So here is the video introduction for my build where I discuss the general plan and the components that I got so far for this build. I hope this gives a good overview. Especially for people that are new to this.
Here is the CAD model:
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I did 2 patches near the mast, and 2 full layers on top and bottom overlapping each at the sides. The colour is just there so It gives a bit more contrast. This will all be paninted soon. But first I need to do a lot more filling and sanding. I also have to patch a few spots. Overall I am quite happy so far.
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Very cool board! I’ve seen the video, allow me one thought about the Mosfet power switch: I ordered one from a Russian guy on Esk8 forum, the Vedder model with 5 mosfet, 100A capability, with fuse, he discouraged me to use that as safety switch because the ESC won’t be happy to cut down under load… he got me the part at very special price “for research purpose” to see if I would have tried to fry my ESC.
I will use that as main switch just to arrive at the beach with the batteries already in, to avoid messing with battery case in sand, dirt, water… just press a button and arm the system. Basically it’s a battery isolator which you manually use in case anything goes wrong but not attached to a lanyard kill switch. I’m still thinking about a feasible and affordable solution…
Here is an update. I cut the foam in three layers and glued it together. Then I sanded everything smooth and coated with 2-4 layers of fibreglass.
Then followed two weeks of sanding, filling, waiting for the epoxy to harden, sanding and more filling. I spent 90% of my time sanding and filling holes. I used 30 disks of 60 grit sandpaper. Maybe the 3M stuff is worth it? Its very important to get 100% glass adhesion. Any tiny spots without adhesion will become holes in the sanding process and need to be filled.
It is currently beeing painted.
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whats the reason to put the accu so far to the front?
Several reasons.
- A lot of people here told me to do it further forward.
- The box is proud of the board, so I cannot put my feed there. Placing it forward gives me enough space.
- Pacificmeister has is up front.
- I have no idea how to ride that thing, so i had no preference.
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Hi @MaxMaker, great work! Regarding my battery position, you are correct if you refer to my very first tests where I had the battery box strapped to the front. It’s now in the center in between my feet. Good luck with the build!
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Yeah, but I also think that most riders at the moment have to place a lot of weight at the tip to counteract the moment from the back wing. That is because most wings are designed to be pulled by a kite or a boat, so the force is acting high above the board. With the motor, the force is on the opposite side. So I will probably build new wings one day that are optimized for an efoil.
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The paint job is almost done. There are only some minor touch ups left. Then comes the clear coat, but first I want the paint to cure for a few days.
The bronze on the nose was a bit tricky. I couldn’t buy the right colour, so I used metalic copper and mixed it with black. It took a few tries until I got it right.
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That’s quite a hell of a solenoid! Seems an Albright single contact. We use those at work for powerfull DC thrusters and winch motors.
For Lipos and ESC I’m still concerned about the huge sparks they trhow and the effect of a sudden break up under load over ESC Mosfet… but only by trying you can find out. Finger crossed.
It is an albright and they use it a lot for forklifts in case you want to shop one on ebay. Solid build quality.
I will add anti spark somehow. At the moment I am thinking about adding a secondary relay that only connects while the big relay is connecting. This would be controlled by an Arduino. After it is connected, the secondary relay will disconnect again, so it doesn´t pull any current. This will all happen in 1 second or so. Resistor specs are welcome!
short: A 50 Ohm, 5W resistor is good enough. If you want to build a compact device a 3W resistor with 47 or 51 or 56 Ohm resistor will be fine, too. Search for cemented wirewound resistors.
Examples: 5W or 3W or search your favourite distributor 
Your second relay can be quite small as the peak current is obviously only 1A.
Why I would choose a ~50Ohm resistor:
To calculate a resistor you can use this website: https://www.allaboutcircuits.com/tools/capacitor-Charge-and-time-constant-calculator/
I have 8 x 480uF on my ESC, the new Vesc 6 has 1360uF of total input capacitance. If you decide on what ESC to use, look at the electrolytic capacitors on the input to find a closer value. I just assume 3000uF to be on the safe side. That is the capacitance you have to charge with your antispark mechanism before you connect your big relay. Assuming 50V battery voltage I just trimmed the resistance value until my time constant was in the right range. After 5 times this constant your capacitor can be assumed to be fully charged. Reading your post I assume your goal ist to be faster than one second. With 50 Ohms as charge resistor your max charge time would be 0,15s*5=0,75s. Peak power is 50W, but you probably only need a 5W resistor as after about 0,2s the power is below this value and the power dissipated is quite low (<4J). This datasheet has good graphs startig on page 5 for what shorttime overload wattage is acceptable. As all assumptions above are quite conservative a 1W resistor will work, but the cost is not significantly lower for a one off device and you probably don’t want to order twice.
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The paint is done. A few coats of spray paint followed by clear coat. The texture is a bit more rough like it was supposed to be. Somehow the paint didn’t form a nice even wet coat. Its looks a bit like a fine orange peel. I could sand it with fine sandpaper and then polish it, but I think I leave it as it is. If I sand through the paint there will be spots to repair which will just add a ton of work.
It weighs 3.8kg at 150x50x14cm.
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So that is a volume of 105 liters, correct ? With a concave shape, as 50cm width must be the max width in the middle…
So that must be slightly under 100 liters all in all
I hope that you do not weigh as much as me 
Actually its just 70l the cavities and the thin nose take out a lot of volume. I weigh 83kg. 90kg with my vest, wetsuit, helmet and shoes.
15 kg hardware + 90 kg of you… That is 105 kg for a 70-liter board. Ouch.
You’d better start going on diet 
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Looks fantastic, congrats on the high quality build.
Are you planning on installing a hatch over the compartments?
Thank you. The compartments will be filled with a waterproof camera case and a waterproof aluminium enclosure for the ESC. They will be strapped in with nylon webbing.