Uffff, you are absolutely right 
Sorry I fix it asap
So, i fixed it. Ufff somtimes i… 
Isn’t it better to put a hot insert M8 plus everything than to print in 2 parts and then fly …?
In my V1 version i did it with two parts, every body can do it like he prefere
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What’s the theory behind? Are you just shooting in the dark with this swirl endpiece or are there design criteria or evidence that can be linked?
the same factors should be important as for the prop (diameter/height of swirls, pitch, relative position to prop blades, number of swirls etc)
Ok, that helped a bit, thanks!
Found this:
https://www.sciencedirect.com/science/article/pii/S0141118716305764
I’d like to hear also why a particular design fits for efoil use?
In the paper they tried 120 fin configurations, the best gained about 1% efficiency. I’d say the chances of this being more than a nice visual appearance for us is slim since most of the used efoil props probably can be optimized to give 10% gain without any swirls.
That is my first version.
I will construct more versions, some with less pitch, some withmore pitch and i will also variate the number of blades.
next year i will test it and hope i get some speaking results.
@funboards.at documented in his build thread some results with a propeller without spinner, a propeller with an spinner and an propeller with that spinnerblades.
seems to me very promising.
I can’t be sure since i haven’t so good understanding yet.
My basic question comes from this:
I haven’t seen a single person here doing a theoretic sizing attempt of propeller vs load, i have just seen trial and error method. For me this means that there might be large gains not found yet in motor/propeller combination.
When someone then finds 5-10% gain with a novel design swirl end cap then i wonder how this is verified. Is the propeller optimal before adding end cap swirls? Is the result real?
The poular Metr.at logs won’t be able to prove such a small difference as variation in riding/wing angle/throttle/environment alone could give this. Even motor heating in different runs could cause 5% lower efficiency…
I don’t want to write any academic papers here, nor can I. A camera test in a pool has already proven that the wake vortices can be largely eliminated with this technology. Such a vortex always causes increased energy consumption. A normal spinner should bring about 100 watt savings, a spinner with blades correspondingly more.
Still, 120 simulation runs gained 1% in total efficiency.
The guys in the paper could very well be poor achademics (they’re out there too) but a guesstimate design is not so likely to be better than six scholars focused work.
It’s still interesting, where can i find this video?
Lars, theory is quite simple, but I agree that the fins might only be 1% gain, the rest come from cone.
Industrial shaft propellers normally have very small hubs to reduce drag. In our application it’s about 1/3. Which is substantial. In pleassurecraft this does not matter so much because the drag is minimized through having the exhaust gasses pass though hub and create vortex and pressure equalitation instead.
If you do not have exhaust through hub then you use cone to minimize drag.
Best everyday example is normal stern drives. Volvo penta duoprop vs for instance mercury bravo that use diff ways of expelling exhaust gas.
I have wondered why the commercial props end with a funnel, if it’s for the exhaust gases then i get it. otherwise it seemed like a poor design for drag.
I guess when printing a cone you might as well have the swirls, at least they look nice 
As soon as the epoxy dries, I will do a “battle of the cones” with my 7,4km river testrun.
Roberts cone vs no-cone, so 14,8km in cold swedish waters…
Will post the results here about 17:00.
Will probably have to use the Xmatic app instead of Metr as the latter is still very glitchy.
Thanks @nice2cu Robert for making a nice design, lets hope it’s balanced
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Gentlemen, results are in.
Constants: 100kg rider, whimsi 200L, Axis19 82cm mast. RL 2018 Foil. 14s8P Molicell 42p, trampa 75/300, flipsky 100kv, FR 6x6”.
Conclusions:
- Its really nice to ride in the swedish autumn, when launching from dock and not getting wet at all.
- @nice2cu cone adds +10% energy use. It was also abit more nervous to ride with. Some drops of water also entered the cavity not helping witg balance. Anyways the vanes have to high pitch and are not shaped according prop design. This is the most likely cause. Correct it robert and I will ride it again😉
- I could only ride my cone for a short session and with low batt and also lower avg speed. Even if it shows some advantage avg speed is 4kmh lower then ref, so result can not be trusted. Also 1 vane broke when removing it, so 1mm vanes in ABS is on the weaker side, but it has same pitch as FR.
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Hello Mattias!
Very good! I will correct it ASAP.
When you can test again?
Hi Robert,
Normally ride every second day, but prefer the lively ocean to the boring river…
Can test it in 2 days.
Try using
for base geometry to give some with to the bottom of the vanes and have them sharp at the leading edges.
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just try to straighten the vortex, then you will succeed. Accelerating through too much pitch does not bring any advantages.
Since the resistance in water and air increases exponentially with speed the ”no cone” is the clear winner with the modest consumption at the highest speed.
It would be interesting to have a spinner cone without blades compared.
Do you think you keep the angle of attack and turning curvature and speed constant for three 7km runs? I must say it seems impossible. When you have ten repeated runs all showing lower consumption for a design then it is interesting to compare results.
Overall great effort, it’s better to test than to write on internet forums😀