Is there such a thing

used to know where to get them, about $25 from memory

Not sure that hemp fibres are as good as Carbon

You could have raked "weed" foils
You could have a raked "weed" mast
Unfortunately that would all come unglued by the fantastic weed catcher which is the foil fuselage.

Surprisingly weed impacting foiling isn't the issue I thought it would be

The weed at my local beach, South Fremantle, is usually bad enough that I need a weed fin on my slalom board.
When foiIing, I drag weed at times which drops the nose of the board - but I'm still flying. Only becomes a pain when the wind is really marginal.
The weed falls off the foil easily when tacking.

And the big bonus of foiling this notoriously choppy spot is the ocean feels flat - no need to sail in ankle-deep water

I think a weed foil might be razor blades on the front of all leading surfaces. Sometimes I feel like I'm a combine removing all the weeds from the lake when sailing. Oh well, at least next time there will be less.