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Go Back   SailNet Community > On Board > Gear & Maintenance > Mainsail shape
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Thread: Mainsail shape Reply to Thread
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Topic Review (Newest First)
06-25-2010 01:26 PM
jackdale Luff tension will have some bearing on the depth of the draft, but outhaul tension and mast bend will have a much bigger impact.

A slight aside - use a knotmeter to verify speed changes. It will show an immediate response, the GPS shows an average speed between fixes.

Also - if you do re-cut your sail, go with a loose footed main; there will no friction, other than the outhaul car.
06-25-2010 12:57 PM
Gary3675 Does the Sail have a flatting reef? An eye 6 inches to a foot up the leach of the sail. WE had a Columbia 26 growing up and our foot was baggy until we put the flatting reef in.
Do you have a picture?
06-25-2010 12:47 PM
RichH "One of my problems is that the sail slugs along the luff, and the one at the clew offer a huge amount of resistance themselves, they kind skitter their way up - it's like trying to torque a bolt with a bunch of crap on the threads, the torque wrench will be clicking well before the bolt is where it needs to be, I need some low friction type of slides."

Clean out the mast/boom tracks, and then either 'rub on' some paraffin candle wax or a dry sail track lube such as McLube, etc. Putting a small carved 'pencil' of paraffin between the two topmost slugs will help insure that the track gets 'lubed' every time you raise/lower the sail.
06-25-2010 11:14 AM
deniseO30 put some lubrication in the track, it will help. don't forget the topping lift again.
06-25-2010 11:02 AM
Gorlog Thanks for the input, I'll try not to bear down on the sail so much. And yes, the sail is indeed attached to the boom with it's bolt-rope sliding through a track on the boom, and yes, the sail definitely maintains maximum draft right down to the foot, it just seems a little excessive - I will post some pictures after my next sail. One of my problems is that the sail slugs along the luff, and the one at the clew offer a huge amount of resistance themselves, they kind skitter their way up - it's like trying to torque a bolt with a bunch of crap on the threads, the torque wrench will be clicking well before the bolt is where it needs to be, I need some low friction type of slides. I'll try adding some tell tales (it needs it) and will verify speed changes in relation to trim changes with the GPS. I do want to get maximum performance, and I'll keep trying until I do! As always - thanks for the tips
06-25-2010 09:53 AM
JimsCAL As mentioned, make sure the topping lift is not too tight. It should be slightly slack with the mainsheet and traveller pulling the boom onto the boat centerline. If tight, loosen it. Note there should be some shape at the foot. Flat is a relative term in this case.
06-25-2010 01:52 AM
RichH
Quote:
Originally Posted by Gorlog View Post
I had the outhaul as tight as all the strength I could muster.
Thats your problem !!!!!!!!! youre not sailing, you're testing the ultimate tensile strength of the sail material, and are your're not 'shaping' the sail to get the 'optimum' out of it.

If you take ANY piece of cloth and *overstretch* it along any 'edge' it will by 'bias realignment' of the fibers form a large CREASE (on a sail called a 'girt') close to that edge. ...could even look like a full baby diaper.

You dont state if the foot is attached to the boom or if its 'loose footed'.
A mainsail that cut for slugs or 'boltrope' attachment to the boom will usually have EXTRA material added to make a smooth 'connection' between the 'working' lower panels for the intended purpose of allowing sufficient draft in the bottom panels. This is called a shelf-foot and allows for maximum draft along the foot of the sail and 'closes the space between the 'working' part of the lower panels to the boom - the thought being that the shelf foot would prevent 'short circuiting' of the air from high pressure (windward side) to the low pressure (leeward side). Without the shelf foot, the sail at the foot section will be very FLAT.
A loose footed sail doesnt have any cloth between the boom and bottom panels.
Both configurations are equal aerodynamically, the loose foot easier to shape the bottom sections.
Both configurations can be permanently deformed by too too much tension on the outhaul, etc.

Putting all the strength you can muster in ANY sail shape adjustment is a sure-fire way to permanently deform the sail ... the sail material will exceed it elastic limit and will soon be permanently stretched out of shape.

Flat sails are for 'speed' -like 'high gear' on an automobile.
Full drafted sails are for 'power' to punch through waves - lower gear.
Neither shape will ensure that you will be at optimum when beating !!!!!!!!

You need to carefully shape the sails in comparison to 'some metrics' to get the most out the boat ..... eg. making any trim/shape adjustment and then checking with the SPEEDO to validate if that change of shape or trim was beneficial or not. When beating, reaching or broad reaching a more prcise 'instrument' to qualify the 'metrics' is a GPS with VMG (velocity made good) function. VMG will optimize the boat speed AND the BEST course angle of the 'beat'.

For each and every combination of wind speed and wave condition there is ONE and ONLY ONE 'shape' that is optimum. If you arent using a FULL set of tell tales so that you can at least visualize if the 'shape' is working well\ ... you are only guessing. A FULL set of tales is: Mainsail - midcord and leech; Jib - luff & leech ... and a ROW of 4-6 tales about 1/4th the way up from the foot to ensure that you are STEERING correctly to keep the precise angles of attack.

Beating optimization comes from
1. The sail plan *shaping* is controlled by observing the tell tales .... the BEST ever method of sail shaping via tell tales is ArvelGentry.com ---->magazine articles -----> and then 4 articles of a series: Checking Trim on the Wind, ---> Achieving Proper Balance, ---> Sailing to Windward, ----> Are You at Optimum Trim?
Only after you get near perfect shape and trim ... then will sail close hauled like a banshee ..... and the sails will be near perfect shape simply by using the tell tales and the SPEEDO (or VMG).
2. a very balanced helm with very little 'weather helm', a rig that is properly tuned so that the forestay with jib attached and windloaded .... doesnt sag off to leeward. Eg. optimization includes absolutely correct backstay tension so that the leading edge luff shape that the sailmaker cut into the luff is EXACTLY matching the 'expected sag' in the forestay for the conditions present. Once the rigging in near perfect 'tune'/tension - the forestay sag is controlled by the backstay tension.
If the mast is raked reasonably well, the way you control weather helm is to adjust mainsail halyard or cunningham tension .... more halyard tension moves the position of maximum draft more forward and flattens the leech sections and vice versa.

Guessing or following 'rules of thumb', ancedotes, etc. ... sorry that wont get you anywhere but slow, overly heeled, skidding off to leeward, overpowered, underpowered, 'cranky' or 'dull' boat ... etc. Shape and trim based solely on a full set of tell tales. Any time you adjust the tension on ONE side of a sail, you usually have readjust the tension on the opposite edge of the sail, verify each change with the speedo (or VMG). When sail shaping, always TWO adjustments, never just one. Anytime the sail is showing 'girts' ... you are 'over-tensioning' something.


If FLAT sails were the choice for beating .... we could use plywood sheets instead of sails.
If you have to gorilla-tension a sail to get the proper optimized shape .... it needs to be taken to a sailmaker for a 'readjustment'. :-)

Hope this helps.
06-25-2010 12:08 AM
jackdale Re-reading your posts I am beginning to think that your have a "bagged out" sail that might need re-cutting or replacing. Consider having a sailmaker look at it.
06-25-2010 12:00 AM
Gorlog What do you mean by hard?
Hard to pull - yes, indeed, I actually have to grab the end of the sail to help it along. Oh and thanks for the tip on loosening the vang and mainsheet, I think I had done that, but I'll make a point of it next time
06-24-2010 11:55 PM
jackdale How hard is your outhaul?
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