I got a question via email on one of my posts. I'm just arogant enough to think my reply worth posting. The question concerned using a fishing scale to measure batten stiffness.



Seems like a lot of tuning and thinking, right?



Consider this: Your mainsail is your engine and carburetor and gearshift all in one. It's your gearshift when you flatten it; you're trading power for speed, just like in a tranny. It's a carburetor in that the right mix of heel-to-drive will give you the most power. And obviously, it provides most of the power, so it's the main engine, too. Whether you're engineering a racecar for speed or a luxury car for smooth powertrain performance, you tinker with those three things most. Sure, tires, shocks, bearings, etc. all play a role, but if your engine's poorly tuned, you aint goin' fast no matter how much grease you put on the wheel bearings. If you can't shift smoothly you aint gonna be comfortable in your cruiser either, no matter how much power steering you've got. Poor carburation produces a range of problems on a sailboat, from erratic engine output across different speeds to just plain no power at all while heeling mightily. So clean, parallel hulls, smooth rudders, appropriate mast rake all play important roles, and a problem anywhere on the boat can obviously slaughter your performance, but that performance is produced in the first place by your mainsail. If you're not producing it, all the "clean boat" tricks in the world can't protect what isn't there.



And your battens are an integral part of translating the forces acting on the sail, (through the bolt rope, tack, clew and head) into proper shape for carburation, gear shifting and power. Just one example: Batten stifness, tension and taper affect how much your sail flattens in response to, for one thing, your mainsheet. While you're sheeting to get just the right twist in the mainsail for a given point of sail, your battens are big contributors to how flat your sail gets in response. When you're going on a reach, you usually need moderate to slight twist, to get both top and bottom tell-tales flying. At the same time, you need moderately to mostly flattened main, for speed. You can and should regulate this with your downhaul, but your mainsheet does much of this automatically, while you're sheeting moderately or harder for proper twist. When you point high, you need pretty near most flattening, and usully, you're sheeting hard, for very little twist, which also flattens most. Again, downhaul and clew are important flattening controls, but the mainsheet does some of this automatically. If your battens are cooperating. Those same battens will help translate downhaul and clew adjustments to proper draft, too.



Okay, end of sermon. Here's what to do. I got this from Rick's book, "Catamaran Racing: For the Nineties" (buy this book, racer or not!) and then Randy Smyth independently suggested the same process.



Pick up one of those thingies you hold in your hand and hang a fish on, it tells you the weight of the fish. It should set you back all of five dollars.



Take a batten, stand it upright, hook your scale over the top end and pull down. The initial, highest reading is the initial bending load. Opinions differ on how much is right. Sails differ as to how much is needed. My sailmaker specified 9,6,4,3,2,2,2; working down from the top batten. Your mileage may vary. Actual California mileage will be substantially lower.



Then place the same batten upright against a straight piece of wall. Pull down to "bow" it. Holding about 6" of tape measure extended in your other hand, measure from the batten to the wall. Move the tape up and down to find the point of max draft. Straighten out the batten and measure the distance from that point to the luff(skinny) end of the batten. Then measure the whole batten, and divide the smaller number by the larger one, yielding a decimal. Convert the decimal to a percentage by moving the point 2 places to the right. It you've got tapered battens, your percentage should be under 50%, if you do all this right. Un-tapered battens should come out pretty darn near 50%. Consult knowledgeable parties whether it's class legal and/or apropriate to taper your battens. I use a belt sander, outside, on a windy day. (Use duct tape to remove tiny stickers of fiberglass from your skin.) Get advice on how much to take off, and how gradually to taper. It varies with the material and shape of battens. Some you shave the edges, some the sides. I'm not qualified to advise on all or even most types. Maybe somebody with more experience will jump in.



My sailmaker specified 40% draft, meaning that the curve is deepest only 40% of the way back from the luff. Again sails and opinions on this vary. Rick White suggests bottom battens need a greater %age than top ones, due to the need to keep the slot open. Randy Smyth didn't seem too concerned with this point. Randy did say that not all 40% draft battens have the same curve, though. Watch out, he cautions, for too-flexy tips; they can make a "Knuckle" in the sail's profile, right behind the mast. The shape of the curve in your sail is important to keep the flow of air smoothly attached to the entire sail. Which in turn matters because it's key to getting all the power with as little drag as possible. So, generally, you want a finer exit (leach) than entry (luff) because the exit is the low-pressure end, and consequently, more prone to detachment. Where the luff is pushing into undisturbed air, it's comparitively more likely to remain attached. So getting the most draft with the least detached air means putting the draft a little forward of the middle. How much forward? That's what your sailmaker does, and your draft percentage is how you help him out.



Incidentally, the tremendous importance of keeping the entire width of your sail attached to the air is also why I believe Rick advocates the uses of tell tales about a foot forward of the leach, to sheet by. Set the lower ones with your traveler, and twist in the uppers with your mainsheet. Set your flatness by the ones in the luff, using clew and downhaul. And the ones you need to care about most are the ones on the other side of the sail, to leeward. When they act up, you're stalling, which is like, literally 2 times more costly than luffing. Let out the sail or point higher until they flow and ones on your side are just about to act up.





Sail fast,



Ed Norris