Its spot welded on an industrial grade machine by hand 
we got help by gylling teknikk AS, a Norwegian battery company
I was hoping that you had DIYād it and had some good advice on a spot welder
Had some fun with the efoils today our v1 propulsion unit finally broke down, so we took it off and took it for a tow up behind our v2 propulsion. We are here running the āSeakingā ESC and 12s15p battery pack. Weight 90kg rider on efoil and 70kg on foil board. This is a massive load on the ESC, and we had noe fire, just a bit hotter system. Controlling the Efoil with a rope around the top of the mast is quite tricky, but it works.
We have read about many people that are burning up high amp ESCs, it is smart to test the entire system, not just put in a new ESC. Bad connectors, wires, solder points, water ingress or shorts can also be the cause of ESC fire, and its likely to happen again.
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That is crazy ! So the propeller can pool 2 Foil , the blade area can be smaller no ?
Probably, but its nice to have some power reserve as well. I think this is at the limit of what it will take. If we had gone continuously the entire battery-pack its very likely that something would have failed.
That is pretty amazing. The load must be really high having the drag of two boards. Do you know how many amps you have drawn at maximum?
Any idea what caused the breakdown on V1?
-owner of 2 dead seakings
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The gearbox broke, it was an old used parker gearbox bought from ebay. This one is neugart PLE 5:1. Both our seakings still work great after 50-70H (combined) on the water, one is used with passive cooling, while the other has water cooling.
No logging from the Seaking 
but my guess would be around 4-5000W on takeoff, and around 2500-3000W with both boards on foils.
Do you have cooling lines and 8awg wires running through your mast?
I have a slingshot and it has 3 small cavities about 10mm long and 7mm wide so not enough space for 3X 8awg and 2X 6mm cooling lines. Or are people just running 10awg wires? Or maybe its just this slingshot mastā¦
thanks
Very Interesting. What is the water flow of the pump? Which version (pump/passive cooling) keeps the temperature of the ESC lower?
We use 10 AWG through the mast, we use a hollow bolt (3mm) + nipple to pull water through the bolt cavity in the mast (we just drilled some holes at the bottom above the fuselage threads. Does not take up additional space 
Water cooling is best. This is the pump we use. The flow is not very high, but its sufficient in 20C water. The downside is that you need to rinse it with fresh water every time after use.
Iām using a slightly more powerful pump but my old Seaking ESC always got too hotā¦
Just for my right understanding: If youāre talking about passive cooling you mean having the seaking inside a waterproof aluminium case which is on the bottom of the board?
ah, good idea on the bolt cavities. I was thinking 10awg would be ok too. Iām designing for efficiency and shouldnāt pull more than 40-50A initiallyā¦hopefully less.
Yep, or at the top of the board in this case.
What size prop do you use? We have 142mm on this setup. Large props may draw high motor current (much higher than battery current) that again could damage the ESC .
Iām using your prop scaled to 160mm , 8:1 Neugart ple 40 gearbox, 700kv, 12S, small kite surf foil. My board is really small as well and I couldnāt manage to fly because Iām a bloody beginner. So this means a lot of drag and alot of power. Since Iām using the Flier 320A I now have an almost stable setup for practicing, finally.
Next step is to polish the propeller and change the foil to the SUP foil I bought @Ican (Alibaba). Do you have a step from the mast or the foil itself, I believe we have the same foil because the nice chinese Lady were showing me reference photos also from your build 
Thanks!
Well the prop at that size, and a 700 KV motor will definitely pull a lot more amps than 140mm 500KV setup. That is most likely why you are killing the ESCās.
You shouldnāt need a prop that large. People are foiling with props in the 120mm range.
Are you running the pump constantly or switching it with a temp sensor?
But I have a big gear ratio from 8:1 which should compensate the high rpm, no?
At the prop it compensates it, but at the motor itās still higher which is where it pulls the current. Definitely drop to a 140mm prop and youāll see less current.
What seaking are you using?