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Re: Forestay to long, back stay to short!!!

Posted: Sun Jul 26, 2020 7:21 pm
by 1st Sail
Glad you have this sorted out.
FYI Following is my mast rake calculator for any length mast or plumb line. I just installed a new Schaefer CF500 furler and set my M mast to 1° rake aft. In light winds I have a very slight weather helm which BWY confirmed as proper setup for the M. With the boat on the trailer I used a laser level on the boot stripe and the main halyard as my plumb line. The after sun set I lasered the mast as a second reference point.

Here is a rake calculator in degrees of rake and length of the plumb distance from vertical. ... olygon.php

Choose a Regular Polygon (n>14) Other
Enter Polygon n = 360 360=1°, 180=2°, 120=3°, 90=4°, 72=5° etc.
Choose a Calculation Find a, R, A, P, | Given in radius r
R= 360 (length of mast in inches, 30’ x 12”=360)
Let pi = 3.1415926535898
Units ‘in’
Significant Figures 4

Side length a=6.283 for 1°
Side length a=12.57 for 2°

Helps to have a structural engineer for a daughter.


Re: Forestay to long, back stay to short!!!

Posted: Mon Jul 27, 2020 6:16 pm
by Jimmyt
Excellent Dave! And congrats on the Structural Engineer Daughter. I got a Registered Dietician, an Industrial Enginner, and a School Teacher. 3 successful launches. :D with two Engineer parents, it's a wonder all three of mine didn't wind up in therapy. :D

You can also divide the plumb bob offset by the length of the line and take the inverse tangent... if your phone calculator has trig functions (don't they all?). This will give you the angle from your plumb bob measurement. If you want a specific angle, take the tangent of the angle and multiply by the length of the plumb line in inches. This will give you the desired plumb bob offset distance for that angle. Same cat; different skinner.