We all know it's best to have your props turn in opposite directions if you are running two at the same time. But …… Is it better if they are turning outward or inward? I have searched and found a few discussions on it but not enough debate for me to make a decision I thought it was outwards but some one suggested inwards to me and I know some are going to claim in and others out. Is it science or preference or just plain I don’t know why but it just seams better this way. Okay buoys Let It Rip []
I remember reading about this topic. Some of the US armored cruisers had inboard turning props and others of the same class had outboard turning ones. I can't remember which was which but one way gave better speed at a give rpm while the other enhanced low speed manueverability.
IIRC, Some mention of this was made in one of DK Brown's excellent books. I think it said inward turning props (slightly) helped low speed turning by forcing water inward towards the rudder on a single rudder ship. Don't quote me on that though...
In our scale, inward turning props can pull air down the sides of the hull, and cavitate. Don't know if this applies to real life....
We just did the testing on both my new Kumano, and Rick's Admiral Scheer. Both ships with the props turning out at the top, did not turn as well, as turning in, and they both threw alot of water out to the side of the ship, with the prop turning out, instead of directing it to the stern. They did cavatate when the stern was not low enough in the water, the ships were both floating high till we added weight to bring it down to the waterline.
I had suspected that inboard turning props would be better for battling. The stronger flow over the rudder is the crucial factor. (For the record I have single ruddered ships)
I found where I'm accidentally running my Des Moines class with the props turning out at the top, and she maneuvers quite nicely for a ship of her length and single rudder. Not sure when I did that. Must been during a refit when I did that. I'm suspecting that water flipped up into the stern "bounces" back down to the rudder. Would need to put the ship in a basin with colored water to find out what's really going on there. I might want to try flipping those one of these days. My Espana was turning in at the top, and is also very maneuverable. If the props weren't soldered onto the shafts, I might swap them for an experiment there.
My Yamato uses the props to turn inboard as opposed to outboard. The ship turns pretty good this way. I did have it the other way and had equally the same results too. So I am not sure. Hull design below the waterline may dictate some of the factors...
