Tension measure of split aft stay

[John Berlin]

I have always used a Loos tension gauge to measure the amount of tension on my rigging. Now I have purchased a Catalina 310 with a split aft stay at the lower end of the aft stay. When the lower part of the aft stay is shared with two stays how does one use the Loos instrument which uses a stay to measure the tension placed on it? John Berlin, Barling1@benzie.com

 

[Justin - O'day Owners' Web]

Above the split

The overall tension in the backstay sytems is determined by using the Loos gauge on the backstay above the split. You need to get high enough to ensure that the the rigid swage fittings at the union do not influence the reading.If you have a block at the lower terminus of the aftstay through which a wire runs rigidly attached at one end and controlable at the other, you can take the tension on one leg of that run and double it. If you have two fixed lengths below the union you need to do it above the union.Justin - O'day Owners' Web

 

[Derek Rowell]

A little mechanical engineering analysis....

If you do what we engineers call a "force balance" on the back stay, and you assume that each of the split stays supports half of the tension then you will find that the tension T is T = 2 x Tlower x cos(theta)where Tlower is the tension in one of the split stays (as measured by the Loos guage), and theta is HALF the angle between the two lower split stays (cos() is the cosine of the angle)If for some reason the tension is not the same in each, you can simply add the components: T = (T1 + T2) x cos(theta)where T1 and T2 are your two measurements.You can compute the required cosine very easily: cos(theta) = L1/L2where L1 is the measured distance of the "missing" piece of the backstay, ie the distance from the split point to the transom, and L2 is the length of one of the split stays. (Note: L1 must be less than L2)Hope this helps,Derekdrowell@mit.edu