Effect of foil mast length on planing, leverage, etc.

d0uglass

I got a foil as an early 40th birthday present. It's a 2019 Slingshot Fwind. I intend to use it on my 2004-ish Exocet formula board. (I've reinforced the deck over the finbox to hopefully avoid the finbox ripping out prematurely). The package came with a 61 cm mast, but I also bought a 90 cm mast for it.

What exactly does a longer mast help with? Just with avoiding breaching the foil or touching down inadvertently in choppy water? Or does it also help with early planing and leverage for standing in an outboard position, like a long conventional fin on a formula board does?

I'll probably try the foil for the first time tomorrow with the 61 cm mast.

kmf · Joined: 02 Apr 2001 Posts: 503

Jim, was checking out your sailsize calculator and I can’t enter my weight in to the excell box. I am using an I-pad. Any reason for this?

Kmf

boardsurfr · Joined: 23 Aug 2001 Posts: 1266

Good question, let me know what you find out Smile

. I think shorter masts are good for the first steps, since you can start and sail in shallower water, and the crashes when breaching (or suddenly going down) are not as dramatic. Once you get the hang of it, the longer masts give you more room for lateral movement. If you watch videos, you can see even good guys using most of the length of the mast in a run - sometimes just above the water, sometimes close to breaching.

If you start racing on foils, other factors may come into play. Good racers often have everything tilted windwards, and a longer mast works better for that. I remember hearing that some guys even go to narrower boards to allow higher tilt angles without having to worry about the windward rail touching. Not sure how much there is too this, though.

DanWeiss · Joined: 24 Jun 2008 Posts: 2296 Location: Connecticut, USA

A longer mast allows greater leverage over the foil since it increases the distance between the wings and your feet. A longer mast also allows the board to fly clear of larger chop than it could do with a shorter mast.

That's all I know.

dcharlton · Joined: 24 Apr 2002 Posts: 414

Longer masts is actually easier once you get over the fear of heights. I don't feel I lose any control with the long masts and I'm not constantly breaching in steep chop.

wsatl · Joined: 30 Sep 2014 Posts: 66

d0uglass · Posted: Wed Mar 27, 2019 11:28 am Post subject:

Maiden voyage went pretty well. Did a lot of flying and crashes were not bad enough to break equipment or cause injury. Plenty of power to fly with a 5.5 sail in 15-17 kts wind. Felt overpowered and had to sail sheeted out a lot, actually, and struggled to keep from overfoiling. Did a lot of inadvertent porpoising up and down from overfoiling to touching down. Choppy, wavy water added to challenge of not overfoiling or touching down. I had to keep my back foot quite far forward and on the centerline of the board to keep the nose down and not round upwind. I put the back foot in the chicken strap sometimes but it seemed like it would be impossible to get the back foot in the outboard footstrap without instantly overfoiling and rounding upwind. I have the wing in the most extreme forward position now and I think I might move it back to the middle position to reduce the amount of front foot pressure I need to keep the nose down. I'm also eager to try it in lighter wind with smoother water.

coachg · Joined: 10 Sep 2000 Posts: 3550

A 5.5 is a way bigger sail then I would use in 15-17 knts with a foil. Try a smaller sail in that wind to see if you can gain more control. At 170 lbs I would use a 4.2 sail in that wind.

Coachg

NOVAAN · Joined: 28 Sep 1994 Posts: 1549

At 165lbs and a mid size wing I would be on a 4.7. That said, when you get more time on the water, Your lite wind range and top end range will increase for a given sail size. I like to rig for the gusts because it takes so little sail power to keep flying once your up.. have fun in your quest to foil...Keep us posted

grantmac017 · Joined: 04 Aug 2016 Posts: 946

Possibly shift the mast base a bit forward. I find larger sails need it back, smaller forward.
Your back for is forward and inboard because of how far out a formula board puts the front one. A set of inboard mounts could help. With sails under 5m I can run front straps only 15cm apart if I wanted. When I was using a formula board I just placed my front foot on the deck with the outside against the inboard part of the strap. I'm not convinced foiling really needs straps unless jumping or controlling big sails for max VMG.