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tater · 01-06-09, 04:25 PM

I think that is way too fast. The screw count is wrong, too, big, slow props are more efficient. Iowa tried to keep her turns at no more than 200.

0-20 knots needs to take minutes.

Stopping a ship like Iowa is easier than most ww2 BBs because of electric drive. None the less, throwing her all back from 30 knots took over a mile to slow her. (~7 ship lengths). She could stop faster with a "barn door" stop (they could turn her rudders into each other to make a wall—Wisconsin did this once, and suffered for it thereafter, apparently). I have no timing on this, but starting with ~30 knots, that means ~4 minutes to stop.

Stopping should be faster because you also have drag working for you which goes like v^2.

Less advanced designs would have been slower stopping (and accelerating).

IMO, that means the boundary value would be a ship capable of accelerating as fast as she could stop, and that might be 4 minutes from 30 knots—and with an electric drive, reverse was just flipping a switch, you cannot do this as easily with a direct drive.

01-06-09, 04:25 PM	#154
tater Navy Seal Join Date: Mar 2007 Location: New Mexico, USA Posts: 9,023 Downloads: 8 Uploads: 2	I think that is way too fast. The screw count is wrong, too, big, slow props are more efficient. Iowa tried to keep her turns at no more than 200. 0-20 knots needs to take minutes. Stopping a ship like Iowa is easier than most ww2 BBs because of electric drive. None the less, throwing her all back from 30 knots took over a mile to slow her. (~7 ship lengths). She could stop faster with a "barn door" stop (they could turn her rudders into each other to make a wall—Wisconsin did this once, and suffered for it thereafter, apparently). I have no timing on this, but starting with ~30 knots, that means ~4 minutes to stop. Stopping should be faster because you also have drag working for you which goes like v^2. Less advanced designs would have been slower stopping (and accelerating). IMO, that means the boundary value would be a ship capable of accelerating as fast as she could stop, and that might be 4 minutes from 30 knots—and with an electric drive, reverse was just flipping a switch, you cannot do this as easily with a direct drive.