We have previously discussed taking care of ropes, but, how long should these ropes even be? As previously mentioned, ropes are an essential element of your rigging system, and optimising your running rigging lengths is important.
Why is it imperative to have the correct lengths for sheets and halyards?
Obviously, too short a sheet or halyard does not get you anywhere. A rope that is too long increases the chances of getting tangled, adds to the overall weight of the boat and it’s just a waste of money!
Length Calculations and Formulas
You have chafed through a sheet / halyard, on your holiday, and need an emergency replacement shipped to you. How long should your new line be?
Standard sail-maker I.J.P.E. dimensions are usually the most commonly available data to work from. The following diagrams and formulas will then help calculate the most appropriate length for your ropes.
Don’t worry, this isn’t complicated maths, or rocket science. However, please do bear in mind that these are measured in metres, thus all rope lengths (results) are defined as such.
P: Mainsail hoist length
E: Mainsail foot length
I: Height of the forestay above deck
J: Length from mast to forestay
Y: Distance from halyard winch to mast
X: Distance from genoa winch to mast
Z: Height of boom above deck
L: Boat length
Ig: Height of Inner Forestay above deck
Isp: Height of spinnaker halyard above deck
Py: Mizzen hoist length
Ey: Mizzen foot length
Source of Diagram: North Sails
From this rig geometry data there are some basic formulae used to derive running rigging lengths.
Example
IJPE Formula applied for Beneteau First 40 (Source of boat data: Sailboatdata.com)
L= 12.24m
I= 16.05m 
P= 15.57m
J= 4.60m
E= 5.39m
Main Halyard 1:1 (Winch on mast) = 2.1×P+2
Therefore = 2.1x15.57 +2
Main Halyard Rope Length= 34.70m
Gennaker Sheet= 2.5xL
Therefore = 2.5x12.24
Gennaker Sheet Rope Length= 30.6m
Safety Margin
Each of the above formulae includes some room for error however, if in doubt, it is always better to add on 1-2 meters than try to cut it too short!
Conclusion
Rigging systems must have accurately measured and cut ropes to function properly. This then enables sheets to control and halyards to hoist sails efficiently. A general rule of thumb to calculating the length of halyards is to use the ‘vertical’ P / I measurements (height of the mast), while calculating the length of sheets then uses the ‘horizontal’ E / J, plus overall boat length.
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