My rusty, crusty centerboard

dlochner · May 3, 2019

Project_Mayhem said:
Does anyone have any tips for getting fiberglass to kick faster when working with small batches?

Let's start with the easy question first. Temperature determines cure time for resins, within some limits. Epoxy generally takes longer to cure than polyester, but temperature makes a difference. There should be some charts on the West System site that show cure times. A second factor is the hardener, at least for epoxy. Some hardeners are designed to set up quickly, others more slowly. Using a cold weather fast hardener on a hot day will speed up the cure.

It is also not necessary for the epoxy to fully cure before adding more layers, in fact in some cases it is better to allow the epoxy to get to gel stage and then building up more layers. Adding layers at the gel stage ensures that there will be a chemical bond between layers which is stronger than adhesive bonding.

Project_Mayhem said:
Should I grind away the rust or leave it as is?

I wouldn't worry too much about the rust. Once the plate is sealed in the rudder water shouldn't get to it and the rust won't progress. Rust is protective in and of its self as it forms a barrier to moisture.

Project_Mayhem said:
Should I use filler and cloth on the leading edge or would it be stronger if I just used cloth? The bottom of the centerboard seems to be just filler with no cloth. Should this be ground down and given a cloth shell?

The epoxy manufacturers would love it if you use epoxy and cloth as you will use a ton of it. Yes, fill it first with thickened epoxy. Add the filler in shallow layers. If you put a thick heavy layer the epoxy will go exothermic and gas which will weaken the filler and the epoxy. The epoxy will become foamy and discolored. So, fill in a little bit, maybe a ½" on a cooler day. Wait a few hours, add another ½" and so forth until it close to the final shape. Get to the rough shape and then lay up lots of glass to strengthen the rudder. If you wait until the epoxy is fully cured to add another layer, it will need to be scrubbed with warm water to get rid of amine blush.

dlochner · May 3, 2019

Project_Mayhem said:
I have had this happen before but never new what it was. Can this be used as a technique for adding volume is low stress applications?

I don't know. Somehow I think not. There are however foaming epoxies that could do the same.

StargazerP303 · May 3, 2019

Project_Mayhem said:
View attachment 164366 View attachment 164367 View attachment 164368 View attachment 164369 View attachment 164370 I knew my boat would need a bit of work on the centerboard when I bought it. It was a bit more than expected but still nothing horrible. It looks like it bottomed out and cracked the bottom of it. From there water leaked in, rusted the steel plate which expanded the leading edge. This board was replaced 10-15 years ago. As you can see the manufacturer didn't do a great job when they made this one. Lots of bubbles and voids but I dont think this lead to it's demise.

Should I grind away the rust or leave it as is? I'm trying to leave some fiberglass in place so that I can match the shape of it later. I'm guessing that I'll do it in sections. Should I use filler and cloth on the leading edge or would it be stronger if I just used cloth? The bottom of the centerboard seems to be just filler with no cloth. Should this be ground down and given a cloth shell? Does anyone have any tips for getting fiberglass to kick faster when working with small batches?

First thing is to find out "How much total weight do you have to achieve!" If you change the weight, then you change the sailing dynamics. Contact manufacturers to get your specs for your boat centerboard. The lead location is also important.
After finding this out you now can pick the material to use including adding more weight too!. I had a precision 18 and had to repair the centerboard. After I finished and installed it and put it back in the water for some reason I would heal-over way to easy. I found out the lead in the lower part was missing and didn't know it was gone. I had to add 15 Lbs of lead to the lower end and wow what a difference in performance too.
Hope this helps. Capt Rob

Chief RA · May 4, 2019

Grinding off excess rust and bad pieces seems appropriate. Heed Capn Rob's weight caution as well. Use of Bondo is fine for reforming and shaping the keel but cover it all with overlapping glass material for strength. Chief

Crazy Dave Condon · May 4, 2019

Is that an O’Day sailboat which mfg. went out of business in 1989?

Daveinet · May 6, 2019

DO NOT GRIND. It will take waay too long, and removes too much material. Use a sand blaster instead. The problem is that once it begins to rust, the metal is pitted. Trying to remove enough material to leave no pitting means you are grinding off a lot of good material surrounding the pits. If you use a sand blaster, it penetrates into the pits and cleans out the rust.
My OEM swing keel is cast iron. No epoxy, just paint. I started grinding and found it that to be impractical. I sandblasted it with a Harbor Freight sandblaster. I then painted it with Cold Galvanized paint. That was 3 years ago. There is some rust stains on the edges wear it rubs on the sand when beaching the boat, but other than that, the coating has been just fine. Once you put a zinc paint on it, you can then put a protective layer of either epoxy, or some sort of fairing putty to smooth it out.
So that is my opinion. Take it for what it is worth.

dlochner · May 6, 2019

Project_Mayhem said:
Does Bondo kick off any faster than fiberglass with filler?

Bondo is a polyester resin with filler. Do not buy the Auto Bond, they make a marine grade Bondo.

Chief RA · May 6, 2019

Dave: what difference does it make whether your filler is polyester or not? It is supposed to be covered with a fiberglass coating anyway! Fillers are all basically permeable anyway due to the curing concept. Chief

/

dlochner · May 6, 2019

Its not the resin, the resin is the same, it is the filler. The Auto filler is designed for quick smooth fairing, the marine bonds has fiberglass fibers so it is is stronger and better for filling deeper cracks and voids.

The other is issue is polyester resin does not have the same adhesive properties that epoxy has.

Chief RA · May 6, 2019

Dave: I think your nit picking. Never have seen a problem. Chief

dlochner · May 7, 2019

Chief RA said:
Dave: I think your nit picking. Never have seen a problem. Chief

Oh I might be. Polyester resin filler also shrink over time. In the attached photo you can see a line where the filler cracked from shrinkage. I was replacing the strut so some of the filler was already removed. Before I started digging into it, there was a crack that perfectly matched the molded in recess for the strut.

Chief RA · May 7, 2019

Dave, thats a high stress area! Lots of factors would need to be addressed with such a repair. Not overlaying with glass material over that is just what I stated NEEDED to be done in my 1st post to strengthen and seal the repair! That type of repair should not even be done with filler! Fiberglass layering should have been used after the damaged area had been ground out and edge feathered. Behind that mounting should be reinforced as well. Chief, IE,minor (plastics) CSU Chico Ca.

dlochner · May 7, 2019

Chief, what you are seeing is just the start of the process. The base of the strut sits in a well molded into the hull. It was a couple of inches deep. It was then set in some sort of fairing compound and through bolted to the hull. When I replaced it, I set in thickened epoxy and through bolted it. and then faired it in with several layers of thickened epoxy.

The boat is a Sabre 30 and Sabre used polyester fairing compound to fair in the strut and all the flush through hulls. After about 20 years, the resin shrunk and began to separate from the surrounding hull or chipping off the through hull fitting.