Seeking Suggestions on Rudder Repair

[GorillaToast]

Hi All.

I'm interested in opinions on the best way to make a repair to the trailing edge of my rudder. This photo shows the damage.

After grinding away the loose stuff, I am thinking of using Marine-Tex to fill and fair, then applying a layer of fiberglass cloth wrapped around the edge with an inch or so overlap on both sides of the rudder. Then a couple of layers of resin with filler, faired and sanded. My biggest concern is that the edges of the cloth will be against the flow of water over the rudder, and that in time a gap may open and the whole repair come loose.

Is that a realistic possibility, if the glassing is done properly? Or am I over-thinking it?

Thanks for any suggestions.

[Mark Johnson]

If it is a solid core rudder, and not splitting... Prep the area, then I'd use West resin and Silica thickener, build up the gouge, and sand the excess exactly fair with the rest of the rudder. The wrapping of the back edge is both hard to do on such a tight radius, and would have to be 98% "ground off" on the sides, to keep it fair. This is important.
Mark

[Mi2ndWind]

Without knowing how long that actually is, but it looks rather small, my suggestion for a quick and strong repair would be to grind off any loose gel coat, clean it out with alcohol, then fill the damaged area with milled glass or cabosil thickened epoxy. The whole repair could be done in one shot with peanut butter thick epoxy. Then grind fair and repaint the rudder, or just the repaired area if you prefer. I would avoid Marine Tex for this kind of repair, as I find it to be brittle and easily damaged for thin edge areas. My preference is MAS, but West Systems is equally good and probably easier to find. That damage looks like it's the result of repeatedly coming into contact with something though, and if that isn't resolved the damage will eventually happen again. Good luck and let's see it when you're done!

[mrm]

^^ what Mark said, with maybe a slight modification. If I am not mistaken, Silica thickener will not provide much structural strength to the mix, if any. Short lengths of glass fibre as a filler would provide strength and a mix with resin is not that difficult to sand to shape. Wear respiratory protection when sanding.

Edit: Mi2ndWind was typing faster

[GorillaToast]

Originally Posted by Mi2ndWind

That damage looks like it's the result of repeatedly coming into contact with something though, and if that isn't resolved the damage will eventually happen again. Good luck and let's see it when you're done!

That damage was done before I bought the boat, so I have no idea how it was done. Since the boat was stored for several years, I'm guessing someone dropped the rudder.

Good suggestions. I'll forego the Marine-Tex in favor of thickened epoxy.

[PAR]

Silica thickener will not provide much structural strength to the mix

Silica will add tremendously to the physical attributes of an epoxy matrix. Combined with milled fibers and/or cotton flock (West 403) a very tough, dense structural filler can be had, particularly in compression, peel and elongation qualities.

You could build a dam of sorts with tape, cardboard, etc. to save some fairing time too.

[Wand]

And on the OP's query re adding fibreglass cloth...

...as the other posts have implied but not specifically said, you don't need it; it won't do anything good or useful.

[GorillaToast]

Originally Posted by PAR

Silica will add tremendously to the physical attributes of an epoxy matrix. Combined with milled fibers and/or cotton flock (West 403) a very tough, dense structural filler can be had, particularly in compression, peel and elongation qualities.

You could build a dam of sorts with tape, cardboard, etc. to save some fairing time too.

Not sure I understand this. Where would I build the dam with tape? Wouldn't blending (fairing) the epoxy out with an old credit card while the mixture is still liquid be easier than sanding down a hardened ridge (dam)?

[s/v Jedi]

On the bigger photo I can see a gap between laminate and gelcoat. It looks like a lot more will come off. Also, the edge shows as two laminates glued together. Over time, water might have gone in there (I see a darker colored spot) and the joint might be weak or even compromised.

I wouldn't oppose some fiberglass at all. Buy some 2" wide fiberglass tape. Draw lines at 1" from the edge on both sides and grind gelcoat off. Now you have room for the tape: epoxy it around the back edge and fill up the weave. You can use a little cabosil (=colloidal silica) for filling up the weave but not for the initial wet-out. After that, fair it using a fairing filler and some white pigment. Coat it with un-thickened epoxy with some white pigment. You still need to paint the (any) epoxy repair but the pigment gives you some time and makes the paint job easier.

cheers,
Nick.

[Bash]

+1 on not using Marine Tex, which is more of an epoxy putty. What you need is slightly thickened epoxy.

I can't tell from the view provided whether the trailing edge of the rudder is actually dented. If so, I think Nick's proposal makes a lot of sense.

[capngeo]

I would grind back to good substrate, fill as required, cover with a layer of tri-axial the full length of the edge, smooth, fair, and seal with a barrier coat, then paint with antifoul. Use ONLY epoxy, as the secondary bond properties are best! Perhaps more work, but that repair will be PERMANENT!

[s/v Jedi]

Originally Posted by Bash

I can't tell from the view provided whether the trailing edge of the rudder is actually dented. If so, I think Nick's proposal makes a lot of sense.

click the photo for the big version :-)

Originally Posted by capngeo

I would grind back to good substrate, fill as required, cover with a layer of tri-axial the full length of the edge, smooth, fair, and seal with a barrier coat, then paint with antifoul. Use ONLY epoxy, as the secondary bond properties are best! Perhaps more work, but that repair will be PERMANENT!

Exactly. Same as what I posted I think?

cheers,
Nick.

[GorillaToast]

Wow. Glad I waited a few days after starting this thread to start the repair. As more opinions keep coming in, the repair seems to get more complicated.

Unless there are opposing viewpoints to Nick's suggestions, I'll likely go with that.

[PAR]

It was assumed that the repair would be ground back to solid laminate. It's also assumed that it will be feathered back at a generous slope, to tie the old work to the new. These are standard repair practices and covered in the downloadable user guides from the major epoxy formulators (west System & System Three).

Nick's repair sounds reasonable, though skip the white pigment, you don't need it under paint. Also triax is way over the top for this. Again assuming the area is sound, milled fibers in the thickened mixture, will offer the matrix elongation properties for a tough repair and cross like to the old work. Cloth if you must, biax if your anal. Silica alone tends to be stiff and doesn't have the adhesive properties that you may desire. Milled fibers with the silica will dramatically improve the adhesive attributes of the thickened mix.

By a dam, I mean you'll have a side working against gravity unless the blade is removed and you're working on a bench. If this is an in the field repair, taping up one side so the thickened mixture can't sag out, can be helpful. What would be more helpful, is applying Mylar sheets on each side of the blade, just after the thickened goo is packed on. Roll out the Mylar sheets and you can have a perfectly smooth, nearly fairing free surface when the goo cures. Then prime and paint as desired.

[GorillaToast]

Originally Posted by PAR

By a dam, I mean you'll have a side working against gravity unless the blade is removed and you're working on a bench. If this is an in the field repair, taping up one side so the thickened mixture can't sag out, can be helpful. What would be more helpful, is applying Mylar sheets on each side of the blade, just after the thickened goo is packed on. Roll out the Mylar sheets and you can have a perfectly smooth, nearly fairing free surface when the goo cures. Then prime and paint as desired.

Now I see. It is on the bench. Where does one get mylar sheets? The local fabric store, or just buy and pop a couple of birthday balloons?

More ideas than I expected. Still more to come? Maybe I should wait another week.