gonggongboy

I was wondering if enyones used a EDF unit to power a boat. I've seen them with props but never a EDF. So if enyones ever tried one or has thought about let me know how it works.

I was thinking about building a rigger with maybe twin 127mm EDF powered by twin kb45 1000kv on 8s each.

srw1960

its been tried by myself and a couple others..see ducted fan build in airboats.....all have been miserable failures not enough thrust and yes one of the guys is trying a double fan unit and my fan is the biggest most thrust I could find..it pushes it but no wheres fast enough to even call it fun...way way way slow mine is a 89mm fan unit running a 3900 kv brushless motor on a 4s 14.8 volt 30c lipo pack with a 40a esc...im going to give it one more try after I make some minor mods to the hull but im not optomistic

gonggongboy

The one on Hobbycity.com is massive its 127mm or 5in. I say one guys data said its putting out 10pds of thrust each on i believe only a 6s.

srw1960

the way those units build thrust requires speed...they have to be moving and raming air into them to build that kind of thrust...they cant build that much thrust when started when using them on airplanes they work because once thrown into the air and fired up there is very little drag against hte hul to slow it down and its able to build the air speed it needs for max thrust very quicjkly and easily...beleive me after my failure I researched the heck outa this to try to figure out why it wasent working...even a rigger has quite a bit of drag until it gets up on step I dont think the edf units will have enough low end thrust to get it on step...my unit is rated for like4 pounds thrust..the boat weighs maybee 2.5 with everything in it and the fan just blows and blows and blows but no speed...lots of airflow but no speed...like I said im gonna make some hull changes to reduce drag and try it again but id wait and see how it works before ya spend bucks on something that I realy think is gonna leave ya very disapointed...think about it..if it worked good why dont we have a class for edf boats???? or have a bunch of cheap chinese edf's

785boats

I've played around with a couple.
Firstly with a couple on a modified boogie board as a rescue boat. Then I mounted them on a cheap 40"Admiralty cat for a bit of fun.
But it is exactly as swr1960 stated, they need to be travelling fast to be efficient.
Mine were rated at 23A but the 50A escs got really hot after only short runs until one of them managed to melt in the cat. Yep. Smoke & flames.
They were drawing some serious amps because of the lack of speed through the air.
On a rigger however, which should be able to travel faster because of less drag, things would be a lot better.
I say go for it. Especially with the size of the one you have. Mine were only 75mm with 3500kv motors running on 3s Lipo.
Here's a bit of vision for ya.
[link]http://www.youtube.com/watch?v=0o0JRuxilY0[/link]
[link]http://www.youtube.com/watch?v=iLpHQi-456c[/link]

gonggongboy

What if they were mounted on the sides about an inch of the water and angles down about 5-10 degrees.

srw1960

gotta think about what happens to the blades spinning as fast as they are and having water splashed in em..it can knock blades off easy mount it way away from the water.if your gonna try it

gonggongboy

I dont think ill do it. it sounds like it just wont work. My other option was a twin catamaran on 6s-8s with kb45xl 1000-1600kv. I think ill follow through with it alot better pay off.

785boats

C'mon mate.
Don't just rely on my experiences. The reason the ESC blew was because it wasn't water cooled or even air cooled & the fan units were undersized gor the 40" Cat.
I reckon that the size unit you are talking about on a rigger should get up to a fast enough speed to run more efficiently.
Someone's got to try it.
Cheers.
Paul.

gonggongboy

i may after i build my cat since its not much of a lost since ill build the rigger and just use hardware i have laying aroubd but i just lack the knowledge to just go out and do it

785boats

That's the spirit pal. Keep it on the backburner. But don't dismiss it. Read your own signature for inspiration.
Here's a bit more inspiration for you.

[link]http://forums.offshoreelectrics.com/showthread.php?t=8549[/link]

All the best.
Paul.

oceansfiftyseven

Here is my attempt at a little airboat. The first half is with a TT .15 but the second half is with a Midifan and a mega motor. It was all but impossible to point this thing in a straight line. http://www.youtube.com/watch?v=jn4ILCr9_fs

Hijikata

I really like your boogie board design, I have been trying to think of a way to rescue my boats in the less than desirable ponds here in Louisiana. We tend to have a lot of underwater weeds, and I was thinking an airboat design would work... Do you have any more pictures of that rescue boat? Also what EDF were you using? How were you steering it, underwater rudder?

