|Topic Review (Newest First)|
|03-23-2010 01:54 PM|
Matching forestay sag to luff hollow .....
There is one and only one tension in a forestay (headstay on a cutter, etc.) that will CORRESPOND to the 'luff hollow' - the long smooth curve that the sailmaker cut into the luff. The luff hollow is cut from the front panels to compensate for the EXPECTED sag in the forestay.
If the forestay is not precisely tensioned, then the angle of attack attainable from the sail's geometry is lessened. Same applies equally to: too-tight and too-loose.
Too loose a forestay and the angle of attack (ability) lessens, draft goes aft, and the CE .... moves to leeward !!!!!!! Result: aggressive heeling, keel begins to SKID off to leeward or minimal LIFT development, s-l-o-w-s.
For PRECISION matching the luff hollow TO the correct forestay tension:
(If you dont have the sailmakers original values of luff hollow). Take the jib and lay is on clean & FLAT ground, make a 'bifold' along the luff so that the luff section is FLAT on the ground with ALL wrinkles out of the luff section... the 'bifold' will allow the partially spherical sail to lay flat along the luff .... the mid & leech sections will have some wrinkles.
Then pull a string taught between the head and tack connection, then from the taught string put a few (perpendicular) marks all the same distance from the string well 'into' the luff. I sew down a long 1/4" wide (grey) tape along these marks .... all the way down and a few inches back from the leading edge of the luff. You can use a few 'dots' of 'permanent marker'. If you have ANY QUESTION during racing, etc. of correct backstay (forestay) tension, simply walk forward and put your eyeball near the tack of the sail a "look up" - if the added 'luff hollow stripe' is STRAIGHT .... then the forestay tension is ABSOLUTELY TOTALLY PERFECT .... and you cant get it any better because the luff section of the sail is EXACTLY at the shape that the sail designer cut into the sail. When 'looking up', your eyeballl must be perpendicular to the 'side' of the luff ... not from behind like when sitting in the cockpit.
Set the forestay tension CORRECTLY (depends on conditions, sail loads, sea-state, etc.) so that the SAG in the forestay EXACTLY matches the luff hollow hat the sailmaker cut into the sail ..... and the sail's luff shape will be fully optimized. The boat will point like a banshee, the keel will LIFT, and the wake of the boat will be coming straight out the stern of the boat, etc.
Warning --- dont overcrank on the jib winches as this will also increase the forestay sag, etc. ... if so (as indicated by the luff hollow stripe) then you need to add more backstay.
This is a simple VISUAL way to get correct backstay/forestay tension each and every time out that does not involve 'guesswork'.
hope this helps.
|03-22-2010 08:50 PM|
|Sailormon6||Send me a PM about that time and we'll try to find an opportunity to practice in light air.|
|03-22-2010 03:27 PM|
I've been having some of the same types of issues with my boat, ie in heavy air, we do pretty well, light, we get beat. A number of folks have mentioned my traveler/main sheet is too tight and the boom is too centered, along with some other main sail issues. I went out the other day with a fellow and got a few things figured out, going out sat in a 3 of 4 race series sat with another club member, and will see what else we can straighten out.
I've read the north along with any other sail trim book I can get ahold of, some works, others you have to play with it etc too. Not to put it on/in your shoes, but I have no issues looking in the mirror and realizing I/crew are the issue..........it could be you, and do not be afraid to ask for help if offered etc too.
|03-22-2010 03:02 PM|
|zz4gta||I just re-read your PM from over a year ago. I don't know if I responded to that but I would really like to take you up on your offer. Boat should be in the water mid April.|
|03-22-2010 02:22 PM|
Originally Posted by zz4gta View Post
I have sailed with one or two brilliant young sailors who understand how to sail in light air, but they are rare. Regardless of your crew’s racing success, if you aren’t getting good results in light air, then sailing in light air probably isn‘t their strong suit. If it was, you’d probably be getting better results, and wouldn’t be asking us for help. It’s possible that a foul bottom or other reason is responsible for your lack of success in light air, but I doubt it. About a year ago, I offered to sail with you on a light air day and try to help you, but never heard from you. The offer is still open.
|03-22-2010 10:24 AM|
I'm confused. I've read North's Trim book 4 times and like to think that sail trim is one of my strong points (in any breeze). My trimmer on board for those races has won his class in his boat twice, my tactician had won that event 9 times previously, and the bowman was also very experienced.
