Common formulas and rules - SailNet Community
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post #1 of 19 Old 09-27-2011 Thread Starter
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Common formulas and rules

I am looking for a collection of formulas and rules such as determining:
Sail percentage (ie 50% jib)
L.O.W.
VMG or what to do when:
Winds light, sails flat
Telltail breaks first, fall off
Etc, etc. I'm really excited about this forum and was hoping some savvy sailor may have this cheat sheet. If not, maybe we can produce one.
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post #2 of 19 Old 09-27-2011 Thread Starter
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No takers yet. I'd settle for the means to discover the % of a sail, ex. a 110% genoa. Maybe I shouldn't be so lazy and compile my own cheat sheet, right?
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post #3 of 19 Old 09-27-2011
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Try one question at a time.
The 110% is relative to the LP (luff perpendicular) measurement to a boat.

For instance a 100% jib on a boat with a "J" dimension of 10' will have an LP measurement of 10'. A 135% on that same boat will have an LP of 13.5' and a 155% will be 15.5'. The LP is measured from the clew (usually the intersection of projecting the leech and foot edges) to the luff of the sail. The shortest measurement will be a 90* angle (from clew to luff) and you correct LP measurement.

Headsails are also refered to as
#1 (150-155)
#2 (130-140)
#3 (100-110)
#4 (75-90) sometimes called a blade or storm jib.

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Last edited by zz4gta; 09-27-2011 at 08:09 PM.
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post #4 of 19 Old 09-27-2011
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As for a cheat sheet

When in doubt, let it out.
Speed first.
Flat-ish is usually fast
Always have fun
strb over port
Stay on the boat
reef when you first think of it...
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post #5 of 19 Old 09-27-2011 Thread Starter
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Thanks, and sorry. I'm new to the site and unfamiliar with the pace. I have a library of books, each has formulas and rules, I'm looking for a list of sorts, maybe need to make it, that is portable and can be laminated to have onboard. Just quick hits, maybe reference to the details.
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post #6 of 19 Old 09-27-2011
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Apparent height of wave (AHW) divided by two equals real height of wave.

AHW * 4 = height of waves in stories told at YC bar.

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post #7 of 19 Old 09-27-2011
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Theoretical hull speed (displacement boats)= 1.34 X sqrt LWL

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post #8 of 19 Old 10-07-2011
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Here are the formulas for the Angle of Vanishing Stability:

http://SailBerkeley.com/web-resource...hing-stability

Sailing Instructor

Last edited by SailBerkeley; 10-07-2011 at 05:46 PM.
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post #9 of 19 Old 10-10-2011
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"Stupid Human trick":

Hold your clenched fist, thumb on top, at arm's length.

Your fist, from little finger to thumb, describes an arc of ten degrees.

So each knuckle is two degrees.

Sun etc move 15 degrees per hour, so one 'fist' is 10/15th hour, or 40 minutes' worth of celestial movement. And each knuckle is 8 minutes.

Now you have a quick way of telling how long til sunset. Or, if you rotate your fist to measure laterally, how many degrees that other guy is off your bow.
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post #10 of 19 Old 10-11-2011
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It feels 10degrees colder on the water tha on land - dress appropriately
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