How to find angle for swept back spreaders

[kevinmal]

Existing rig has in line spreaders and runner back stays . I want to change this setup to swept back spreaders and do away with runners . The existing bulkhead has some rot and needs to be replaced . I can only move the bulkhead aft 25 cm because of engine mounting in the way . But how do I calculate the angle and length of the spreaders . Any help is most appriciated .

Thanks Kevin

[Buc]

If the runners are needed to keep the rig up, 25 cm won't allow enough sweep to eliminate them. You'll need at least 15 degrees and 20 would be better.