Mast rake: explain please!

Here is Dr Gismo’s explanation from the FD fleet-
http://issuu.com/ifdco/docs/bulletin156?e=4847973/3554503     Page 17/18
To summarise, raking-
1.     Reduces heeling force
2.     Reduces overlap between genoa and mainsail. This depowers the genoa. Especially relevant to the FD where the genoa is over 80% of the mainsail size.]
3.     Lifts the bow by a small amount. [I bet that one is controversial.]
4.     Has a tendency to automatically adjust to the correct point of sail in the gust/lull sequence.

Originally posted by RS400atC Originally posted by Oatsandbeans RS400 -the thing is that people dont generally change the spreader settingswhich the only other rig control that will affect the mid and upper mast bend. Most people have their spreaders bolted up to the standard settings and they stay like that.. So the raking does it for you simply. Gives you more mast bend and balances up the boat as it changes from "point "mode in light to medium to "fast " mode as the breeze builds. Mike Holts comments are interesting and it reminds me of what we used to do a bit in 470s. The mast bend / rake effect can be too much as when the mast is in a heavy weather setting it can now be overbent and the rig needs to be stiffened up by the spreaders being moved forward. This is now a complete pain as it involves getting up the mast to do it-just possible on a 470 by standing on the spinnaker pole fitting but not possible on lots of other boats with higher spreaders( or shorter crews). That's just a case of none of the controls in a typical rig being independent, we can't adjust rake without changing the effect of the spreaders.But raking also works on a yacht with inline spreaders, or on a Solo with no spreaders.

On an RS400 unless you lengthen your jib halyard you aren't taking you are just increasing the prevent in the mast. I think you are getting confused between the effect of rake and pre-bend.

Originally posted by craiggo In light airs the drag from such a swept configuration is larger than for a more upright, untwisted configuration hence why it always pays to go upright in the light.

Craiggo - I followed the conversation between yourself and MM quite well.  But I still can't see a convincing answer to the question "If raking a mast creates such beneficial up wash why don't we rake the mast at all times?"  I get that an untwisted configuration creates less drag, but surely this holds true in medium winds as well as strong winds?  The Jib will always benefit from additional up wash as it is always swept back.  I can understand that raking the mast further creates a more swept back plan for both jib and main, creating more up wash at the top of each sail, allowing you to twist the tops of the sails and apply more forward drive than lateral drive.  I just can't for the life of me understand why this would be more beneficial in heavy air than medium (max power) air.

Just get a Laser, they all have the same mast rake. Especially the red ones.

I think that there is a bit of confusion here about, shroud length ( pin hole), jib luff length ( tensioner position), rig tension rake and bend. If the shroud pin position is changed by say 10mm down and the rig tension is kept constant the jib luff tensioner will have be at a setting 30 mm further off to get the same tension due to the geometry of the rig. This will give a rake increase of 75mm . and a prebend increase of 20mm. (The numbers are approx. from memory). Just changing pin position and keeping jib luff the same will have big effect on the rig tension but only a small effect on rake. That is why a rig tension guage is needed ( to ensure that is constant) as are calibration marks on everything you can to make sure that you have under control. ( another point is that dropping off the rig tension a bit will have a big effect on rake but only a small effect on rig tension)