Hi
As in many other cases I've seen different advices on the net for mast foil length in open sea with swell.
My coleagues tell me that they need 95 cm mast to fly over the swell at the sea not to dip in the valleys. However Casey at WWF web site tells he uses 29'5" mast (75 cm) to surf the swell.

As beginner I prefer 80 cm because it lets me bechstart and not walking for a Km in shallow shores.

Thanks.

Racers here mostly use 95 to 110.
Shorter has better wave riding feel.

I've used 85-110. I kind of think this depends on the foil and how fast you want to go.
Personally I'm into foiling to feel the swell and ride around it, 85 is fine.

Casey at WWF is on one of the great lakes upper midwest usa he does make it look easy on that 75 cm but he is also strapless.90-95cm is about as long as you can buy an aluminum mast any longer you have to go carbon. Me I like at least 90 makes for less mistakes and it's kind of fun when you are way up on the edge

Mast length is always a compromise.
Longer IS easier once clear of the shore break. A longer mast can be faster but is slower unless you are skilled and can ride it high.
One of my spots is an ocean beach break and my 90cm mast is usually a disadvantage. Often my mates on 75cm kite foils are smashing the lip right next to me while I am still walking out to get deeper water. I rarely get to ride breaking waves because it is to shallow. When the surf starts to get bigger the shallower foils help you get free of the impact zone. In other words you CAN get out and it is easier to do so because you can sail sooner. Smaller masts and shorter fuses are lighter and that can make carrying the gear to and through the surf easier. I am planning on getting a 75cm flanged mast for surf sailing and or low tide shallow areas. I love ripping on auto pilot when the lump is less than my mast height. I also love contouring the waves, always staying the same height off the water as the waves slope. It fells so fluid, surfy and engaging! There is no wrong answer, it depends!