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| Tapering Battens http://www.hobie.com/au/en/forums/viewtopic.php?f=14&t=36288 |
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| Author: | BigWhoop [ Sun Jun 19, 2011 5:45 pm ] |
| Post subject: | Tapering Battens |
Question: Speaking of which, exactly how do you taper the battens? Some of the older battens that came with my '81 are flat from one end to the other, obviously done by sanding. Others are flat only from the ends towards the center but not all the way across. What's throwing me is the taper vice flattening. I have similarly "flattened" battens that I've replaced with a sander but I'm not sure how to taper them accurately and consistently if you mean thin at the ends and thicker in the middle. Answer: It used to be common to taper battens when I was actively racing a 16. I think there's a section in "Welcome to A Fleet" about tapering battens. Nowadays apparently nobody bothers. Here's what I do. If you read Marchaj he tells us that the drag increases if the draft in the sail gets back past 50% of chord (mast plus sail). The sail is cut to put the max draft around 33 to 40%, I figure to give the sailmaker a hand by giving the batten an airfoil shape and putting the draft around 40%. An untapered batten has the max draft at 50% and bends in a sinusoid so it will be too sharp a bend in the middle. I use an angle grinder, and gloves, and a mask. Start a little behind the halfway point (50%) and try for a straight taper up to the front. Leave enough material so that it fills the batten cap. I have a preference for the Trentec batten caps. Epoxy them in when you're done otherwise they stay in the pocket protectors and they're a real ... well they're real hard to get out. You need a kitchen scale or the kind you use to weigh fish. Bend the bottom batten and see how much pressure it has trying to straighten. About eight or ten pounds. Then do the next one up. I like to try for all the battens having the same tension. You have to grind more off each one until the top one, which will start at about 25 pounds and if you're trying to match will need to be ground down to 8 or so. If you have a flat top sail the angled top batten needs to be about 1.5 times as much or about 12 or 15 pounds. Lay the batten on a long flat piece of scrap and keep the grinder moving so you don't get thin spots. You want a long straight taper. You could use a belt sander but I think you'd wreck some battens, or an ordinary orbital sander but it takes a long time and makes a lot of dust. I like to paint the battens when I'm done since they have a high glass to resin ratio and put glass slivers in you when handled. Be careful. Or wear gloves. |
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| Author: | Jman6631 [ Sun Jun 19, 2011 8:17 pm ] |
| Post subject: | Re: Tapering Battens |
Hey buddy, WOW, thanks a lot. I will copy this into my revolving punch list of items to do. Very, VERY helpful, thanks! |
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| Author: | ChrisD [ Mon Jun 20, 2011 3:31 pm ] |
| Post subject: | Re: Tapering Battens |
I gave the subject some thought and trial and error this spring. I think Matt Bounds sentences in the link below sum things up nicely. I had excellent results and control using a small block plane. Shaves the material like butter. viewtopic.php?f=4&t=27174&p=112201&hilit=tapering+battens#p112201 |
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| Author: | BigWhoop [ Mon Jun 20, 2011 3:44 pm ] |
| Post subject: | Re: Tapering Battens |
Yeah Matt is right on the money. I threw in some scientific references to make me look smart.Or at least smarter. You used a block plane to taper your battens? What a great idea if it works. Lots more controllable than a belt sander. I just have trouble imagining my block plane cutting 'glass. Did you use an electric plane? I have to try this. How often do you have to sharpen the blade? |
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| Author: | ChrisD [ Mon Jun 20, 2011 4:47 pm ] |
| Post subject: | Re: Tapering Battens |
No power needed, just a small sharp back pocket sized block plane. cuts full length strips like butter with total control. Did not seem to dull the blade noticeably as I did not have to sharpen while doing the work. Try it! Forgot to mention that I did sand them lightly with 180 or 220 grit afterwards just to smooth up some errant glass fibers. |
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