Hydrofoil Bike Prop

Hello everyone, I have built a waterbike with foils and have tested it on the water, but my 16(diameter)*10(pitch) inches aircraft propeller seems to be very unefficient. My gear ratio is of 1/4. I am searching a new propeller with a greater pitch for my bike, and i wonder if somebody could help me. I have found the APC marine propellers, some have a pitch of 14, the other ones 17. Do you know what could be better for me ? should I take an aircraft propeller again ? By the way, my lift speed should normally be at 9.3km/h, and when I launched myself from a pontoon (I am launching myself from a beach or pontoon), the prop had zero resistance against water.
Sorry for my bad english.
best regards

 

in general the narrow bladed air craft props are very efficient assuming they can take the power without flexing and of course that they are well match to the conditions.

I am not a prop specialist but would recommend giving us RPM and describing bit better what is the issue and what speed you are having trouble and what is the upper end of the speed range you are looking for (RPM also at this speed).

 

I dont really have a rpm to give, I can only theorise, so I'd say that RPM stays between 200 and 400, which is a really large estimation I assume. In any case, it will not spin very fast, like an aircraft prop. Just for you to know it is a school project before going to university, so I don't have much knowledge, time and ways to calculate loads of things (per exemple Watt for lift speed, RPM etc.). Therefore I know i'm not helping when I can't give you any number to deal with.
The big issue is, there is no resistance when I try to pedal, which means propulsion is not efficient. It can only come from the propeller, but also from the ratio I gave it. I know that a working vehicle similar as mine called "waterbike" on the website Human Powered Hydrofoil https://human-powered-hydrofoils.com/ has approximately a ratio of 1/6. I dont have any infos about his prop.
From what i have red, boat props are bad, because they need to turn very fast. I also know that the props often used for human powered vehicles are aircraft props. But I don't know anything about pitch, maybe you can only find out after testing...
Here is a photo of my current system.
Anyway thanks for any kind of help in the future.
sorry for my bad english,
best regards

 

You can try changing out the derailleur to give you something above 1:4, 16x16 $15, it is probably the smallest draft which many self builders have used. If not, use something larger with as high a pitch as you can like 14 down to 10 or so, but they start to get expensive. A lot of it is trial and within a given range, so if you can find a shop that allows returns, that would keep the cost of your experiments low. A hub with Center Post and side openings can be made that lets you slide the different propellers in and out without having to alter or mark anyting on the propeller- so it can be returned if it is unsuitable. Sometimes there are surprises in efficiency within a particular range which are unexpected. The small props will be cheaper but you would have to go to a higher gear ratios which might be hard to do without losing some efficiency if you go to two stage.

 

@portacruise Thanks for the quick response. Do you think it'd be preferable to have a ratio between 10 and 14 ? or higher ? And what do you exactly mean by get something larger ? Larger blades ?
here is the link of a video of my test :

211009 CycloFoilMonster I.mp4 - Shared with pCloud https://u.pcloud.link/publink/show?code=XZWQa6XZhdRRxbQNMH0aTOgw8N3zqLVxlCy7
its 5 minutes long, in french, the interesting part comes at 1min10 and finishes at 2min55. Be careful the sound may be very loud. On the videos you can see that i am pedalling without meeting any resistance... Hope it can help you to understand my current problem.
best Regards

 

Easiest thing to try is the APC 14 diameter X 17 pitch Marine propeller with your existing 1: 4 system, it does not have to turn fast like a normal wide blade power boat propeller. If that does not work, then the APC 20 diameter X 18 pitch aircraft prop will give even better grip, or what you call good resistance.

https://www.apcprop.com/shop/?product_cat=internal-combustion-engines,marine&rng_min_pa_propeller-diameter-in=14&rng_max_pa_propeller-diameter-in=28&rng_orderby_pa_propeller-diameter-in=number&rng_order_pa_propeller-diameter-in=ASC&rng_min_pa_pitch-inches=16&rng_max_pa_pitch-inches=22-5&rng_orderby_pa_pitch-inches=number&rng_order_pa_pitch-inches=ASC

If neither of those two props work, then you can try changing the derailleur to a 1: 6 ratio.

 

Usually, a 1:6 or 1:7 ratio with a square prop 16 x 16 works well depending on total weight.
There are adjustable pitch airplane props out of Germany that are very reasonably priced.

 

After looking at your test video I suspect this arragement will not work independend of the propeller pitch and RPM. As far as I see your water bike has no floats and the buoyancy generated by the underwater parts like the foils is by far not sufficient to bear the weight if the manned bike (maybe not even the empty one). So the test drivers push the cranks very hard in order to quickly generate bike velocity and lift. But at bike velocity zero and relativ high prop rpm you will not be able to accelerate the water (generating a prop stream) quick enough to gain velocity. Therefore the prop is just turning "a small disk of water" so you feel no resistance.

 

Thank you for all the responses ! I think I'll order a propeller with a pitch of 17. I'd love to know where i could find any propeller with a german adjustable-pitch-prop @BlueBell , for now I have not found anything. @Heimfried I know that starting with a zero velocity speed is not really good, but I must proceed to more tests in order to observe this. For information my bike has a weight of 20kg. Total weight is 90kg, so its quite a lot, but I think the most important thing is drag, that is what probably slows me the most at the beginning. Tomorrow i'll get the bike attached to a boat, so I will definitely be able to know if the foils are working or not. I will also probably observe how hard it is to really start such a thing. Just so that you know @Heimfried , videos of people launching from a pontoon already exists, per exemple these two : so I believe that I can do at least a few meters before starting to sink. If this still does not work, I'll try to add floats, or find a system in order to not start like I am doing for now. I'll send you a video of my future progress, thank you a lot for the help since now everyone !
Sorry for my bad english,
best regards

 

Hold the propeller still and turn the pedals. It looks like something is mechanically slipping.

 

I just tried what you said, and indeed the inside of the propulsion system was not properly fixed ! Thank you very much for the observation ! That means I must test the bike with the same system once again, in order to see if the propeller is really working or not. I still think I must change some things, but there is hope on the horizon...
best regards