The motor-driven hydrofoil attached to the bottom of a surfboard and powered by a battery in the surfboard is a fantastic idea that should be very successful both as a commercial product (if you can spare $12,000) and as a hobbyist project. Think jet skis that you can stand up on, but electric powered.
I predict motorized hydrofoil surfboards will take California and Hawaii by storm, but they may also be popular on Gulf of Mexico beaches. Someone here in Florida should investigate obtaining distributor rights from
Liftfoils, the original developer who is currently taking orders for delivery this fall and assembling boards in Puerto Rico (for now). It appears that pre-orders are threatening to exceed production capabilities, so these things may be in a situation similar to the Tesla automobile a few years ago. Definitely a hobbyist opportunity waiting here.
@billy bob surfer guy is going to need some expert design help to successfully build this one. The Chinese ducted fan motors, available in both brushless and brushed versions, appear to be up to the task, but I would not use a brushed motor for this application because, as
@Minder has pointed out, they are not reliable. The brushless versions with Hall sensors are the way to go, although the motor controller design is more complicated. Consider using
this one with a 48V LiPO battery. You could also use a lower voltage (24V, 12 V) battery pack with a boost converter to obtain 48V.
You really DO need a Bluetooth wireless, water-proof, hand-held remote control for the motor with a "dead man switch" motor turn-off capability when (not if) the rider falls off the board, or the remote is accidentally dropped in the water. This is a completely separate design consideration. Get some expert help because you probably will NOT be able to adapt an off-the-shelf commercially available product.
The battery and its charger need to be considered in depth. The prototype that Liftfoils is currently using is 2 kWhrs and requires about two and a half hours to re-charge from a 1200 watt charger. A "spare" battery (recommended for use at the beach where power is scarce or unavailable) reportedly costs $3000, so budget for two of them. Also budget for a gasoline or natural gas powered generator with 2 kw capability so you can recharge anywhere.
Finally, you need someone with expertise in laying up and building fiberglass surfboards. It's not difficult, but it does require planning and the use of noxious chemicals. Lots of surfers took to this as a hobby and a way to earn a little money, so you may want to see who is doing this sort of work in your area. Getting that motor mounted properly on the bottom of the supporting "keel" along with the hydrofoil lifting wing is of paramount importance. If possible you should build a parametric 3D model using appropriate software and analyze the stresses on all the parts involved, possibly using aluminum or stainless steel struts covered in fiberglass in appropriate places.
Sounds like a fun project if you have a few thousand bux to throw at it. Don't skimp on the electronics. Learn how to waterproof everything electrical. I would suggest using elastomer-sealed ("O"-rings) access covers, drawn down tight with
quarter-turn Dzus fasteners. Upload some pictures of your progress.