Neutral Axis

The neutral axis of a section is it geometric centre of area. If plane sections remain plane and a bunch of other engineering stuff, then when you bend a section along its principal axes then there is no strain on the neutral axis that is to say it is between the region of compression on one side and the region of tension on the other side. For mast sections it is commonly confused with the centreline. If a mast was a perfect circle or ellipse the neutral axis would be the centreline too. However for most mast sections they represent an egg which has been booted up the backside or if you prefer an inflated bullet. In any case the net result is that the neutral axis is some 55% to 60% aft along the section. The question arises, should the spreader rake and chainplates be set from the neutral axis or the centreline? There actually isn't much difference. You could argue that by putting chainplates and stays on the centreline it will induce mast inversion because you are compressing the mast on the forward face. However, the mast will probably still bend the same way and the so-called inversion will actually stiffen the mast up. Further some people get really lost because with stiffening in the mast the neutral axis can move in every mast panel. So at the end of the day use the mast centreline is our advice. Thus V1 chainplate for an inline rig is halfway between front face and aft face of the mast when you layout the deck plan.