Has anyone measured how much faster they go with the same foil/board and wind speed using different size sails? I am trying smaller sails in conditions that I would use a larger sail, so a 5.8 instead of a 7.2/8.0. I find with correct technique I can foil with the 5.8 but feel like I am going a little slower than with a larger sail. Am I imagining the speed difference or is it real?
Thanks

I find it's not sail size, but also sail power, and how it's tuned. Pumping once already up has a bearing, as does what angles you go to get up to speed.

Select to expand quote

LeeD said..
I find it's not sail size, but also sail power, and how it's tuned. Pumping once already up has a bearing, as does what angles you go to get up to speed.

Thanks LeeD

Keep tracking that Sandman1221.
Note that Goyard's recent victories were using a sail 1.5-2 meters smaller than his finned competitors.
Any more sail than what is needed is drag and it slows you down.
I had the light bulb moment with this years ago while racing ice boats. I raced the DN which is a tightly conrolled class but allows some development. There is a max sail size but no min. On clean fast ice I was getting pased by smaller flatter sails. My personal best speed,50.3 knots was set with a small sail. If the class alowed it there would be smaller masts to accompany the smaller sails. We have that option with our windsurfing rigs.
As foil design progresses and hydro drag goes down so too will optimum sail size.

I haven't measured but smaller sails tend to go faster, but the other big dimension is rig tension. I had a 5.2 Sailworks Revo wave sail that I could foil with in 15-20knots on a soft mast and 20-25 knots on a stiff mast. It was quite fast on top end with the stiff mast as I assume that the stable airflow over a sail that does not distort is more aerodynamic.

I find the same with Ezzy Hydras. As I increase sail tension with all other equipment the same, top end speed increases.

utcminufour and tswei99, interesting information, thanks!

So how do you know what sail size is as big as needed for the wind with a given foil/wing, other than logging gps speed? I know I used an online sail size calculator for windsurfing, any for foiling?

Windsurf sail size minus 2m

I find (as above) smaller sails are faster. In the cross over of wind strengths they'll function in. But that's only one piece of the puzzle. My 8m (talking race foil sails) starts to function properly at around 12 knots. My 9.5m also functions at 12 knots. my 8m will be faster upwind than the 9.5 will, but I won't be able to point as far upwind (or downwind) as with the 9.5, and when the wind lulls to 8 knots it'll stall. The 9.5 won't.

Wing sizes are simple (for me at least.) my small wing won't be powered properly below 15knots of wind, so that's when I make the change. By that stage I'm on the 8m regardless. Of course, that's for a course racing scenario. Going purely for speed, where you're not going upwind or chasing vmg, I'd just go for the smallest sail that would stay powered.

Select to expand quote

Sandman1221 said..
So how do you know what sail size is as big as needed for the wind with a given foil/wing, other than logging gps speed? I know I used an online sail size calculator for windsurfing, any for foiling?

For me it's just something that comes from sailing them in different wind strengths. Trial and error (lots of error). Then reviewing what happened on the wind graph afterwards.

Select to expand quote

Subsonic said..



For me it's just something that comes from sailing them in different wind strengths. Trial and error (lots of error). Then reviewing what happened on the wind graph afterwards.

Yes

A lot of time on 9.0 and racefoil made it easier to just deal with overpowered situations when using freeride foil kit (slingshot). I worry more at the high end of getting into survival mode but it's not as common here. I know that if it gets a bit lit up on my 6.6 and i76 that I can safely make it back, just point deeper downwind and upwind to deal with overpower with apparent wind or with using the foil lift to push upwind harder. Same with being massively overpowered on a fin but the angles are less (and my experience is now less as well). But the i76 doesn't point as high as the race foil, and it's very noticeable in comparison.

After more TOW I know that if it's not happening with a 6.6 and vigorous pumping on the i76, it likely isn't happening with a larger sail. I don't have a board appropriate for the very aft lift of my i99 so I don't bother now (saving it for a wing maybe). But the 5.0, 5.8, and 6.6 cover me for 90% of the time I want to use freeride gear on a foil.

When I first started foiling I couldn't figure out how to deal with overpower and would limp home by flagging the sail and shlogging back. Getting over that fear and getting deeper angles made a lot of difference, but it wasn't "comfortable".

okay, lots of good advice, really appreciate it everyone! I thought I had it figured out for my AFS W95 foil and Aerotech Freespeed sails, but then tried my 5.8 sail with 770 wing in 12ish knots (because forecast was for wind to pickup, but it did not) and was flying fine, but normally I would of used the 1080 wing and 7.2 sail in those conditions, then wind dropped to 10-11ish so switched to 1080 wing and kept 5.8 sail and kept on flying, normally I would have been on the 7.2 sail and 1080 wing. I am certainly more experienced now, but did not expect the sail and wing range to drop at all at this point. Guess it is time to sell my 9.0 sail, 490 mast and 200-260 boom!