@SoEFoil where can I get such propellor?
Unfortunately, not usable as is. As @borntosurf222 said earlier, those potential candidates have to be scaled down for our use and still to be tested 
Hmmm bad I’m getting close to my finished build but this is necessary
Watch my build pls
Order… 
20char 20char
Is it your 156mm prop ?
1 Like
can you prove the graph is false?
Which diagram? I seem to recal the durajet data was slightly contradictory.
forums are people’s opinions but faking a graph is illegal and could result in fines or a lawsuit.
false advertising, bait and switch, misrepresentation and so on…
the durajet is NOT a jet engine it is more what a ducted fan is to a propeller or a bypass turbo prop for example…I have no desire to argue fyi just to learn 
Yes, with simple logic…
Very few outboard manufacturers bother with Durajet. If it was the best, everyone would recommend them or use them.
Now for simple science…
- With a prop only, all you have in terms of forward resistance at high speed is the foot of the engine and prop. Therefore way less resistance. In addition you can suit prop pitch to motor powerband.
- With Durajet you have a giant shroud around a lower pitch impeller. So one, you need more HP to get to the same speed (more petrol used), two , the giant shroud creates way more forward resistance at speed. Therefore higher RPM, more fuel and less efficiency.
These effects have been shown in all jet drives and even here on this forum when the like of FR takes his shroud off his motors to get his max top speed.
True I have a idea now for a good duct and my build will be finished next week. I will take it one time off for max speed test.
Yeah. Same 156mm prop cnc’d in China. US$150ish plus shipping.
1 Like
Who is faking what ?
Jezza I see the flaw in your logic. Do you have any formal training in physics, fluid dynamics or engineering?
You need a good understanding of wing tip vortices to understand this.
Fluid dynamics and compressibility, withtou that its like trying to understand quantum physics without calculus.
Jezza is convinced Durajet faked their graph.
He maintains people have proven his theory from and said quote:
If that’s from durajet it’s a load of rubbish. On forums it’s already been proved to be Les efficient. If it was more efficient, every motor company would abandon STD props.
and this:
If that’s from durajet it’s a load of rubbish. On forums it’s already been proved to be Les efficient. If it was more efficient, every motor company would abandon STD props.
I personally take a graph published by a manufacturer with more rigour than “forums” but that is just me. Granted durajet has a vested interest but lying in print can be extremely expensive…
Lastly, he is missing a key point but I am patenting the IP so I am not at liberty to explain it, nor do I feel it is my responsibiiility…lol
cheers
Piotr
It was also pointed out that important details were missing from these graphs. If you struggle to be 7% slower at the cost of an extra 15% fuel consumption (or AMP drawn) the number of interested customers will necessarily be low if safety is not the goal.
When could we see the proven benefits of this ? Could it be adapted to efoils ?
Yes in all actually…
But you don’t need formal training to to understand the simplicity of it. A prop with no duct has zero added resistance at high speed.
Durajet has a huge amount of added resistance at high speed. The advantages durajet offers would only be at low speeds and in the realms of safety.
If ducts and jet-drives added benefits in the realms of high speed, all powerboats would use them for racing. It’s that simple.
Your fabled graph doesn’t even indicate what pitch propellor they tested with, which is a huge factor to consider.
If you want to attempt to prove me wrong, build or buy a durajet.
1 Like
Ah so I managed to find the dimensions of the prop that was used for the graph!
Durajet deliberately under-propped the the engine. They used a 13.5" x 11 pitch prop.
That motor normally uses a prop with a pitch somewhere between 13 - 19. That will make a HUGE difference in the stats!
In Canada we cannot have a propeller. So the proven benefit is you are not risking a huge fine, never mind missing fingers and toes.
Jezza has replied as well so I will address my point in that reply since he is bringing up more esoteric information.
As I said Jezza, the graph wuld have to be correct. Nothing else had to be “accurate”.
My original post was to Felix and you included yourself in the discussion which I am fine with but you are overlooking two major points:
- In canada we CANNOT have an open propeller and his post resonated for that reason…
- Safety with 2-4 hp motor has to be the SPORTS number one concern
While I admire your ingenuity and everyone else’s on the forum, water in a control box that turns one of these prototypes into a blender with a propeller set loose among swimmers will create lots of fresh new laws for the sport…NOT A GOOD OUTCOME
THe us military uses them so for them it is the best for a composite of reasons
low speed is precisely what we are interested in compared to speed boats…that was my piont exactly…thank you for making it for me
again thank you showing me where the disconect is…
By reducing propeller blade tip losses, the ducted fan is more efficient in producing thrust than a conventional propeller of similar diameter, especially at low speed and high static thrust level (airships, hovercraft). … Ducted fans offer enhanced safety on the ground.
fluid dynamics is fluid dynamics. i Know at high speed it is the opposite but i dont consider 20 km/h high spped…
The additional shrouding adds drag, however, and Kort nozzles lose their advantage over propellers at about ten knots (18.5 km/h). (LUCKY GUESS BUT OUT BY 1.5 KM?HOUR not bad for a retired guy 
I NEVER ONCE SAID HIGH SPPEDD>>>we are interested in more than a 25 minute ride
and lastly, a durajet configuration with the much larger impeller at half the speed of a normal jet ski because I dont believe they use gear reduction and I doubt durajets pull out the lower end gears and replace them for 1:1 gearing…so I strongly suspect my application of a durajet design will comply with the canadian ana american laws and once a few ppl with your design philosophty donate parts of their bodies to science, it will be a universal almost darwinian type of law because honestly open propellers for foiling seems like the ultimate high risk design compromise…but I digress…
so a much larger impeller than a jetski, at a slower RPM will make this far more efficient than the super tiny super high speed jet drives like the lyft or efoil…would an open torqueedo ultra high efficiency propeller be better yes of course…put that on your boat NOT UR EFOIL!!! unless you like meeting nurses at the ER…
anyway Jezza you do you, my goal is the sport be safer
If you think 10% efficiency is worth people being maimed then I cannot convince you something LIKE the durajet is an option and would not require royalties as it is experied IP
And if you want to as efficient as possible for the last (extra) 5 km;hour t at the cost of people being maimed keep up the good work!