Electric Thruster Fin for Paddle Board (SUP)

Summary:

Have you ever thought of attaching a Motor to your inflatable Stand Up Paddle Board? I have but I don’t like the ones you can buy, so I made this:

This Stand Up Paddle Fin is designed for the Apisqueen U92 underwater thruster that you can get here:
12-24V U92 Underwater Thruster,10.7kg/11.8kg Thrust Brushless Motor For Boats | eBay

[Edit, 2026-02-12]
There is a new Version of the Apisqueen U92 Thruster. Motor and Impeller are different but the outer case is sthe same. Should also fit the fin:
 ApisQueen 24V U92 Pro Underwater Thruster, 23.6Lbs Thrust For Fishing Boats | eBay

The Thruster is rated for 24V but it works fine on 18V powertool batteries.

The fin is compatible with boards that have a slide-in fin. It prevents the entire fin from tipping forwards due to the propulsive force with a forward extension. This extension directs the resulting torque to the underside of the board. This prevents the fin slot from being overloaded. A locking pin is included in the files, but I recommend making an aluminum pin instead of the 3D printed one for obvious reasons.

Other parts used (Links):

• RC Wattmeter (Energy Monitor)

• Servo Tester

Changelog:

[Edit, 2026-02-12]
Added Link for new Version of the Apisqueen U92 Thruster.

[Edit, 2025-07-16]
Added Bosch Professional 18V Battery Adaptor. I designed this several years ago - added it in case someone wants to use Bosch Batteries.

[Edit, 2025-07-16]
I am working on a third version that will have a Servo controlled Rudder behind the thruster. Will upload as soon as the prototype works.

[Edit, 2025-07-16]
I have added the Metabo-Battery adaptor I designed for this project. Caution: Be really careful when working with power tool batteries. They are very powerful - short circuit or misuse can lead to serious demage or Injurie. 

[Edit, 2025-07-15]
Will add my 3D-Printed Metabo-Battery Adaptor in the next days. If you want to use Tool-Batteries, there is a lot of Adaptors for various Battery brands on Printables.

[Edit, 2025-07-11]
Added a smaller Version of the Fin. It has less directional stability when paddling but it also has less drag. Of course, printig is also faster.

Printing:

The Fin is divided into four sections so that you can print it with a Prusa MK3/4 or Core One. 
I highly recommend printing it with 4-6 perimeters for extra rigidity.

I printed it in ASA with the following settings:

• 0.3mm Layer Height

• 6 Perimeters

• Normal infill

• Brim enabled

Assembling:

There's four 8mm holes that go through all of the parts. I recommend inserting 8mm carbon rods or pipes to align the parts while glueing. Also, those rods will greatly improve stiffness of the fin.

The smaller version of the Fin has one 6mm hole for a 6mm carbon rod, as an 8mm rod would be too wide.

I used 30min Epoxy to glue everything together.

Electronics:

Batteries: As you can see, I use 18V Powertool Batteries, they are plenty powerful and I have several of them anyway. I use three 10Ah Metabo Batteries. This leads to a run time of around 1h at full steam ahead or 2-3h at medium power. 
The current at 20V and full Power hovers at around 25A. The speed is around 7km/h. Use 24-28V (6-7S Li-Ion) if you want more speed. 

You will find the Metabo 18V and a Bosch 18V battery adaptor in the files. You will find adaptors for other Powertool brands here on printables.

ESC: What you also need is an ESC, electronic speed controller. You can basically use any cheap RC-ESC as long as it can handle a constant current of around 30A without overheating. I recommend using at least an 80Amp ESC. Of course, you can also use a water cooled RC boat ESC but in my case, a cheap airplane ESC works just fine.
You may want to use a small fan to cool the ESC as there is no airflow otherwise.

Caution: Make sure that the Low Voltage Cutoff Option of your ESC is activated. Otherwise, you can fully drain your batteries and destroy them.

Controller: I control the ESC via Servo-Tester and potentiometer. Of course, you can also get one of those fancy, wireless and waterproof surfboard controllers but I am too cheap for this option, haha.

Power Monitor: I used one of those cheap RC-Wattmeters. Works nicely - you can see power consumption, voltage, current and most importantly, used charge.