I finished fairing the keel and the barrier coat this past weekend. Maybe it was just a really crappy bottom. Or maybe my trim is really that far outta wack.
|03-19-2010 03:42 PM|
I believe Sailormon6 has very aptly summarized the situation. For a Merit 25, 13 knts is not a lot of wind. From your comments, I wonder too if you may be over trimming your Main, depriving yourself of drive and the benefit of the "slot effect", which really does matter on that class yacht.
N'any case, good luck...
|03-19-2010 02:49 PM|
Originally Posted by zz4gta View Post
You said, " Wind speed was light, over 3 days it fluxed from 4k up to 13k. Did 9 races total. With more breeze it seemed to point a little better, but still not w/ the fleet." That says you weren't sailing well in light air, and that's probably because you weren't trimmed correctly for light air. .
Read any treatise on sail trim, and it'll tell you to unstrap your sails in light air.
You said, "For some reason I thought I was using too little backstay, resulting in a sloppy forestay and hurting my pointing." Your thinking in that regard is mistaken. In light air, even when sailing to windward, the backstay adjuster should be eased more than you imply, and the jib halliard should also be eased until the jib luff is nearly scalloped. ( I occasionally crew for a friend who is a consistent winner in a very competitive fleet, and he won his class in Annapolis Race week in light air, and his jib luff was was not just relaxed, it was deeply scalloped. I probably would not have had such pronounced scallops, but it worked for him.)
In light air, you have so little air movement with which to drive the boat that you have to extract the maximum possible power from the little wind that is available. That means, as a general principle, that your sails must have the deepest, fullest shape. You achieve that by easing the backstay adjuster until the headstay has a slight catenary curve, and easing the jib halliard until the luff of the jib is at least on the edge of being scalloped. You also ease the mainsail halliard or the cunningham until the luff of the mainsail is completely relaxed. You also ease the mainsail outhaul until the foot of the mainsail is completely relaxed.
These adjustments aren't always the same in light air. When the wind is it's lightest, your sail shape controls should be their loosest. When the boatspeed exceeds about 2 1/2 kts, I start very gradually adding tension to the sail shape controls, because, as boatspeed increases, the wind can't remain attached to the surfaces of the sails if their draft is too deep.
Helmsmanship is also crucial in light air. When we're trying to get the boat to point high, our natural inclination is to steer it in that direction, just on the edge of luffing, but that's wrong. The expression that I have frequently heard is that you must "foot to point." In other words, pinching always results in the boat losing speed, and that reduces the boat's ability to point, especially in light air. If you want to sail as close to windward as possible, you have to bear off enough to maximize the boat's speed, and that will enable the boat to point higher. You only bear off slightly, until the speed is maximized, and then you can start steering closer to windward. If the boat's speed drops, then bear off again to regain your speed, and then steer close to windward again. You'll actually be sailing a slightly scalloped course to windward, but your average speed will be higher and your average heading will be closer to windward.
I also believe your pointing ability is being hurt in stronger winds by trimming your sails too tight. Your comments suggest an inclination to harden up all the sail shape controls in an effort to make the boat point, but boat speed and pointing ability go hand-in-hand. Even in 13 kt winds, you need your sail shape to generate as much power as the boat is capable of using efficiently. By flattening your sails too much for the available wind, the boat doesn't have enough power to achieve the speed necessary to point high.
|03-19-2010 02:44 PM|
|zz4gta||In light air the halyard was loose enough to just barely see scallops in the luff.|
|03-19-2010 12:28 PM|
Your halyard tension may also be an issue.. we found with Pentex jibs you needn't over tension your halyard. It pulls the draft forward leaving you with a wider angle of attack, forcing you lower to get the telltales flying.
Try easing the halyard and see if your pointing ability improves.
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