 |
 |
|
||||||
 |
 |
 |
 |
 |
 |
 |
||
 |
||||||||
| Jeurope > JDifference |  |
|||||||
|
Why Js Sail So Well  Now
it's possible to sail fast with just afriend or two as crew. After all, isn't this how we sail most of the time on a day's sail or when cruising? Rarely is the gang aboard to hold the boat down or fly a chute. Considering the realities of how we sail, the measure of a good sailboat should be how well it sails upwind and downwind with only 2-3 people aboard. The goal is VMG, Velocity-Made-Good, straight into the wind or away from the wind, considering both speed and sailing angle. Many of the modern integrated instrumentation systems can display this data, or you can use a set way-point to windward on a GPS to come up with the number. Good short-handed VMGs are when a "50-something" husband & wife jibe a J/105 (34.5 ft.) with asymmetrical through Woods Hole against the current, while others motor. Or, if you can beat upwind in steep waves doing 6.8 knots with a VMG of 5 knots in 18 knots of wind! Safe, Fast & Easy Flying one of these new asymmetrical chutes from a retractable, carbon-fiber bow sprit is a one person job. By using a cockpit-operated snuffer, no one has to be on deck when the spinnaker is flying, being jibed or doused. To jibe, simply let off one sheet and pull in the other. Downwind VMG is doubled. Result? Less motoring and more sailing. It's safer. One corner of the spinnaker (the "tack") is always secured to the bowsprit, eliminating wild oscillations. The sail has more slope to its leading edge with a center-of-effort located further forward and lower. Wind gusts lift the bow, propelling the boat forward with finger-tip control. No more "white-knuckled" round-up broaches. Speed from the asymmetrical's greater power pushes the apparent wind 30-50 degrees forward of the true wind direction. In light air and lumpy seas, the sail's added power steadies the boat. Deep sailing angles (160-170 degrees True Wind Angle) are achieved in a breeze. The luff, which is 8% longer than the straight line distance from tip of the sprit to halyard exit on the mast, rotates to windward as the sheet is eased - projecting area to the wind like a conventional spinnaker when pulled back by a pole. That Feel The new Js instill a sense of confidence, freeing one from anxieties. Even when planing at 10+ knots, one feels in total control. There's less work. Guests aren't pressured into unfamiliar tasks. Fewer orders are needed. It's more fun! Like a good sportscar, turning as if it were part of you. Not with sluggish delay. But with a smooth, even response - around crests, down waves and through crowded harbors. Mainsail only The new J's sail well flying any sail combination you feel comfortable with. For harbor-cruising or heavy winds, an unreefed main is the answer. If the boat sails 6+ knots under main alone, why bother with large overlapping jibs? Visibility is improved. The big main is a bonus for "cruising canvas" races. And, it takes one person to sail the boat. High wind mode is a flattened mainsail with open leech, achieved by tightening backstay, cunningham, vang and outhaul. These adjustments are quicker and easier than reefing. The jib can be rolled up and forgotten. 34% upwind VMG gain? Hull design, rig, sailing length and weight location greatly affect VMG. You see many cruising boats motoring upwind in both light and heavy air. Why? Not enough sailpower for light air or stability for a breeze. For example, the new J/120 (40 ft.), sailing upwind at 7.2 knots, 38 degrees from the true wind (25 degrees apparent) will have a VMG of 5.7 knots. This is 15% faster than other production 40 footers sailing 7 degrees further from the wind at 7 knots with a VMG of 4.7 knots. And, it's 34% faster than a classic cruiser doing 6 knots with an upwind VMG of only 4.2 knots. These differences are inescapably locked in by design and construction. Low center of gravity Good upwind VMGs are only possible with a low, vertical center of gravity (VCG). Top-heavy boats roll and pitch. This motion disturbs water flow around the boat and airflow past the sails, not to mention equilibrium of the crew on deck. The lower the weight of the boat relative to its waterplane, the greater the stability, the more sail that can be carried and the smoother the motion. This explains a J's smooth, stable ride through waves. The VCG is well below the waterplane. Resin Infusion Process You get what you pay for. Low VCG is achieved by light, strong construction of what's above the water. Since 1977, J Boats' licensed builder, TPI has become the highest quality production builder with the best warranties in the world. Starting with J/80. J/80 One Designs (26.25 ft.) and J/120s, and successive new J/Sprit boats benefit from TPI's innovative resin-infusion process. Their end-grained, aircraft-grade balsa-core laminates have structural GRP skins with 65-70% glass content, or the equivalent of custom high-tech, oven-baked pre-pregs. Carbon-fiber rig The best place to reduce weight is aloft. J/Sprit boats have Hall spars - the best engineered, tapered, aluminum racing spars available. They are custom-designed for J Boats, race-tested and abused to insure reliability with a good safety margin built-in. Running backstays aren't required. Checkstays, where provided, are for sail shaping or an extra margin of safety in extreme offshore conditions. For the J/120, one may select a carbon-fiber mast to further optimize upwind VMGs for short-handed cruising. These white, custom-engineered, one-piece, autoclaved spars have a Tides Marine luff track designed for low-profile and low-friction slides. The 120 pound weight saving aloft is equivalent to having two invisible 200 pound genies sitting on the weather rail to improve performance. Ballast Ratio & Shoal Draft The best place to add weight is in the keel. The closer that is to 50% of the boats total weight (DSPL) the better. A lead keel, fixed under a deep, structural molded sump, having much of the weight in a bulb at the bottom, is better yet. The J/120's ratio is 6,000 lbs/12,900 lbs or 47%. A high ballast ratio and quality construction are even more important, if you decide on our shoal draft option. A "J" with a shoal draft keel will outperform most deeper cruising boats. Before deciding on this option, consider that the need for shoal draft may be a function of speed. A fast boat, that easily sails 50 miles in a day, puts more deep harbors in range than can be visited in a year. Righting Moment (RMC)  Good upwind VMG requires good stability. A measure of this stability is RMC, the foot pounds needed to heel the boat 1 degree. Keel weight, form stability and construction quality are captured by this number. Among similar boat types, the higher the RMC relative to DSPL, the more likely that two people can sail her upwind to her capabilities. J/120's RMC is 9.4% of her DSPL. Horsepower Sails are the horses. A light boat with clean lines and good stability can carry the sail power needed for lively performance. There's no need for tall, scary rigs with heavy sheet loads and winches. Sail Area to displacement (SA/[DSPL/64].67) is a good indicator of how much horsepower the design can handle and what its speed potential might be. Look for ratios over 20. The J/120 is at 22%. Low resistance Too much weight usually means too much wetted surface (WS). Like brake shoes. The more WS there is relative to sail area, the quicker you stop. A good SA/WS ratio is critical for performance in North America's light air. Among 40 footers, J/120's ratio of 2.7 is fast. A boat with a 2.0 would be "glued". Then there's form drag. It's usually faster to be long and narrow. But only when combined with greater stability and sail power. A length (LWL) to beam (BWL) ratio greater than 3 is desirable for good directional tracking in waves. Then, oversized keel, skeg or rudder surfaces aren't necessary. A long canoe tracks, a pram spins. J/120 has a healthy 3.7:1 ratio with flared topsides. Flare slaps waves down and keeps the crew dry. Vertical-sided hulls bounce waves up on the crew. Speed rating The rated speed of most sailboats is published in the United States. A J/120 with genoa is faster than others 40'. An often overlooked benefit : speed helps you in route-planning when dealing with weather systems... YOUR next boat Why should you have to cruise on a boat with middle performances ? We invite you to discover sailing performance and quality are also part of confort, to anybody availability. |
