Discussion on this topic is not recent as far as I can tell. With advancements in technique and equipment, I'd be interested in your thoughts on the following with these scenarios.
1/
8-9 knots
150 ltr foil board 90 wide
60 Kgs
2/
8-9 knots
150 ltr foil board 90 wide
80 Kgs
3/
8-9 knots
150 ltr foil board 90 wide
100 Kgs

What size cambered race sail would each of these sailors need to foil. Intermediate skills, weekend warrior?

I can only speak of scenario 1 based on personal experience. With a 900/1000 cm2 race foil, easily off the water with 7.7 freerace or 8.0 full race. In colder, denser winter air, I can probably do that with a 6.7. This assumes your pumping game is good, though.

I'm 80 kg, and with this wind I use a 8.0 Loftsails Skyblade with 725 front wing and 95 fuselage. My limit is 7-8 knots with this configuration.

That is pretty good work XavierFerrer - congrats. We have a very diverse range of sailors where I sail - I am interested in the limitations for the different weights and at what point a larger sail does not help. eg if a 100kg sailor was on the same gear with the same conditions would a 10-meter sail work or does diminishing returns kick in earlier?

A10m is nice but you can't beat the 11m if light wind is your goal. You actually have something to lean into as you pump.

I'm 100kg on a 91cm, 163 liter board, intermediate foiler. I can't yet foil up in 8 no matter what but can stay on foil easily in an 8kt lull. I can pump up in 9 with an 8.5 (pictured in my avatar). The 8.5 is a very light Foiling-specific sail. I don't get up on foil any earlier on a very light 10.0 HSM although it will plane earlier on a fin than my 8.6.

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DarrylG said..
A10m is nice but you can't beat the 11m if light wind is your goal. You actually have something to lean into as you pump.

This guy here knows...

Am 68kg and 1m86 tall
Future fly 145 foilboard + starboard carbon race foil.
1000 / 115 black fuselage /255

7,7 Ga sails cosmic 2cam freerace

Pump up in 7kn/8kn no problem at all and keep flying in less.

How is everyone measuring the windspeed? At what height? With what equipment and where is the anemometer located relative to the sailing area. Is there any consistency between contributors on this ?

Good question. We all talk about wind speed. Anemometers at anywhere from 1 meter to 20 meters high, located everywhere. In the middle of a body of water, edges, even behind buildings or trees in some cases. For that matter, how many anemometers are even calibrated?

Windsurfers seem to have figured out, over years of history and discussion and debate, about how much wind translates to how much whitecapping, and about how much wind translates to how much pull on a given sail size and type and cut and draft.

See? It's all VERY simple, huh? Very empirical and very subjective. That's about as good as we can get it, I think.

I know what 15 mph wind looks like and feels like. There ya go. Scientific.

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sheddweller said..
How is everyone measuring the windspeed? At what height? With what equipment and where is the anemometer located relative to the sailing area. Is there any consistency between contributors on this ?

Very important question! Even with a given anometer at a given spot, wind direction comes into play. I can foil intermittently with a small sail when the average wind readings are 5 knots .. in offshore wind at our local . At the same time, the wind meter that's mounted on top of the bath house 200 meters away may show gusts of 15 or 25 knots, depending on the exact wind direction.

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segler said..
Windsurfers seem to have figured out, over years of history and discussion and debate, about how much wind translates to how much whitecapping, and about how much wind translates to how much pull on a given sail size and type and cut and draft.

Many of the guys who "have figured it out" end up rigging, going out, and then coming back in to get something larger or smaller. A few are well known to spend more time rigging up and down than actually sailing..

Yeah a lot of my knowledge about windspeed, short of an anemometer on the shore, is site and direction specific. One wind meter reads about 5kts above reality on the water, but the trend and direction is indicative. Also, some spots are so turbulent in some directions that you can't even stay planing long without a lot of effort. Foiling makes it easier but timing the pump for a good gust in confused swells makes it a challenge.

I've recently got new batteries for my anemometer and what I was thinking 10kts was lower than that. At least the water state usually tells me about what to expect, unless it gets to about 6.0 fin weather and below. Then I just rig and find out.

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California said..
Am 68kg and 1m86 tall
Future fly 145 foilboard + starboard carbon race foil.
1000 / 115 black fuselage /255

7,7 Ga sails cosmic 2cam freerace

Pump up in 7kn/8kn no problem at all and keep flying in less.

I'm running a similar setup.
2022 Starboard freeride foil 150
1000/900/800/ 115 black fuselage/ 255 shimmed to -2 degs
8m np v8 flight

82 kg, 1.80 m tall

Any larger sail size and you really need to switch to a 95 wide board... iqfoil or equivalent

For me, i look at the water and if i can see enough wind to feather the surface slightly in the gusts, i can get flying on the 9m HGO with my IQ foil set up. That usually equates to between 6-8 knots on the anemometer readings at my local spot on seabreeze.

Written above: "Many of the guys who "have figured it out" end up rigging, going out, and then coming back in to get something larger or smaller. A few are well known to spend more time rigging up and down than actually sailing.."

Those few are very few, none at my local sites. We check the anemometer report online (if there is one), check the appearance of the water, ask around (if others have been out), rig, and sail. If we guessed wrong, too bad. We make it work.

The only time we re-rig is if the afternoon thermal kicks in, and the wind goes from 15 kts to 25 kts.

60kg when fat. In single digit winds I use my "large" sail. 5.5M but a huge wing. The SS HG84. 5kts requires a bit of effort (proper pumping)to get up foiling. ~7kts is realistically needed to get easily on the foil.

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OldGuy3 said..
60kg when fat. In single digit winds I use my "large" sail. 5.5M but a huge wing. The SS HG84. 5kts requires a bit of effort (proper pumping)to get up foiling. ~7kts is realistically needed to get easily on the foil.

Similar to you, new 5.1 m2 Goya cypher is my largest