'tight'. You can apply some resin to the cloth first to help it stick (on the backside of the crack). Let it set for 30 minutes or so or until firm but not fully cured and then snip off the thread and partially fill with MarineTex (or polyester resin with a filler). When all the cracks are done you should caulk the seam with something like Sikaflex or LifeSeal. I would also fill the screw holes with some resin or MarineTex since they may not hold the rub rain screws well. Even if you don't fill the holes, you should shoot some caulk/sealant into the holes prior to rescrewing the rail molding.

 

[Miflinite]

Thank you all for the input. Amazingly the cap and hull are tight and sturdy with each other. I have both Marine Tex and 3M high strength filler containing fiber glass so either can be used, just don't know which would be best choice. I have had some mixed results in the past using marine tex for patching old screw holes to reuse again.
My original thoughts (hopes) were to fill in everything with 3M high strength filler, and then rub some gel coat patch repair over the top. After reading some of the posts, I can now visualize the filler being to thick to get into the back of the holes and understand the suggestions for fiber cloth backing.
Could I squirt some 5200 in the back of the holes instead of resin cloth, then use filler and top off with gel coat repair?
Will the filler marry to the 5200?
I want to repair it as best as I can, but would like to try and stick with products already on my shelf.

 

[Miflinite]

The damage is severe but as long as the 'flap' between the two open cracks is sturdy and doesn't flex, a cheap fix can be done. Just make sure the cap is tight to the hull and doesn't move when lifted or pressed.
Since the major damage is under the rub rail, you can patch with MarineTex or a structural filler as mentioned but the MarineTex will work and is fairly thick so it is less likely to sag.Yoy may need to put some sort of backer in the holes and that can be as simple as a small piece of fiberglass cloth with a thread inserted in the middle to give a way to hold the cloth 'tight'. You can apply some resin to the cloth first to help it stick (on the backside of the crack). Let it set for 30 minutes or so or until firm but not fully cured and then snip off the thread and partially fill with MarineTex (or polyester resin with a filler). When all the cracks are done you should caulk the seam with something like Sikaflex or LifeSeal. I would also fill the screw holes with some resin or MarineTex since they may not hold the rub rain screws well. Even if you don't fill the holes, you should shoot some caulk/sealant into the holes prior to rescrewing the rail molding.

The area in picture #4 started to flex (bends upward) after sanding and preparing the FG to start filling. Do i need to cut this area out and rebuild now that it flexes?

 

[Hookup1]

I would not use the 3M filler or polyester resin. Same with MarineTex. They are only good for cosmetic repairs. What you are looking at is a double layer of fiberglass - top and bottom half of the boat. Screw holes have been damaged and won't hold screws. You need a hard and strong material. See my comments above using epoxy to repair. You can skip the caulk tube - just push material in with a screwdriver, putty knife and smooth the epoxy.

I looked again at your photos. It's not that big a repair. Use epoxy, glass cloth and thickened epoxy. it's a hidden repair. Mask it off and put some plastic around the area before you start.

When you go to install the screws carefully select a drill size to pre-drill with. A little tight but not so tight you snap screws. Install a few with a hand tool to make sure you have it right. Too loose and screws will start to move and saw the holes open again.

Done right - done once!