Cast Iron Keel Fairing

[Shark]

My boat is a Shark 24 and has a cast iron keel bolted to the hull. These castings are quite rough and therefore contribute to drag. With my first boat , also a Shark, I would sand off the loose rust and other crud each spring, paint it with red lead primer and then bottom paint. By fall the bottom paint is mostly gone and new rust has started to break out again. My present boat's keel is also quite rough and I'm contemplating fairing it in some way to reduce drag and perhaps inhibit rusting. Some of the guys, with bucks to burn, have their keels professionally sand blasted and then epoxied etc. The result is a keel that is as slick the topsides.

I am, thinking about just sanding and grinding it as well as I can and then fairing it with an epoxy resin and filler mixture then applying bottom paint. I have no access at this time to the bottom of the keel itself as the boat is on my trailer. Perhaps I'll be able to get at the bottom some other time.

Should I treat the sanded keel in some way before applying epoxy so it won't rust underneath?

Is there another fairing material I should be using. One of my buddies used something blue from 3M that looked like a one-part body filler.


Lyman

[Tim]

Cast iron keels will always be a maintenance headache. I'm not sure there's anything that can be done that will work permanently, but you should be able to have some decent luck for a few years before any more major work is required.

The blue stuff is probably some sort of polyester filler. It's probably OK, but I'm sure epoxy will stick to the metal better. System Three now makes a specific product designed to bond metals; I'm not sure it's necessarily the right thing in this application, as it's more of an adhesive, but perhaps you could take a look anyway. System Three Metl Weld

What I would do is remove all the existing paint and filler, and grind the entire keel to clean, bright metal. Note that if you cannot get to the bottom of the keel, the chances of ultimate coating failure on the remainder will be higher, as there will always be that transition between uncoated bottom and coated sides. Just a thought.

Once the whole keel is ground and clean, I would grind it one more time immediately before the next step; you want as unoxidized a surface as possible. Just a quick scuff to clean off any newly-formed oxidation (which will be there whether you can see it or not) will suffice. Then, immediately coat the entire surface with unthickened epoxy resin; perhaps even apply two or three coats total (each applied after an appropriate cure time, of course).

Once you have a base of epoxy bonded to the keel, you may clean off any blush formation and lightly sand, then begin your fairing process with thickened epoxy fillers. When the fairing is complete, coat the entire keel again with a couple coats of unthickened resin to seal the fairing compound, then paint with antifouling as desired.

Can you obtain templates for your keel, given that the Shark is an active racing class? If so, I would say that you might as well fair the keel properly to the templated shape. Note that bad fairing could make your keel perform poorly, perhaps even more poorly than an uneven iron surface. This is not a job that you want to repeat often--it's a tedious, time-consuming, and ultimately difficult chore to get a perfectly fair keel. Lots of back-breaking hand work.

There's a guy locally who almost makes his entire living (seemingly) from fairing the keels of our local J/Boat and Etchells fleets. He does a spectacular job, but what miserable work. He is well compensated for the job...I am always staggered to find out what people willingly pay to have their keels faired. Cruising is so much easier!

I do know that properly faired and symmetrical foils make a significant difference, mostly for lift and pointing ability; speed increases from reduced drag may also occur, but these are not always noticeable. The keys to maximized sailing performance are always the foils: keel, rudder, and sails.

[George ( C&C 40 )]

Hi Shark,


I normaly don't disagree with Tim on matters boatbuilding but I don't think that the grind and epoxy method works well with cast iron. I own a C&C 40 with a cast iron centerboard and the only way we have been able to get a good seal on the metal was the following process.

1. Sandblast the keel until it is nothing but pure white looking metal.

2. While the metal is still hot from the sandblasting wipe it down and then paint the whole thing with Ospho. Use a lot and maybe do two coats in quick succession. Do not sand the Ospho coating after it dries!

