Direct Drive Outrunner Prop - Not an eFoil, but

I’m working on a non-eFoil project, but I’ve drawn a lot of inspiration from the direct drive threads on this board so I thought I’d share some pictures in case others find it interesting and/or useful.

I wanted a kaplan style propeller for use with an APS outrunner motor and, of course, there is no such thing available anywhere. So I made one. It’s designed to allow as much cooling water to flow through it as possible, with matching openings at the back of the prop to the ones on the rotor housing. The rotor slips inside with about 0.001 to spare and four M3 screws retain the prop to the mounting holes on the rotor.

It’s 7.5" in diameter and machined from 6061. The witness marks at the roots of the blades aren’t TIG welds - they’re from the contour machining operations.

Came out pretty well! Though I have a long way to go before I can test it…



Wow, that is what many of us need!

that’s huge… what are you propelling with that??? :slight_smile:

The diameter is large, but the pitch is shallow.

At the blade tips, ΔX from the leading edge to the trailing edge is just over 1/2" which, together with the blade width and a little math, leads to a total pitch of only 4.7". With a 90kv motor and an 8s battery, the unloaded theoretical max forward velocity at full charge is just under 11mph.

The Kaplan prop / Kort Nozzle design is intended as a high thrust low speed configuration, which is what I’m driving for. Think “tug boat” (which is actually the prototypical application for a Kaplan/Kort combo.

I’m targeting a speed in the 3-4MPH range with a heavy load and 60-70% throttle.

I built this around the 50mm outrunner from APS, which should be plenty big for this application.