Critique this concept build: surfjet

I am getting older and want a boost when trying to get outside, or to get up to speed on less punchy waves.

It seems like I could add a small tubed propeller and a smallish battery to accomplish this since A) i’ll still be paddling but need some boost, and B) won’t be using the engine for long periods, but in bursts. I don’t want anything under the board and would like to keep weight down.

i’m looking at a 5000mah 12s battery, 200A esc, and one of the kedean jets or waterproof propeller assemblies. water cool the esc with a jet nozzle port. I’d like to be able to control the motor somehow with my body: i.e., maybe a simple small button that i can engage with my chin on the deck to put motor at 90%.

I’ll hollow out the PU, wire up the components and then glass over them.

Not sure how good the kedean jets are, but keep note that a jet does not work well when completely submerged.

the waterproof unit they sell (KED390) :

seems like it’s walking a fine line between a propeller in a tube and a jet. no stator, no details on how they sized the nozzle and the angles on the intake duct.

it seems jets are most efficient at keeping things at speed; my use case here is to give me boost, so i’m already planning to take an efficiency hit vs a prop. I can’t mount a prop in this application because it would mess up the surfing feel on a wave if anything was causing significant drag (i’m already worried about that intake hole of the jet).

however, the nozzle will be above the waterline given the board i’m going to install it on will be floaty and I’m planning to only use the jet while laying flat on the board, not standing up on it…

still trying to find a good battery pack with the right dimensions and bms included. best i can do right now because i’m impatient is a 10s4p, the 12s seem more rare and take longer to ship…

22 to 24 KG Thrust. My dad and I did test last summer with our jet board and got around range too at 15000 rpm on S12. However the amps we pull did go over the 120 amps (per motor!)

Lot of more info here: New (jet board) build discussion thread

ah that thread is great! Good work over there!

I am focused on a single nozzle/jet, single engine design, and while I am heavy (190lbs / 86kg), I will be actually surfing on waves so don’t need this engine to get me up to plane, just push me out past breaking sets or onto a wave :slight_smile:

I’m hoping this means I can use a smaller off the shelf battery pack. Even 15minutes at 80% throttle would be enough for me.

build update: waiting shipment on:

kedean KED390
kedean 200A ESC + custom esc enclosure
eboosted 12s8p skateboard battery

spoke to my shaper, the battery needs to be in a box :frowning:

i’m aiming for a 6’11 pintail surfboard, using an EPS core. will probably throw battery in a waterproof marine bag, and 3d print some sort of structure so the shaper can cut a hole on the deck for the battery.

at this point i’m thinking of 3d printing a “mount” for the esc box so it can be exposed to salt-water on the top and bottom of the surfboard

the jet will also need a harness, but it will be flush with the bottom of the board. I’ll try to 3d print clips that will get glassed onto the board. There will be a large hump on the rear of the board for the jet assembly, and a smaller hump for the exposed esc box.

weight is a concern, but i’m just going to yolo build it and see how it rides.

finally got the jet. still waiting on the battery :frowning:

working with my shaper on sane board design



Looking good, and can’t wait to see it in action.

Very interesting project! Just curious, why did you locate the outlet of the jet as it is now, or will you cut the board so its flush with the outlet?

jet is where it is now due to board thickness and trying to optimize inlet drag. We were going to cut the tail to be flush with the outlet but since this is a prototype i didn’t think it was worth the effort. still waiting for the 5200 to set, but will then do a wet test on a 2-6ft wave and see how it rides.

worried to death about leaks. next build ill do a waterproof USB-c port to charge it and just glass in the battery.

the remote is also not ideal to hold and paddle at the same time, so will also need to figure something else out there.

lastly, I want to figure out a way to cover the jet inlet when the motor is not on (when I’m on a wave), as it will cause a bunch of drag. I’m thinking some sort of magnetic sleeve actuated by a button on the remote but it seems too complex. Anyone have low-tech ideas?

OK. Wonder how much drag in the end the opening will cause, some for sure. Little late now but how about a thin tube closely around the whole jet unit, length to cover the jet inlet. The tube would have a opening for the jet inlet, but when not in use, you would turn the tube and it would cover the opening…maybe not so easy in reality but not much moving parts though.

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I like this idea.

Could spin it with my back foot


What Vefoil did with their jet could be a good source of inspiration, this is an animated Gif:


just did a wet test, the issues:

  1. my hatch fully leaked. luckily i tried to seal all the connections and i latex’ed over the charge port so I didn’t get a fire :slight_smile:. next build i’ll probably glass over everything and leave a suface mount usb-c waterproof adapter for charging.
  2. the remote doesnt work when the board is under water. when i’m paddling on it the esc is mostly submerged and I can only get signal to the esc when I hold the remote right on the deck. this sucks. here is the remote i’m using:

any ideas for the remote?

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I had that remote - it sucks for a couple reasons. At least in the FW version I had (and many others) there is a couple exact positions on the remote that glitch very high or very low due to a bug, nothing like cruising at 30% power and have it glitch to 80-100%…

Reception was pretty bad. I moded the receiver PCB to add an longer external antenna which helped, but was a pain (and with the first issues wasn’t worth it).

brycej, what remote did you end up using instead?

i took it out again. it’s super fun to catch waves but my thoughts so far:

  1. the cavitation with the jet is a minor issue, as i engage the motor over little waves or in whitewater the intake gets air and I lose thrust. a prop would definitely be better. I’m not even sure the drag introduced by using a prop (ideally a folding one) would be that bad when you’re on a wave.

  2. i’m using the most powerful kedean jet with a 12s8p lion and it’s just barely at the speed I want. It’s certainly not enough thrust to get you to be able to stand up without a wave which is fine for me but for anyone considering this jet for an efoil it’s not going to work.

i tried to get some footage of me in action but this is all I could get since i’m just testing it on small days

baby wave:

looks like it is working fine for what you like to use it for.