Okay - I have thought about this and drawn some diagrams.

Lets look at diagram 1:

This is the classical formula. The force on the suspension is as everybody says. No argument

Now lets add a structural ridgeline:

Now in this case the force F2 is, as before, some force divided by the sine of the angle alpha. The difference is that the force being divided is no longer the weight of the occupant. The force of the ridgeline has entered the scene and altered the angle from beta to alpha. The force f-one in the diagram is now given by the usual formula - no argument. The force f-2 is given by the same formula using the angler beta. But the force used to compute the force F-2 is no longer the weight of the occupant.

The wife is ringing the dinner bell and getting anxious - time to go.

So hitchcraft and BB are right the force on the suspension rope is given by:

D/(2* sin(alpha))

Then I guess where we disagree is that hitchcraft seems to have wanted to say that D is equal to the weight of the occupant and I disagree. Don't have time right now to derive what D is though. The wife is calling for dinner.

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