The current props for the ROV work great, but are designed for a different fluid (air) that is just a tad less viscous than water. So armed withthe thruster testing rig I plan on both charcterizing the existing propeller+nozzle, a bunch of OTS R/C boat propellers, and sourcing/fabricating the ideal propeller+nozzle.
Useful text all about marine propellers and propulsion
(the book is $200+ on amazon btw)
Choosing a nozzle
For the V2 ROV, we want to maximize the the bollard pull (thrust from standstill). By adding a Kort Nozzle, one can increase bollard pull up to 40%; however there are many nozzle profiles to choose from. From "Marine Propellers and propulsion", it seems that a fairly optimal Kort Nozzle is the MARIN no.37 profile, which isn't as efficient as the standard MARIN no.19A in the ahead direction, but is more optimal for both ahead and astern (forwards and backwards) operation (see page
The cross section of the No.37 nozzle is a bit hard to find (you are supposed to pay MARIN a bunch of $$ to get access to them), however I was able to find two grainy scans of it (scan 1, scan 2) and together they form the full picture of the cross section. I plan on making a parametric CAD model of it, so we can make nozzles of any size we want!
Another fitting nozzle design is the Rice Thrust Nozzle, which performance-wise is a bit better than the no.37 profile. However, since Rice has all the patents on it, I'm still searching for a diagram of the cross section.
Turns out that Seabotix uses the No.37 nozzlefor all of their thrusters, and from the looks of their thruster they use a Kaplan type prop.
random websites with info:
I'll continue to post my research/progress here on this page