The Daytona hollow mast could be a promising solution for a big efoil company (Flite, Lift, …) but IMHO inappropriate for DiYers or small companies.
Here is a trade-off: the mast extension for ESC that can receive a compact ESC (@nickw1881, or a 120Acont 81x31x17mm MGM compro. The idea comes from the kitefoiling scene, costs 200 to 300€ in carbon (Groove, Ketos, …), 100+ usd in aluminium like Mantafoils or GoFoil. Here is the KETOS carbon one.
This efoil mast extension needs to be hollow, an ESC space must be easily waterproofed with a top and bottom joint, DiYed or CNCed from aluminium (like Mantafoils, GoFoil, …). The outside must be streamlined but the inside on the plate side can have a rectangular custom shape to match the ESC case.
This ESC mast extension could also be molded in aluminium around the mast airfoil section, see @Beninspain method using lost PLA (I am looking forward to watch you video casting a motor pod )
Shortest possible path between motor and ESC for cables and maximum simplicity in the board electric box.
The idea would be to encase the ESC in a small waterproof alu box :
1 - being either submerged in water (the mast extension being a small tank)
2 - or cooled with a forced flow from the pod = proven and shortest possible path as well
There is some sexiness to the solution but i am trying to resist .
Let’s look at it:
-3ft extra 7AWG wire is about 0.001 ohm
At 100A current it will create 10W of losses and most foiling is done at lower current. I’d think this is acceptable.
-Most cracked masts shown here destroy the mount so this puts esc unprotected. Also the mast area is always in the water, higher risk for leaks whereas the compartment even if it leaks a little during lifetime will not cause direct immersion problem for esc. (double enclosure in mast will be too bulky)
I see a benefit:
-if you have cut your compartment too small or using your favourite board without cutting, otherwise esc can easily be fitted cause surface is available and you don’t gain thickness by moving it to mast since you already need more height for the battery.