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lee_1999 04-24-2002 07:04 AM

How do you fair a keel?
 
I have a 1964 Rainbow 24 with a cast iron bulb keel. I''m in the process of removing all the old cracked fairing compound and then I plan on sandblasting the bare metal. I have read a number of posts regarding rust converters and epoxy primers,etc.. So, I have a good idea how to prep and cover the surface. But, I''m sort of confused on exactly how to go about "fairing" the keel. Or, do I really need to fair? Can anyone enlighten me? Thanks.

paulk 04-24-2002 06:44 PM

How do you fair a keel?
 
Racers talk about fairing their keels because they want them to be the optimum shape for the best boatspeed. They spend hundreds of dollars on templates, and then hundreds more on epoxy and microballoons to fill and sand until the shape matches the templates exactly. (The owner also provides several cases of beer for the sanding party- but not too much, because he wants a good job done, too.) Your boat probably doesn''t need such exotic treatment, but you will want the keel to be as smooth and slippery as you can make it, without going crazy. This will mean filling in any cracks or dings you come across with the microballoon/epoxy mix and sanding them down smooth, prior to repainting the keel. Make sure you use the fairing compound filler with the epoxy, not the structural filler. The first sands down easily; the latter takes forever. Wear rubber gloves and a face mask to avoid too much contact with the epoxy.

Jeff_H 04-25-2002 05:44 AM

How do you fair a keel?
 
I agree with Paul that you don''t need to go to the extremes that racers usually pursue but you should do some fairing. When you sandblast the keel the cast iron surface will have a distinct resemblance to the craters of the moon.

(There used to be a good description of the fairing process on the WEST System Epoxy Website but you may have to order their Monograph via snail mail.)

The first step in fairing is to get a well adherred first coat of unthickened epoxy on the keel as soon as the sandblaster stops. As soon as the sandblasster stops blasting, wipe down the keel to remove the dust and roll on a coat or two of epoxy. These days I am using MAS but WEST System is very good as well. (Now here is why I like MAS)You then need to wach and scrub the whole area with an 3m pad to remove the ''amine blush''. MAS makes a product that does not have an amine blush.

My favorite way to fair a keel (If there is such a thing as a favorite way to do an onerous job like keel fairing), is to use thickened epoxy and notched squeegee. There are squeegees that have 1/8" wide notches every 1/4" or so, that is what you want or need to make if you don''t find one. Typically I trowel on the thickened epoxy and then run the notched squeegee vertically so that I end up with a series of near vertical rectangular ribs. There is a point before the epoxy had completely cured (just at the end of the rubbery stage) when it is easier to cut the epoxy. Using a RedDevil, Surform bodywork plane, I plane down much of the excess material. I use a batten held fore and aft and on a diagonal to look for humps, bumps and hollows. Don''t take too much off with the plane. Once the epoxy has cured I grind the ribs down to a final faired shape.

You then need to wash and scrub the whole area again with an 3m pad (including the bottom of the grooves) to remove the ''amine blush''. When you are sure you have the shape that you want and the amine blush is off the entire epoxy surface, fill the grooves with thickened epoxy as well. Some people use a different colored filler for this because they like to slightly overfill the whole area and when the ribs show up they know to stop sanding.

Once the new filler has been ground down to the top of the ribs, check the fairness with a batten again. If there are areas that need minor attention, you can spot fill and sand just those areas. When everything is too your liking you should roll on a barrier coat and you are ready for bottom paint.
Good luck,
Jeff

lee_1999 04-25-2002 06:29 AM

How do you fair a keel?
 
Thanks Paulk, Jeff. That''s pretty much what I was hoping to hear. One more question: My bulb keel seems to be constructed sort of like a fin keel with two half bulb shaped plates attached on either side of the fin. So there is a very distinct boundary or groove where they meet. Do you think I need to fill this in and contour it? Or just stay with the basic shape of the keel and smooth it over?

paulk 04-25-2002 03:55 PM

How do you fair a keel?
 
This is the sort of thing the racers go nuts over- what is the optimum radius for any "corners"; balancing wetted surface with added weight. You will be probably be fine using your (gloved) finger to fill in and round off the joint -- like the seam between a bathtub rim and tiled walls. If you do a nice job, follow-up sanding will be mimimal. Theoretically, you don''t want any hollows or grooves that would cause water to eddy around in them and slow you down. You''re asking all the right questions. Now it''s time to get to work so you can go sailing!!!

lee_1999 04-26-2002 06:07 AM

How do you fair a keel?
 
Thanks Paulk. You''re right! Time to get the work done and on with the fun stuff!


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