written by Matias Collins on January 18 of 2005 and read by 1222
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I believe that for sailing to windward mast rake (aft) should be as great as possible consistent with sheeting the mainsail and the jib. As in strong winds the rake must be reduced - to permit sheeting the flattened main on a bent mast and tensioning the jibstay - the maximum rake should be set for light air. Select a rake that causes the mainsheet blocks to just meet in 6-8 knots which will (as discussed in the first commentary of this series) result in the mainsheet being two-blocked - but sheetable - in stronger winds as the jibstay is tensioned and shortened.
Once this rake is determined the mast base - or the deck plate on which it sets - should be modified so that the mast base sits flat on the deck in maximum rake (6-8 knot) conditions. One cannot make the rake fit the mast base angle; one must make the mast base angle fit the rake. Ths means that after trial and error to find the optimal rake the mast base must be filed or shims placed under one end of the deck plate (or something else done) so that the base of the mast stays flat on the deck while sailing.
Keeping the mast flat on the deck - resting on both its back edge (good for slacking the jibstay in light air) and its front edge (good for stopping the jibstay from pumping in heavy air) - serves two purposes:
1. It permits the jibstay and backstay to be divorced - so that one can be tensioned or slacked without the other being tensioned or slacked - so that in light air the jibstay can be sagged while the backstay keeps the mast bent to the mainsail's luff curve and so that in heavy air the jibstay can be tensioned without overbending the mast.
2. It keeps the jibstay from pumping (as the mast rises and falls) in waves.
Most boats get by without this exact arrangement because in light air and smooth water the jibstay doesn't pump anyway and in heavy air/waves the jibstay is tensioned and pulls the mast forward so that it rests on its front edge - but flat on the deck means that it is always providing the jibstay tension and sag desired - permitting the maximum jibstay sag in light air and the maximum jibstay tension in heavy air.
Forget everything I've ever written previously that conflicts - and everything you've ever read previously about these matters! Extensive recent experimentation has convinced me of the following:
<B>1.</B> The mast falls aft naturally as soon as it is raked out of column. It must be prevented from falling aft and allowing the front edge of the mast base to lift off the deck by (1) the relatively ineffective upper shrouds (only operative when the cars are all the way forward, i.e., in light air) and (2) the very effective jibstay (when it is tensioned).
<B>2.</B> Moving the upper shrouds aft reduces their tension (if the mast is properly raked) and therefore reduces lateral mast sag, but allows the front edge of the mast base to lift and therefore requires more jibstay tension to keep the mast base flat. Moving them aft has no direct effect on the jibstay tension.
<B>3.</B> Tensioning the lower shrouds reduces lateral mast sag; moving them aft decreases fore and aft mast bending and thereby slightly increases jibstay tension.
<B>4.</B> Tensioning the backstay tensions the jibstay, but the backstay is best reserved for flattening and opening the mainsail.
<B>5. </B>If you want to tension the jibstay (which also bends the mast fore and aft), tension the jibstay.
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