Oh yes I didn’t see the ratio, I would imagine its the other way round as in a reduction.
You could mount the motor drive shaft pole touching the trailing edge of a standard mast then 3d print a hydrodynamic surround to go around both the mast and pole, it would be chunky and a bit draggy but I think it will work OK.
Yes, it should have a long chord (30+cm) given the thickness but it will work.
https://www.aliexpress.com/item/33035622470.html?spm=a2g0o.productlist.main.109.5f90503edoi02A&algo_pvid=b509dd0e-faf3-4fcb-8be4-1ef7440c3bb0&algo_exp_id=b509dd0e-faf3-4fcb-8be4-1ef7440c3bb0-54&pdp_npi=3%40dis!HRK!2223.11!1289.37!!!!!%40211bf14716856935623011896d082f!12000018236383253!sea!HR!119950568&curPageLogUid=pGf6B6Lj4xMa
two of this little babyes could make good build. if you can make big enough compartment maby tay will fit inside board.
maby even one would be enough if you gear it 1:3.
Those gasoline 2-stroke engine for RC boats are water cooled (ggod thing) but are only 29cc. For extra power and torque, there is also this water cooled 43cc:
https://www.aliexpress.us/item/3256805109769595.html
Im really interested in a Gas(petrol) powered Foil board. Its probably a tenth of the price of an E foil, better for the environment and power grid, and the noise can be kept to a reasonable level. The picture of the weed wacker setup above looks great. Any idea what brand or size of motor is in this picture ? And does anyone know of a working Gas powered Foil board ?