in "real" life there is no way you can totally seal the holes where the propellers or the rudders enter the hull. 
what happens is that you try to have a very narrow gap whre they rotate, with very special bearings and you pump out the water that comes in. 
in "playmo" life a little bit of grease will do the trick blackpearl2006. 
i totally missed this thread and it is a great one. 
i have some "moral" doubts though on adding an engine to a sailing ship (i am a sailing sailor and tend to despise motor-boats). 
2 propellers could do the trick to manouver the boat.
they should run on opposite directions to keep the boat from going sideways and they should be perfectly sinchronized in their rotation speeds to avoid the same problem when going full speed ahead.
this would be a better scheme than to simply attach a playmo-engine and rc a moving rudder (this way you could never stop the boat).
Hmmm...lol, I too have "moral" reservations about adding props to a sailing ship, lol, even for a playmo toy. But even if I equip a playmo ship simply with a rudder and an actuator for turning the sails via slave rig, how would I ever stop the ship? On my Black Pearl custom, my sails can be furled, but unless they make tiny RC klikies that I can remote control to climb the ratlines and furl them, I don't know how else to stop the ship, lol. I suppose you could install actuators that will furl the square sails, but no way to stow the stays and the jibs unless an actuator simply just hoists them up a line (and lowers them.). And I'd need an additional actuator for lowering an anchor.
I actually thought about this; to save on actuators, I could somehow rig the furling motors to be slave rigged to the anchors, so whenever the sails are furled, the anchors drop automatically.
I guess you could stop the ship by steering her into the wind first and then furling the sails. I just thought with motors I can get easier results. But ideally, I would love it all to work like a real sailing ship, as you suggest. I have reservations even with my idea of using a two prop set up with no rudder. I'd go with one prop and a rudder preferably, but I just won this two prop ship for US$10 off ebay and I thought it'd be a good deal. I just wanna see my ship in the water without having to moor it necessarily so it doesn't blow away.
