Cast Iron Keel

[neoxaero]

My Santana 21 has a solid cast iron keel on it. The keel along with the swing keel portion are in okay shape (solid) but its far from smooth. I imagine the effect of this drag is causing me to lose some speed - especially on the light wind days so common in the summer in central texas.

I have a sandblaster so I was planning on sand blasting the keel to remove the rust and follow the sand blasting up with a good primer to keep the rust from returning.

Next I would like to put some sort of filler on the keel to smooth it out as much as possible. I've done a fair bit of automotive body work - but Bondo filler wouldn't work here since it absorbs water like a sponge.

So what options do I have to smooth this thing out? My end goal is to paint it up with an ablative bottom paint so I can leave it in the lake over the summer.

[Gene T]

Epoxy thickened with a sandable filler would be my choice. Microlite 410 maybe.

Sounds like you are on the right track.

Gene

[Faster]

There are epoxy based fillers like Epifill that are not too hard to sand out, and are not hydroscopic like bondo. Cost more, though (of course!)
Interlux also makes something similar. If you get down to clean metal and immediately seal it you should have good success, and you're sure to notice the improvement once it's all faired.

[tjvanginkel]

When we had the rusting cast iron keel of our Columbia 26 barrier coated the yard took it down to bare metal and then put heaters on it for 4 or 5 days to dry it out before it was faired and coated. I don't know if that was for the fairing or the epoxy barrier coat or perhaps for both. It might be something to check out. May be not an issue if your boat is not in the water all the time. It did make the boat go way faster having it smooth! Of course it helped that we took off years and years of flaking lumpy bottom paints and made the rest of the bottom smooth too. Oh those previous owners....
Regards,
Tanya

[olson34]

Once that iron casting is cleaned shiny, you have a limited window of time, like under an hour to seal it from contact with oxygen.
A friend of mine used to run a repair yard and had the best result by using a stiff wire brush head on a slow drill motor to "abraid in" wet epoxy right after the final cleaning/degreasing of the keel. A Wee Bit messy, and of course the wire brush was tossed out. He said this would last many many years before the inevitable return of rust spots.
Iron keel castings are a lot cheaper/profitable when building boats, but as you are finding, there are big costs passed on to all subsequent owners.

LB

[BigZ]

In a similar case, I used an angle grinder and other weapons to clean up my cast iron keel. Then used POR 15 as the first coating. The POR stuff doesn't seem to care if there is some rust on what it is covering, so it seemed like good stuff to use when the timing couldn't be controlled. Do a google for them, some automotive paint suppliers will stock the stuff.
After the POR I used west epoxy and the appropriate filler to smooth things out. Sand, repeat, sand, repeat, etc. Then a final couple of coats of unfilled epoxy just for kicks. Lightly sand, repeat, etc.
It's only been two years, but the repaired areas show no sign or recurring rust.

[neoxaero]

I've used POR 15 for a few other things before and i very well may use it again for this application. They have a product that is excellent at removing/coating rusted motorcycle gas tanks. I need to look into it more and find exactly what to use. I'm hoping to do the keel this weekend and start sanding the bottom of the boat to paint next weekend.

I'm still up in the air on what to do to the bottom. I keep the boat on a trailer so i dont really need an ablative bottom paint.. and a smoother finish would definitely help on those light wind days.

[MooreVOLS]

If you want to get really smooth they make a very fine glass bead filler that you mix with expoxy. I have used this to smooth out carbon fiber before painting. It is very light and creates a perfect finish when done correctly.