Propellers and Ducts


hj, i got a lower unit off a johnson 5hp outboard, planning to use the prop shaft and the seal plate piece, the prop is a little big 9.1/4" x 6.5 pitch, how did the. Solas Amita 3 Diameter 7 1/4" prop work out , thinking i might try that one on my ple60 5.1 gearbox with the sss360kv, would be great to hear how it worked out for you,


The problem with rim drive: patents patents patents.

Anyone thinking of putting that on a commercial efoil is in for a dozen Cease & Desist letters a week.


True. Have looked a little into it, found a few patents that are pretty old, so might be a small window to get around the remaining valid patents. Would be interesting to develop and build anyhow.


Actual energy potential contained in a cease and desist letter. Near zero, we have been told in the past to ignore them.

“Getting around” patents is a nice concept, but a patent holder has broad possibilities of threats, the only resolution of any conflict is legal action or mutual understanding. Even if it is seems glaringly apparent that there is no IP overlap. The slightest amount of overlap will open up a lawsuit.

A lawsuit, at the very end, after all the dust has settled, with a clear resolution of infringement, results in the court deciding on a penalty. The penalty is based on a value of the IP multiplied by the cost of the product being sold. With the possibility inthe US of triple multiple if deemed willful, countries like Japan, no triple multiple, just penalty.

The value of the IP is argued between the two parties before the court, based on what a reasonable licensing royalty. The patent holder says the value is 50%, the other party argues the values of the IP is a reasonable 2%. The court knows that a maximum licensing value for such IP might be 10%. The court settles on a value of 5%, for example. In the example of a rimless motor in a system, this value is based on the cost of the motor in the system. Total foil board cost sold by the “infringer” to his distributor $6000 retail value $10,000. Penalty is assessed on the price sold, not retail. Motor costs $400 * 5% = $20 * triple damage (worst case) = $60 * number of units sold. The other side will argue for legal fees, your side will argue against. Important here not to act wilfully, but to proceed through business actually looking to avoid infringing and act in the clear.

That, in the end, is the check that the patent holder gets for his hundreds of thousands spent.

Sucks to be a patent holder for a small idea.

The amount of cases that ever reach this stage is probably less than 1%, everyone realizes (exception Samsung v. Apple) that there is no benefit in continuing the legal fight past some point of financial pain.

Bottom line, make your good ideas, innovate, and don’t be intimidated. Incorporate. :slight_smile:


So be first with the innovation, have plan and means to execute, get ahead of pack, make sales while sun shines, while everyone else copies you.


Has anyone thought about using a mesh cowl rather than a duct?

I.e. a robust mesh for safety to prevent fingers and general mincing, but avoiding the limitations of ducting and also the lower maneuverability of solid duct when turning or rising/falling?


Hi Aaron
would you mind re-sharing the Dropbox link, it expired. I’m not commercially interested, I’m planning to build my own e-foil and still analyzing and evaluating different designs. 3d assemblies are a great way to understand how other people built something, before actually building it. Helps to avoid mistakes.


Looks like you got a nice prop! :smile:
I just thought it would be great to scale this one down so it can be used with @pacificmeister 's build so here it is
The second one is the same but I just kept the 9.6mm sided square hole

the scaled prop on the left, the original @tunnelvision on the right


Oh I forgot, with this one the duct needs to be a bit longer but I couldn’t modify it because my solidworks version won’t open the duct file correctly
But maybe it’d be better to scale the duct up to @tunnelvision’s prop size


Hi Daniel,

Will do. What your email address? Do you use onshape?



Hi Aaron

Just been printing out your prop and other parts in pla for testing but will be getting some apolloX soon. Just wondering what bearings, seals etc you use with your setup and where to buy them? I’ll probably copy your board to mast connections too… Where did you get those?



Hi mate. What’s your email address and I’ll give you access to all my CAD via onshape. Using skateboard bearings 608 is the spec and seals of the same size that can be found easily at any bearing shop.





That design looks great. I have recently gained interest in prop/hydrofoil design as I am taking a fluid mechanics lab for college. Could I also see your CAD files? I am interested in learning more about all of this stuff. My email is



aus Zeitmangel verkaufe ich meinen Momentum M90 Antrieb er ist getriebelos und sehr kraftvoll denke es würde sehr gut funktionieren dabei ist eine Motorhalterung aus Schwarzem POM auf Wunsch auch ein Alpine Foil mit dem XLP2 Flügel und des weiteren habe ich noch ein Kiteraceboard perfekt um zu basteln.
bei Interesse

mehr Informationen unter


ja ich will das Projekt verkaufen wer also interesse hat kann sich melden


I got a question: I made my propeller from a normal outboard prop which i cut down on a lathe to fit to the duct.
Shall i round these edges or shall i keep them sharp?


Never Ever round any edges on the forward part of a prop, keep these sharp


Not sure if i understand you correct, what is the forward part of a prop? Maybe someone else can help me?


The forward part is the one that would cut your finger if you stick it into the prop. You didn’t change the forward edge though. The place you machined and at which you are pointing the arrow is the blade tip.