Roger Long wrote:
It's seldom realized but wind forces are not used in engineering
sailboat rigs.

Oh, I dunno, probably a lot of designers spend at least a
little bit of time on stuff like that.

... To design a rig properly, you have to know the
vessel's stability. You determine the maximum normal sailing angle
and the righting moment associated with it. That righting moment is
then divided by the sail area and the distance between the center of
effort and a point usually taken as half the draft. This give the
load on each square foot of sail which is then used to design the
spars and rigging.


Yes, but at that point, haven't the basic sailplan &
dimensions already been worked out?



For very conservative rigs, such as on a solo (non-racing) long
distance ocean cruisers, you might look at the righting moment at the
peak of the righting arm curve. No amount of wind can put more
pressure on the rig than at that point because the boat will simply
blow over farther to where there is less righting moment.


Sure. This is one reason why it's funny to hear people
talking about making their boats more seaworthy by upsizing
their shrouds. Unless they were undersized to start with,
and the chainplates etc etc also upgraded, this accomplishes
exactly nothing (expect the unnecessary expenditure of money).


You also sometimes want to look at loads under reduced canvas because
they will be much higher per unit area and may locally overstress
components that would be fine heeled to the same angle under the full
sail plan.


One way to figure loads on various hardware, deck fittings,
and the like, is to look at how much strain would be on a
tow line pulling the boat at speed. Then imagine letting the
tow line veer side to side, slacken for a moment and then
pop tight, etc etc. If this would break it, then it needs to
be beefier. In fact, on many points the load is higher
because the rig is not only pushing the hull at speed, but
the force on whatever given bit of rig/hardware is at a tangent.

And one point I like to keep in mind, no sailor ever
complained that his rig was too easy to handle because the
winches were so big

Fresh Breezes- Doug King