Open eSurf (Request for Comments)

Hi, I’m building a DIY electric surfboard, and I thought I’d open up the components and design for feedback from others. Potentially this could turn into a DIY kit or something.

I’m calling it Open eSurf (link). This link contains a spreadsheet of parts, suppliers, and the board design.

Open eSurf is a work in progress. While I have some experience building drones and other motorized electric vehicles - this is my first jetboard design, so I’m looking for advice on:

  1. comments/suggestions on the selected parts.
  2. suggestions on suppliers.
  3. comments/suggestions on the board design (CAD will be available after I clean I build it)
  4. am I missing anything?

Thanks!

1 Like

you are missing handles, good luck with your project.

I do have handles listed on row 16 of the linked spreadsheet, however I haven’t selected a specific part yet, so it’s not in the CAD atm.

Do you have any suggestions for good handles to use? And recommendations for placement on the board based on riding experience?

Usually two on the sides and one in front and one on the back, your board looks like Radinn Carve so check where they had it…

Yes any tips, advice or analysis on the shape would be greatly appreciated.

The images I posted above are from a couple iterations ago, the latest design is smaller now that I have the parts picked out, but I’m still just winging the shape so lmk how to make it better.

It’s a great point. If it’s a DIY build and not meant for sale, one built-in battery is more than enough for personal use not intended for rentals. I ride Onewheel every day and never needed to switch battery

The main reasons I want the battery removable are:

  1. weight - unlike a onewheel/e-bike, you have to carry this bulky thing to/from the water and removing the battery makes it significantly lighter (~50lbs) and more manageable.
  2. safety - charging on the water seems like a bad idea, and storing the battery in a fireproof box is good practice.
  3. maintenance - I need a way to access the electronics, so what becomes easier/cheaper by making the battery non-replaceable? I still need a water tight lit of some kind, no?

How would it work, specifically? Are you suggesting the battery is permanently fiberglass’ed into the board?

A phone battery lasts all day. Based on the estimated power usage and battery size, this eSurf will only run for 20-30min on a full charge, and take 3-4hr to recharge. If your phone only ran for 30min you’d demand a replaceable battery, no?

WNT, I don’t understand two things about what you’re saying:

  1. it sounds like you are saying the battery doesn’t need to be removable, but then you agreed it needs to be accessible for maintenance, so it’s not clear how you’re proposing it actually be designed, and how that would be easier/cheaper than what I’m planning.

  2. it sounds like you’re saying the motor/jet should be removable for some reason, like the video you posted, but I can’t think of why? the video you linked shows how the same jet system can be used for multiple vehicles, but that doesn’t sounds like something I’d ever do. The motor is already waterproof, so it just needs to be bolted on the board, right?

What I’m proposing for the battery is actually exactly what is shown in the video you sent, a water resistant lid/container in the board for access, and then an inner water-proof battery case that is bolted together similar to a Fliteboard Pro.

We’re talking about an eSurf here, there is a lot of friction on the water so I’m skeptical of your claimed 2hr battery life no matter how well you design the hydrodynamics.

Commercial batteries can’t perform magic, they are typically using the same, or worse cells than I’m planning on using. Specifically, the Molicel P45B cells are among the best on the market today, and no commercial battery has secret battery technology that vastly surpasses it.

There is a nice spreadsheet floating around called ‘eFoil battery calculator’ that I’ve used to estimate a realistic runtime. The nice thing about it is that it provides an estimate in terms of how much energy is required, so it’s independent of how you get there (hydrodynamic improvement, motor improvements, etc).

battery_calc

This is a screenshot of my current estimates. There are really only two variables to play with that make a difference in runtime, the target capacity and the estimated continuous current required (which is affected by hydrodynamics and other factors).

For size/weight reasons, a 18s10p pack of 21700’s is about as big as you can go on an eSurf. The 180 cells alone will weight ~30lbs and much more once you add the bus bars, BMS, wiring, case, etc. So if you try to achieve 2hr by increasing capacity, you would need ~18s36p, which would be completely impractical from a size/weight perspective (well over 100lbs for the complete battery).

So that leaves continuous current as the only viable parameter to increase runtime. I’m currently estimating ~5kW of battery power (75A at 18s) required for continuous operation (on average). A typical commercial eSurf has between a 10-20kW motor, so this seems reasonable, but feel free to provide justification for why it’s not a good estimate. I admittedly just spitballed it, but for reference, to get to 2hr runtime we’d have to achieve ~1.3kW continuous power, which wouldn’t justify the large motors typically found in eSurfboards, so I don’t think it’s realistic.

TLDR, I agree my board shape and motor setup aren’t expertly optimized. However, putting in a lot of effort on optimizing the shape/motor/nozzle/impeller is never going to give a 4x reduction in required power (10-20% improvement is more realistic).

In conclusion, if I’ve made some incorrect assumptions or mistakes, by all means point them out, however it’s not helpful to make wild assertions without providing any details to back it up. If you are in fact an expert in hydrodynamics or impeller design, please provide specific suggestions, simulation results, detailed calculations, etc. Otherwise, please keep the baseless assertions to a minimum.

Good luck with your project friends. From my experience I have not seen any electric jetboard reach more than 30-40 min riding time in perfect conditions. The longest riding time I had with a petrol jetsurf which was 1 hour 10 minutes.

WNT, I’m eager to collaborate with anyone who wants to contribute to the project, that’s why I’ve asked you repeatedly in this thread for specifics of what changes you would make, however I keep getting vague/contradictory claims, and tbh it’s getting exhausting.

This is an exercise in engineering, not optimism. I would love to believe you that it can get a 2hr runtime under some conditions, but the only thing that’s valuable to the project is if you quantify exactly HOW you’re going to 4x the estimated runtime, and under what conditions. Anyone can make claims, but that’s not engineering.

Finally we’d need justification for that the conditions are actually relevant to the project. Are you’re claiming 1.3kW continuous power is enough? If so, does that result in a speed that’s enjoyable compared to the 55km/h other boards do?

I’m sorry if this makes it hard for you to contribute, but it’s what a project like this needs to be successful.

I’ve been working on the board shape a bit. Trying to give it more of a shortboard/surfboard look.

also planning to have some fins on the sides for more stability.

After discovering the DJI propellers were only ~8% efficient, what changes did you make to the propeller shape to get them up to 32% efficiency?

That’s a rhetorical question because anyone would be skeptical of such a claim. If there was some change to the shape of a propeller that resulted in 4x the runtime, DJI, one of their competitors or some 3rd party drone parts supplier would have already made it and dominated the drone market.

This is my point - if someone told you they could make DJI propellers 32% efficient, even though every drone on the market is roughly 8%, you would be skeptical of the claim, and more so when they offer no specific details about HOW such a feat could be accomplished.

That is why I’ve approached your claim of 2hr runtime on the eSurf with skepticism.

I don’t want to keep going back and forth with you about unsubstantiated claims, so I’ll simply say that you are highly mis-informed if you think (in some nefarious plot to maximize profits) that DJI hasn’t put significant effort into highly tuning their drones to balance both flight time and performance. As have the numerous eSurf manufactures that all seem to get 30-45min ride time.

I would like to get this thread back on topic (Open eSurf) and ask you politely to bow out of further discussion unless/until you have something specific to contribute to the project. You have made your claims, I don’t agree with them, let’s just leave it at that.