Hi everyone,

I've searched for my life for replacement impeller for my Moonraker. The standard impeller is 29mm and 2 blades. I think it perform pretty bad with these. So I wonder if some one knows any other impeller with 4 blades etc.

Thanks for your help!

It appears we have the same problem, I've been going nuts for about 4 months, first trying to buy one and secondly trying to make one. Both were useless. The only Graupner dealer in the US couldn't/wouldn't help and making one had some pitfalls. I'm going to try building one again, but I got frustrated and gave up a few weeks ago. If your in Sweden maybe you can find a Graupner dealer that will help you, or maybe you can call them directly. The guy at the US dealer said that Graupner of Germany wont deal with customers personally, yet they wouldn't help me. Perhaps you will have better luck and if you do let me know. So far the only answer I've gotten was, buy a new drive, lol, a whole drive for an impeller. [:@]

Here a link to my thread about this subject.
http://www.rcuniverse.com/forum/m_5133305/tm.htm

~QS

Hi again,

Ok but is there a 4 blade 29mm impeller from graupner in another jet-system? Check these pictures, looks like it's got 4blades?

[link]http://www.rcgalleri.dk/html/gal_visbil.asp?ID=7206[/link]

What do you think of using 4-blade propeller and cut it down so it fits?

Let's keep eachother updated!

Regards,


Magnus

Not that I know of, I think all the jet-drives use 2 blades, besides that, graupner only makes one kind of the 29mm drive. I too thought of cutting down a propeller, personally I think thats what the impeller is anyway. The only thing is finding the right diameter, my best guess so far is a 40-42mm prop, but it's just a guess. One problem with a 4-blade, is availability. First you need to find a company that makes screw on props and then find a 4 blade performace prop, which I don't think theres many of.

The impeller has to be cut from from a surface prop and I don't know anyone that makes 4 blade. 3 blades can probably be found. Check the Graupner props, but like I said I think they only have 2 blade performance props. Octura might make a 3 blade, but I don't how to attach one since they use a drive-dog. The other problem with an Octura prop, is they're bronze, so cutting it down wont be easy. I dont mean to be pessimistic, but I've already looked into this a bit. I have decided a 3-blade would be best, since a 4-blade simply takes up too much volume in the pump. Again I don't know where to find a 3-blade for this, which was why I was trying to make one.

All the jet antriebs from graupner use a 2 blade impeller.
Replacement impellers should be available, but only the stock 2 blade version.

I made a four blade impeller for the Graupner 2345 jet drive.
It almost immediately burned up my motor...

I have ideas on how to improve the impeller, but it hurts my brain.

One thing I was trying to do with the brass impeller, was reduce the diameter of the hub, I guess that would be tricky with a plastic impeller, since it would reduce its strength. An easy thing to make is a brass stator, that would increase pump volume. Then you could make your hub pointed........that could help I suppose. You guys are making me want to get out the torch again for another try.

My head hurting idea is to actually increase the diameter of the hub from the leading end to the trailing end of the impeller. Water does not compress. So in the design I am attempting, the volume of water entering, has to move faster to get by the restriction created by the increasing diameter of the hub.

This is similar to what the "compression" cone at the back of the drive does to the water stream.
Just a little more agressive. It is working for a gentleman in Japan, Yoichi Takahashi.
So if can figure out how to duplicate his work, I can imagine great success.

hmm, that's the opposite of what I've seen with real boat impellers, but maybe it works. Did he use the same stock impeller, as in the same diameter hub to start with. I could see trying that, but leaving the trailing edge of the hub the same diameter and grinding it down towards the front of the pump. So as not to increase hub diameter overall.

On another subject, some info I found a few weeks ago.
Have you seen those river racing jet boats that use a two stage pump? they have an impeller, which has a propeller in front. I guess it helps prime the pump. These are on what I believe are the fastest jet boats, I have to find a pic. I dont think my application needs one, but maybe it would help yours. But basically it's a lower pitch propeller, on the same hub as the a higher pitch impeller, so they turn at the same speed. The propeller is smaller in diameter than the impeller, which makes sense, due to the change in pitch.

My whole plan was to make the three blade impeller, and matching stator. Then reduce the output nozzle's diameter to increase pressure. Also I planned on shortening the shaft, so I can move the motor closer to the transom. Then move both battery packs to each side of the pump and move the electronics forward. I want to move the cog farther aft, since I read that this is very desirable for high speed jet boats. Unlike a prop driven boat, the jet boat, should have almost all the weight aft, to get the bow out of the water and the intake in the water. I know this really doesnt apply to your boat, but just throwing my ideas out there.

oh btw to the thread starter, how badly damaged is your impeller? I know you want a 4-blade, but you can repair the 2-blade impeller if its not completely shot, that's what I had to do