Reef Points for Roller Furling

[Genesis V]

As an idle sailors waiting for winter to pass I was trying to figure out my reef-points on my roller furling mainsail and furling jib to keep the sail plan in balance.
Right now with full main and full jib she sails great in light winds with just a slight pull to windward which for me is perfect. My jib is a 110% with a published data of 295 sq.ft. and mainsail of 384 sq.ft.
The ratios are I = 44' 10" J = 13' 2" P = 44' 11" E = 16' although when I calculate these ratios it doesn't quite match up with the publish sail areas as shown in the attached photo (it has in-mast furling with no extended roach as the standard main does, but the foot is extended from15' to 16')
Anyway that aside I wanted to be able to mark the foot on each sail so I would remain in balance at reef points of 20%, 40%, & 60% however there is not a direct reduction in sail area to foot length. With the main for instants when you reduce the foot (E) by 20% you are also reducing the height. (P) by 20% as it furls. And you do not end up reducing the sail area by 20% from 384 to 307 instead you end up with an area of 230 sq.ft.
Given the formula for a triangle area is "1/2 base X height" and using some hit or miss calculations it seems that to put in a reef of 20% the foot length should be reduced by 11%, 40% = 23% and 60% = 36% in my case the main foot length equivalent would be 14.25ft, 12.3 ft & 10.25ft.
Would the jib % ratio remain the same? Is there a simple formula to work this out? Will the spring come before I go crazy with trivial minutiae.

 

[PaulK]

You are thinking this out much too much. If you are rolling up your main into the mast to reef, you have the flexibility of reefing to whatever point works best to straighten up the boat and ease pressure on the rudder. It may be a 20% reef, or a 21.5% reef might work better because of the particular wind, wave, and heading situation you happen to be in when you decide to reef. Or maybe 46.2% would work best. All you really need are some reference marks - tape- on the boom at perhaps 2 or 3 foot intervals. This will give you an idea of how much reefing is needed in certain conditions, so that you can repeat the setting if those conditions come up again. It really doesn't matter if you've reefed 20% or 24%, or , so long as the boat is doing what you want it to. Trying to figure out what percentage of the sail is deployed (or reefed) will make you crazy, especially with the huge roach your mainsail has. Marks on the boom at any set interval will give you the reference points your need to know whether you need more- or less sail up.

 

[sailmaster39]

I agree with Paulk with his opinion.
Enjoy that H356.I just bought a new Ray E97 chartplotter for mine. I'm in the middle of setting that up.
Richard