Full sails designed for up to what wind speed?

[svMira]

I'm building a spread sheet to take a look at wind loads on sails. Just a simple wind speed x sail area to get force. I'm trying to compare loads on different reefing/sail combinations. I was wondering what wind speed is presumed when a designer adds a sail rig to cruising boat? Figured that should give me a safe pounds per square foot max load number to use for downsizing higher wind speed sail plans. But, I don't know what that base speed that would be. Anyone have ideas?

[atomvoyager]

Maybe someone else has an idea but I can't imagine what that number would be. Whatever number a yacht designer came up with for sizing sails and rig, they'd add a substantial amount for inertia and shock loads, boat size, specs and other factors. And you can carry different amounts of sail at different wind angles. Maybe you could approach it by starting with an approximation that most moderate displacement cruising boats can carry full sail in up to say 15 knots of wind and then calculate back from that based on those boats published sail areas. But there is a wide variation among boats due to all kinds of factors. Not sure how it might play into your calculation but for example, as you reef down at higher wind speeds the hull, deckhouse, spars and rigging add a substantial percentage of the force of wind the boat reacts to.

[svMira]

I'm just trying to work out comparative safe loads. Figure if I work with that number as a reference, the rig will already be built around the breaking load, so I can ignore trying to work that out. I wanted to see the force numbers in the rig as the wind builds and then see how small a heavy weather sail set I needed to get down to those same 'regular' loads.

I totally agree with you about the deck and hull counting more at higher speeds. It almost seems silly to put up heavy weather/storm sails when there is more lateral area in your hull/deck than in the sails you are raising. But I guess they are in the right place, the right shape and not ducking under water half the time.

The Wanderer has 424 sq.ft. of sail as designed. At 15 knots, that's 410lbs pressure. Somehow that number seemed low to me. But really it doesn't take that much to move a boat. And a gust of 20 knots bumps that up to 729 lbs. It isn't hard to double the wind pressure in a gust. Ballast is 3800lbs 3' down. 729 lbs pressure 15 feet up pushing the boat over sounds like about time to reef to reduce that load. If I look at it that way, it seems to make more sense.

So if 410 lbs is normal sailing pressure, then if I want to sail (somewhat upright <grin>) in 30 knots of wind, I have to be down to a sail area of 126 sq.ft or so, 489 lbs pressure. The sails are smaller, so a gust up to 35 only bumps me to 665 lbs.