I'm trying to create and animate a boat wake, but when I run the simulation and take some renders, I get widely varying and sometimes very weird results: Link to images
These were all rendered from the same simulation at nearly the exact same frame. No settings were changed between renders or simulations, and the simulation was run from the beginning each time. Another thing I've noticed is that, when I've just opened the file and run the simulation for the first time, the results are pretty good. The more times I run the simulation, the buggier it gets.
Also, the "float object" locator is placed outside the fluid containers for the wake emitter (so the floatation is not getting any feedback from the wake).
I'm stumped, so any ideas would be appreciated.

(I'm running Maya 7.0 for OS X, if that matters)