Hey scubersteve,
I havent testen any shround on my graupner props yet. And you are correct, the SV Seeker video did not show that they do worse in a shroud, he just said that they did.
However, my time has been spent on a slightly different project. I randomly searched Thingiverse (thingiverse.com thousands of things you can download and print) and I found this prop:
http://www.thingiverse.com/thing:338127
As you can read in the description, the creator claims 14N of force @ 6amps, 12volt on a 750kv motor. in both directions! This is above graupner forward performance. And in both directions.
I tried to print this prop, but as it is printed "flat" it needs to be printed with support material witch is slightly more difficult and requires a lot of work afterwards to get a good enough finish where the support material has been removed.
So I made my own version with modular blades. It is now very easy to print. One complete prop took about 55mins to make. To print a set of four blades takes 40mins.
The one I have tested has a diameter of 69mm so it fits the shroud that came with the EDF fan I tested earlier. I can also very easily test different pitch, diameter and twist in the blades.
Tested the first prop now, straight from the printer:
As you can see in the pictures below, the prop doesn't sit deep enough in the shroud so the performance was a little bit bias to the direction where it pulls water through the shroud and out on the "propeller side"
1kg = 5amps
This is pretty much the same as the graupner 2308.65 and quite a bit better then the 4 blade 2311.70 prop.
But, where the graupner 2308.65 prop maxed out at 2,2kg while pulling 12.5amps. This printed prop went to ~3.9kg @ ~22amps (!)
That is a lot of amps, but also a lot of push if you need it
Also, it shows that the performance is quite linear! My tank is a bit too small for the max speed, so the readings are somewhat unstable.
I am sure I can tweak this further, both in the geometry, surface treatment and maybe number of props. But even at this point I believe this prop design beats pretty much everything, especially since it will be pretty close to equal in both directions once the shroud problem is taken care of.