Done another search and found an interesting article about the Volvo and yes, Codprawn, sounds like the props pull rather than thrust. http://www.ybw.com/auto/newsdesk/200...42mbynews.html
Edit: Dunno if I like the sound of this bit but presumably they've done their homework! "In the high-speed scenario, the leg and pod will shear off flush with the hull. The lower bearing carrier has been engineered specially to break at a point below the O-ring seal between the fixed and steerable parts of the drive. As the leg bends backwards, the vertical drive shaft simply pulls out of its spline. The inside of the transmission is now open to the ocean but no water can escape into the boat and the vital mounting joint between transmission and hull will remain not only intact but undamaged thanks to the energy absorption of the big twin O-rings."