3. Wait one day and then paint with unthickened West System epoxy.

4. Lightly buff the epoxy with fine sandpaper so it will accept paint or more epoxy if you need to do any fairing.

5. Apply bottom paint.


The problem I came across with the grinding method was that there are too many cracks and crevices to completely get rid of all the rust. Also, the metal is really hard. The sandblasting does a much better job and the Ospho converts any little bit of rust that's left. I got the above process from a metal finishing company in my area and it works well.


Good Luck,

George
C&C 40

[Shark]

Tim and George,

Thanks for the feedback. I guess there's no "easy" answer to this problem. Perhaps that's why some owners spend the money and have it done professionally.

I agree with your comment about the foils, Tim. I've taken care of 2 out of 3. I purchased new sails in 2003 and a custom-made mahogany racing rudder. The keel has yet to be tackled. I also need to do some work on the bottom ... 18 years of bottom paint etc.

I think an improvement in skills of the captain and crew would bring the greatest gains on the race course!! I used to do better with the old Shark but 20 years absence from the race course and stronger competition may explain the current state of affairs. Given my "advanced" years I try to be more philosophical but losing boat lengths to windward is still maddening! .... but if I didn't like it I wouldn't do it .. would I?

Lyman

[Peter]

You'll never get rid of all the rust because of the irregular surface on cast iron. I like the sand blasting idea. After that you'll need something to chemically stabilize it. I'd try something completely different: POR-15.
Check it out at http://www.por15.com/product.asp?productid=6

[Tim]

I think sandblasting is probably a better idea, but I was providing a solution that could be achieved easily by an owner without a major investment. Blasting would definitely do a better job getting into the various crevices, though. Neither method will last forever; the iron will rust again, at least in places, and the process will need to be repeated either way.

Cast iron has no place on boats, but that never stopped builders from using it. George, I remember my Dad constantly fighting with that stupid centerboard during the racing years, and having it removed and redone several times. When he stopped racing the boat and used her for cruising only, I don't think the centerboard ever came out of the trunk, even when sailing, so who knows what it might look like today!

I never thought of using one of those rust-coverter products, like the POR-15 and similar products. Those work really well in the open air on normal metal products. As long as epoxy sticks well to it, these seem like they might be an interesting choice.

Lyman, there's no doubt that skipper and crew are the most important things on the racecourse. There's a local guy here, sort of a legend, who can pretty much make any boat in which he is sailing win any race--he's just that good. A few years ago he rescued this ancient Pearson 10M from the yard, where she had been sitting for at least a dozen years, and was suddenly winning with this piece of junk. It sure wasn't the boat that made him win. That said, I believe in preparation, both for boat and crew, as a viable means of evening the playing field.

Anyway...

[George ( C&C 40 )]

Hi Guys,


Check it out I'm a registered user now!

I may have mislead when I described the Ospho as being something you paint on. It's not a paint at all. I just use a brush to work it into the surface of the cast iron. Ospho's a liquid that does nothing but convert rust to a hard black substance ( metal ) that epoxy or paint will stick to. It works really well and because it is a water like liquid it can seep down into cast iron pores well. Whenever it hits rust it foams up an converts it to metal. Very cool to watch and has great penetration. It does such a good job that it might be possible to just coat the keel with Ospho, maybe with a spray bottle since it's a vertical surface, and then epoxy or paint the keel. The only metal I would use Ospho on is cast iron, I would grind or sand anything else.

Tim, I pulled my centerboard when I got the boat last year and there was about 1/8 of solid scale rust on it. I'm sure there was more but it was getting ground off by the trunk as it went up and down. Working great now though.


George

[Shark]

Tim,

I hear you. I also believe in preparation and will continue to do so within reason and within the limitations of time and resources. Sailing as much as possible is the name of the game.

Your comment about "the guy who can always win no matter what" appears to be universal. The outcome of most of our club races is predictable to some extent just by seeing who shows up on the starting line. However, when you inquire further sometimes reasons for good performance emerge with statements like - "He grew up on sailboats like that." or "Didn't you know? He sailed on the Olympic team." But sometimes the explanations are more mystical. "How did he know there would be wind over there?"

It's a great sport and pastime.

Lyman