Electric Surfboard

[Cativo]

I am building a DIY electric surfboard and have found a few threads on the subject, but I first want to understand what the best approach is to the powertrain. I would like to achieve 10-15mph hauling a weight of about 150lbs. For obvious safety reasons, I need to use a jet thruster and not an open propeller.

In this application (slow speed, large weight), I am assuming I need higher torque, larger prop, and lower RPM to maximize low speed thrust? Some other people are using smaller dual motors, but I want to keep it a single powertrain.

Since this is just experimental, I?m trying to keep it cheep so a Jet 52 MHZ Scorpion would be just too expensive, although a perfect solution. To best emulate that setup, I?m looking at either the Turnigy AquaStar T20 3T at 128amps or the smaller Turnigy AquaStar 4084-620KV at 106amps. They do have a higher KV version (1050KV), but I think the higher torque version would be better. What do you think of this approach?

What thruster and propeller would you use with these motors to maximize low speed thrust?

[boatsrnew2me]

this man here has done extensive jet surfboard work ,check his videos for tips .he sells jets too but the wait can be awhile

https://youtu.be/xq1vPUhb4qs

[Cativo]

Thanks for the link! Yes, this is a similar approach, although I can?t seem to find any specs on what he?s using other than the ESC. He also fabs his own parts, which is pretty impressive! You are right though, availability is limited.

[boatsrnew2me]

look around the info is there

https://youtu.be/-dTv7zzceto

https://youtu.be/AW6lJHoY4o8

https://youtu.be/kz2DLTlEqdQ

thats the most help i can provide .rest of the research is yours to do .good luck and have fun

[Peter A]

A word of advice, you might be trying to do this with a minimum spend, but you will get a minimum result too. The T20 would be better as far as torque goes, probably on 6 or 8s rpm wise. Another option would be a TP or SSS 56 x 100 motor at around 500kv, more torque on 8 or 10 s. BTW jet units suck a lot of power.

[Cativo]

Thanks for the advice Peter. It goes along the same lines as ?you get what you pay for?.

Your motor choices seem spot on with what Mark discovered too. That SSS 5692 is quite a beast, with its 41 Volts at 300 amps capability giving 12,000 watts! It turned out to be overkill for what he was trying to target, making it less of a good fit, although I wonder if he could have just converted to a single thruster and doubled up on everything, assuming he could find a reasonably priced ESC that can handle 12,000 watts derated for good temperature performance.

I actually don?t understand how the SSS is able to achieve that power while maintaining a similar weight (952g) and size as other comparable units. There is only so much space for windings, and that space grows with higher amperage because of the need for larger wire gauge. I guess better thermal management?

What he eventually settled on that maximized power while meeting temperature, run time and cost targets was the SURPASS Rocket 5692 730KV powered by 9S (down from 12S). He also settled on a Flier 240 amp ESC, a bit overkill but the over-rating helped keep temps low. Although he makes his own impellers, I still don?t know what pitch he chose for this application.

Regarding your statement about jets sucking a lot of power, I thought jets were more efficient because of the drastically reduced slip due to the surrounding cowl?

[Peter A]

Thanks for the advice Peter. It goes along the same lines as ?you get what you pay for?.

Your motor choices seem spot on with what Mark discovered too. That SSS 5692 is quite a beast, with its 41 Volts at 300 amps capability giving 12,000 watts! It turned out to be overkill for what he was trying to target, making it less of a good fit, although I wonder if he could have just converted to a single thruster and doubled up on everything, assuming he could find a reasonably priced ESC that can handle 12,000 watts derated for good temperature performance.

I actually don?t understand how the SSS is able to achieve that power while maintaining a similar weight (952g) and size as other comparable units. There is only so much space for windings, and that space grows with higher amperage because of the need for larger wire gauge. I guess better thermal management?

What he eventually settled on that maximized power while meeting temperature, run time and cost targets was the SURPASS Rocket 5692 730KV powered by 9S (down from 12S). He also settled on a Flier 240 amp ESC, a bit overkill but the over-rating helped keep temps low. Although he makes his own impellers, I still don?t know what pitch he chose for this application.

Regarding your statement about jets sucking a lot of power, I thought jets were more efficient because of the drastically reduced slip due to the surrounding cowl?

What manufacturers state as ratings, well...
For what you want to do you nedd a high volume not high flow pump. That will mean a bigger pump diameter at lower rpm.
Jet units can be more efficient in an application depending on the application, however they still need a lot of power, in that they are not efficient. The lack of slip as you put it means more loading, with electric drive that is watts/amps.