I guess you can't follow every thread =)
However, to sum up the email i received, FLJ concludes that my model is too heavy, the lead acid batteries unsuited for the task, and the propellers perhaps a little too big. Oh, and, that BEC is not the best thing in the world. I am inclined to agree with this (though, on the BEC-think I have nothing to say). As I have noted before, my only model previously has been a tug (Smit Nederland), where I would say lead acid batteries works like a charm, and the ESC did not fail from too much current, but because of my clumsy installation which allowed for short circuits. I blew four ESCs in that model, before I found out what the problem was; in other words, ESCs and me does not go very well together!
Based on FLJs recommendations I will buy new batteries (two large NiMH-battery packs), a receiver battery, and I still need another ESC. It means, though, that I can continue to use my engines, and now I also know, thanks to FLJ, that having the engine cases connected to each other in the way I have, is no problem.
I must thank you for showing me Action Electronics, and a special thanks to FLJ for his quick and very useful response!