Water levels have dropped in some inland lakes and using a shorter mast is becoming a reality. Who knows what the shortest mast size is to generate lift ?

Mast height is more about giving yourself margin of error to keep the board off the water and the foil under the water. More mast means less breaching or touching down esp if there is swell.

Most people like at least 85cm but some can get away with 60-70 cm if the water is very flat

55cm is doable. Great for beach starts. You have to be more active trimming as you don't have as much "clearance" to play with.

I've done 65 and it's a task. The water has to be pretty flat and your ride height pretty wired. Like you, I was restricted by depth so didn't have much of a choice. If you need to go much shorter than that, probably much easier mentally to just use a fin. If it's that shallow, you'll worry about hitting bottom and wrecking a wing or the nose of your board constantly. fwiw, my usual rides are 95s.

They're all good ideas thanks. My normal mast is 85 and my buddy's mast is 70 - he hit the bottom and luckily only had some scratches. The lake is really flat when foiling at 15kts, I like the 55cm suggestion the most or going out in a boat and checking the depth.

Well a solid carbon foil mast, wing, and fuselage helps when you do hit bottom, realize AFS masts are too long for you with shortest at 85 cm, but the can hit all kinds of things at full speed, sandbars, bay bottom, manatees, and not show any damage.

The funny thing about mast lengths is that the effect is non-linear. If it were linear, a 90 cm mast should be 50% better than a 60 cm mast. But the difference feels a lot bigger, at least if you have some chop.

I have foiled on 45 cm masts, but that means the board touches the water a lot if there's any chop, and you've got to be really careful with backfoot pressure to the side. 60 cm masts are a lot easier, and 70 cm masts are perfectly fine on flat water, and doable in 50 cm chop. At our spot, 90 cm masts work only near high tide, so most foilers use 70 cm masts most of the time.

On the upside, shorter masts make it easy to keep going after overfoiling, although that may vary a bit depending on which board you're using.

I learnt on the Slingshot Flight system which goes from short to taller masts 15" (38cm), 24" (61cm) and 30" (76cm). Although I have a 90cm I've kept using the 76cm as I can transport the foil assembled.

In light winds inland there is not much chop height so even the 61 cm slingshot is easy enough. Just adjust so you can keep your time on the water.