Another Jet Propulsion Try


#1

Hey Folks,
i want to introduce myself to this great community and share my latest project with you!
My Name is Boris. I am living in the south of Austria, and since i first tried to surf, i ever wanted to find a possibility to surf here in my surroundings… so i built my first electric surfboard in 2016:

It was equipped with a Torqeedo Cruise 4, which i modified to my needs:

All in all i was pretty unhappy with this build… it was expensive, heavy (35kg), slow(20km/h) and had not the surf feeling which i was searching for. So I decided to biuilt a new one…

This time it should be a eFoil, because of many good reasons
less drag results in smaller motors, smaller batteries, and this needs less weight and cheaper components.

As i also wanted to use it on waves to surf and SUP on Lakes with this board, I decided to built it with a jet propulsion.





#2

Hi Boris,

welcome - very nice work :+1:

Is it a MHZ Impeller? What size?

Great idea to make a 2 piece board :star_struck:


#3

Wow, what an intake!


#4

Yes it is a MHZ 58mm Impeller, i thought its a good point to start, as i saw Virus had a similar drivetrain with a 56mm Carbon impeller running with a good performance.

I think a intake funnel will increase the efficiency a bit. At a speed of 40km/h there might be already a noticeable difference.

Today I also got my Foil Kit:
After searching for a while and not knowing which way i want to go (high speed with low drag or low speed with a lot of lift) i decided to look for a system with exchangeable wings.

I also was pretty happy that the mast fits 3x 10mm² Silicon wires and has space left for the cooling tubing.

Also the first parts of the real propulsion unit are on the Printer, I used Collorabb XT, should be tough and temperature resistant enough for most of the components.




#5

I think a little bit of filing of the mast hole will save you from tearing those wires.


#6

Hey MaxMaker,
there will be silicone or an a similar elastic compound between the wires when i do the final assembling, at this point i only tried how the wires fit in the extreme small mast.

I also made further progress in the last few days:

The jet assembly is nearly finished, its already equipped with rotary seals and a angular bearing. I only wait for the aluminium housing which should be ready this week.

I wanted to use this board also as a normal wave SUP, for this purpose the mast should be easily detachable for this reason i made some custom connectors.

Would be nice to hear what you think about it.
Cheers!


#7

nice work, it looks amazing!


#8

Looks like very solid quality to me. The connectors are a nice touch. I didn’t want to try them at the moment because I think the propulsion system will be difficult enough.


#9

which wing from rl-foil you’re going to use?


#10

I bought the allround wing in white, but so far i was not able to try it out, so i can not give a good recommendation at the moment.
Live Update: I am gluing in the foil mounting plate in the next hour, some pics will follow…


#11

I have the Cabrinha double agent. The build quality is good. I have no idea if the wing is suitable, but the good thing is that the wings can be exchanged with two screws. Something to consider before you buy.


#12

Nice work friend only one thing, is no good idea the plastic around the conectors, remove it for other material more temperature resistant. Good jetfoil!
and probably you need more front wing. well try it !


#13

Hi, good job!
Could you tell me if there is a reason for this very small section of the outflow?
I readed that it’s interesting in the air because of the compression of the air, but in the water, there is no compression, so I don’t know if it’s bad or good.

Best regards.


#14

Hey Virus, I just can give the compliment back, i followed your work on Youtube since your first built, and it looks great!

Thanks for the advice! First I printed the part in PLA but as you said that would not be temperature resistant enough, I made a new one out of colorfabb XT which should withstand the thermal load. If not i will machine a new one out of PEEK…

Can you tell me how did you sealed the shaft? I do not really trust standard shaft seals for such high RPM

Regarding the wing, if i need more lift i can easily exchange the wing to the lightwind one…

@hotwireaddict
There is no special reason, it just looks that small because of the big profiled enclosure… but its screw-able so i can exchange it and try out which setup works best.

Current progress, sealing the mast, and gluing in the foil mount.


#15

If you take a NBR 70 you have <12m/s - but if you take a FPM 75 you have <35m/s.


#16

OK, I suggest to try different sizes of the section of the outflow, but not too small, or you will loose pressure.
In the air, a smallest section accelerates the flow for more speed, and a big section increase the static pressure. I don’t know in the water.
Some jet airplanes have nozzle flaps : open for the take-off, closed for maximum speed.

My 2 cents.


#17

In water it is pretty much the same, if you reduce the area of the cross section you increase the flow speed… but the limiting point is can the motor handle the torque which is needed for a small output nozzle, it’s a thing I will optimize when I’m testing the board, because there are to many variables unknown jet…

I do not want to withhold you the current build progress…


#18

Can you tell me what diameter your fuselage has? (Or anyone elses) My Cabrinha has 30mm solid Aluminium. Its very heavy. I want to machine one from carbon fibre solid round stock. Yours looks very sleek. I guess you get what you pay for.


#19

It is about 27mm on the thickest point and I think about 20mm at the smalest… the RL Variofoil is also pretty heavy because of the aluminium mast and fuselage…
Weight is about 3.1kg for the complete assy.

And it was not very expensive: 630€ without tax


#20

Cool job!! I’ve RL mast and fuselage too, ordered a custom 98cm tho. The fuselage with very little adapting could fit Ketos wing or others, bigger than originals.
I really like the mast with connector. Would have copied if I wasn’t already set with the longer cables… Maybe in the next future