Question for the Navy types

[Cobar]

What is the structure that sticks out over the screws on ships like this? LINK

[Steamforger]

Stern and Propeller Guards. These days shrouds are more the norm. In addition to protecting the screw there's also an increase in efficiency in lower speeds and a decrease in efficiency in higher speeds. High or near static thrust can be potentially doubled, but this is highly dependent on the gap between the shroud and the screw.

Basically, good for tugs and large, massive vessels like ferries, submarines, and cargo carriers, but bad for small craft and high speed stuffs. IIRC, Aircraft carriers do not use them.

ETA for wonky stats and mis-remembered numbers. If you really like I can break out Milwee and get wrapped around the axle. Fascinating book, BTW.

[Cobar]

so that lattice work is just there to protect the screws?

[Vonz90]

so that lattice work is just there to protect the screws?

Old style "cruiser" sterns were narrow so a twin screw ship would have the props sticking well out to the side, so if you bumped into something (or vice verse, like a tug boat) you could damage the screw rather easily. This was not a problem for single screw ships because it would be at the centerline.

Modern transom stern ships are much wider in back so there is no issue with the props poking out the side because the stern is well up on both sides.

[Cobar]

Ok, so like fenders over a tire. Thanks always wondered about them.

[mekender]

I believe there was some utility of them being able to protect against things like depth charges falling off the wrong part of the stern too since the Wickes Class did have a single track for rolling the off back there.

From the looks of it they all had them till the Faragut class

[Jericho941]

I believe there was some utility of them being able to protect against things like depth charges falling off the wrong part of the stern too since the Wickes Class did have a single track for rolling the off back there.

From the looks of it they all had them till the Faragut class

Well yes, DDs up through the 1930s also had really narrow sterns.