785boats

oceansfiftyseven.
So what does it go like on the water? If you get snow & ice in the winter they are a hell of a lot of fun from what I've seen on you tube.
Looks like it's got heaps of power.

Hijikata.
No rudder. Just reversing brushless ESCs & "tank steering" on a 4 channel transmitter.
The EDFs are cheap Turborix 75mm with 3500kv brushless motors on 3s lLipo.
Here's a link to the build from stage one(with brushed motors & submerged props) to stage three.

[link]http://www.rcgroups.com/forums/showthread.php?t=845000[/link]

Cheers.
Paul.

up_in_smoke

i have a plan for a edf boat that i never bothered to build if your intrested

785boats

Can you post an image of it? I'm sure someone may be interested.

oceansfiftyseven

785boats,
I had it on the water once. It was easier to control but never got her up to speed. Too much power in too small of a boat. It was only 22" long. I love the emergency stop/back-up in the first video by the way.

Hijikata

Thanks for the link 785Boats

srw1960

Did it get on plain? you said you couldnt get it up to speed why not????keep in mind boys and girls drag on a hull running on grass and drag on the water are 2 entirely differant things....grass blades hold the hull up so air can get underneath lot less drag there....

oceans57 where did you get the fan unit your using?? what size and voltage is it brushless????

oceansfiftyseven

The boat had too much torque. Starting the motor would cause the boat to roll dangerously. I did not have the guts to run it wide open. Very fast. I used a 90mm Wemotec Midifan with a Mega 22/30/2 motor on 5S 3700 lipos. About 800 watts. When coming into the dock I was moving too fast and tried to turn. It spun around backwards and smashed the rudders off against another boat. It was very cool. When I do it again, (I have built another, it is a 24" tunnel hull), I will use a smaller fan with less power. I am hoping the tunnel hull will be more controllable. Less spinning out.

small hawk

May be if you were to focus the force from the EDF fan under the water, it might be able to create more thrust then if it was just to stay on top of a boat.

Goldenduff

Edf are used on planes because they allow scale appearance with convenience of electric and cost.

Von Ohain

I second Godenduff here.
EDF was never made for its performance, its made for its scale appearance on jet models.

And for those who care, here is the scientific explaination to why EDF is inefficient.
The thrust a thruster unit can produce is determined by the mass of air or water it can move, times the velocity change it can produce to given mass.

M*V

The energy that is required to produce this trust however is determined by the integral of that very equation.

0.5*M*V²

So, lets say you got 1 Kg of thrust. If you wan't to double that thrust, you can do it by doubling either the mass of air/water you move, or you can do it by doubling the velocity of the mass you are already moving.
But doubling the mass you move only requires you to double your energy input. Hovever, doubing the Velocity of the mass you are moving, will require a quadruple of that energy!

And since EDFs take a small amount of air (small fan diameter) and give it a big velocity (high RPM and steep pitch), an EDF is just ineficcient and rubbish.
Even for fast moving models, a bigger diameter, slower moving propeller would be better (See WW2 fighters, about the fastest things on propellers, and sporting roughly 4+ meter diameter propellers). Big diameter is better, and thats just the way it is. EDFs don't have it.

Goldenduff

I thought edf with a relatively low voltage would power a hovercraft cushion easily - could be a fun project.

Von Ohain

Yep, and EDF can without any problem be used to inflate the cushion of a hoovercraft. It's just not very efficient.
But on the other hand, the EDF is very comapct. Unlike a bigger fan.
Since the cushion fan requires relatively little power anyway, its a tradeoff of how much space you got available, and how much power you are willing to waste for inflating the cushion.
Since the power required is relatively small anyway, I'd say its a fair tradeoff to use EDF for this.
That said, an equally sized fan with much less pitch would function far better for the purpose.