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General Sail Trimming

Started by Rascl, 20 Jul 2015, 07:30

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I have been reading the online tuning guides and intend to get to some coaching sessions - but to keep me going can anyone help with below?
Mast bend. I still dont really understand how bending the mast - de powers the sail - is there a simple explanation . also when i tension the mast ram - it pushes the mast bottom back aft - i thought this put bend on the mast but I dont think it does from reading the tuning guide? it seems taking tension off the mast ram puts bend on it ...seems the wrong way round to me ? wording in txtx says increase stay tension and take off mast ram tension to bend mast. But the ram when tensioned pushes the bottom of the mast from forward to back direction of the boat
Kicker - I generally have this loose on when reaching or running then tight when beating to wind . It seems to me the kicker does little when beating to wind - but its main use is to keep the boom down when reaching or running . I am just using rule when i  use it to make sure top batten is parrallal to boom.
thanks for any help and great forum
James N3247

Antony (Guest)

It might be worth picking up one of the more general dinghy racing books for a read.  Most of your questions are not particularly N12 specific.
1.  A sail has a natural 'fullness' built into it when made.  Think of this as the camber in the sail.  If you let the mast bend, so the middle is forward of the bottom and top, then this stretches out some of this fullness and so the sail is flatter - less powerful.  
2.  Answer 1 means that you are correct that letting off the mast ram lets the mast bend forwards at deck level and above, and so flattens the sail.
3.  Most 12 sailors use quite a lot of kicker upwind.  As soon as there is enough wind to be both on the side the boom is basically held down by the kicker and moves sideways with the mainsheet.  In very light weather you might have the kicker looser and so pull down on the mainsheet in the puffs and ease it up in the lulls - so keeping the leach open.  Downwind you are right to have less kicker - in general - and to make sure that the top leach streamer is flying happily (but not too happily).
Feel free to ask more questions...


Find yourself a laser sail and lay it on the floor - it will lie flat, but the tube where the mast goes is bent - halfway up is further forward than the top and bottom.  A laser sail is quite simple but perfectly demonstrates the effects of 'luff curve'.  As the mast is inserted, the luff is forced straight, pushing the excess sail material backwards and so creating the curved sail shape required.  By bending the mast you reverse this process, reducing the depth of the sail.  A N12 (and many other boats') sail is more complex, it has some inbuilt shape and so won't go completely flat, but the effect from the curved luff will still happen.
Remember that the mast bend should be such that halfway up is further forward than the top, so tensioning the ram straightens this.
Even if you are not a tinker, it is always worth checking your mast's 'pre bend' - the bend with the rig tensioned (i.e. jib up) but no main sail up.  At first we had a forward-bent mast until this was pointed out at a N12 training day and suddenly the boat was much better.
N3162 (Baggy Trousers) "Bicycle Clips"
N2709 (Paper Dart) "Goose Hunter"

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