jrll@Portia.stanford.edu (john ralls) (05/12/89)
From: john ralls <jrll@Portia.stanford.edu> >From: royf@roxanne.StPaul.GOV (Roy Forsstrom) >Each shaft/propellor combination is rated at a certain horsepower. Two >shafts with two engines can give you more power with less draft than >with one large prop. Nuclear-powered ships, at 10,000 tons, draw over >30 feet as it is. Each shaft/propellor combination has an engine attached to it which is able to provide a certain amount of horsepower. The naval architect designs the engine, gear, shaft, and prop[ellor to work together to use that power in a way consistent with the mission of the ship. It is true that where draft is of concern, twin screws can reduce the size of the screws, which may, in some hull configurations, reduce draft. But the interest of adding power has more to do with engine size and screw efficiency than draft. The original comment in this thread referred to the Iowa-class BB's. Those ships carry 212,000 hp worth of engine, using old M-type superheating boilers. I think (redundancy issues aside) that it would be challenging to build a reasonable engine which would provide all that power and be capable of the transients involved in shiphandling. On the other hand, the Virginia class CGNs have twin shafts and a total of 70,000 shp. They draw more in the bow (by 7 feet) than in the stern because of the SQS-53 sonar dome. Since the powerr could easily be provided by a single engine (the Ohio class SSBN has similar power on one shaft), the reasons for multiple shafts are obviously not for draft or powerr concerns, but rather for redundancy and maneuverability. There is seldom a single reason for any particular characteristic of a ship. Naval Architecture involves far too many compromises. John
maniac%garnet.Berkeley.EDU@ucbvax.Berkeley.EDU (George W. Herbert) (05/20/89)
From: maniac%garnet.Berkeley.EDU@ucbvax.Berkeley.EDU (George W. Herbert) In article <6501@cbnews.ATT.COM> jrll@Portia.stanford.edu (john ralls) writes: >Each shaft/propellor combination has an engine attached to it which is >able to provide a certain amount of horsepower. The naval architect >designs the engine, gear, shaft, and prop[ellor to work together to >use that power in a way consistent with the mission of the ship. It Small detail: we generally PICK an engine& gear, and have someone else build a shaft and propellor to our specifications. Very few naval architects are also into engine design. Too many moving parts;) We do try hard to pick a set that matches the requirements for the vessel. But getting things to work together is more role and mission related. Mission gives power and propellor type, which leads to a number of useable plants and gear sets...optomize that, run an adequately sized shaft back, stick on mission optomized screw, und viola! ship moves. >There is seldom a single reason for any particular characteristic of a >ship. Naval Architecture involves far too many compromises. Very true, not just of naval architecture. Every structure usually has several reasons and effects, and often has been optimized for non obvious reasons.
military@cbnews.ATT.COM (William B. Thacker) (05/22/89)
From: sun!portal!cup.portal.com!mmm With regard to naval architects and engines, I remember hearing a few years ago that a U.S. warship under construction had been discovered to have incompatible directions of rotation for the engine(s) and propellor(s). (Incompatible with forward motion :-) At the time, it was reported that no decision had been made as to which one would be reversed. Does anybody know which ship had this problem, and how it was solved?
maniac%garnet.Berkeley.EDU@ucbvax.Berkeley.EDU (George W. Herbert) (05/23/89)
From: maniac%garnet.Berkeley.EDU@ucbvax.Berkeley.EDU (George W. Herbert) In article <6767@cbnews.ATT.COM> military@cbnews.ATT.COM (William B. Thacker) writes: >incompatible directions of rotation for the engine(s) and propellor(s). >(Incompatible with forward motion :-) At the time, it was reported that >no decision had been made as to which one would be reversed. >Does anybody know which ship had this problem, and how it was solved? I don't know how or why, but i somehow believe this. In terms of how you would fix it, I would personally just run out and get another prop of the right-turning side. Other option is to drop in a reversing gear into the wrong-twisting side's powertrain. eek. things like this make future engineers crawl into little holes....
esco@tank.uchicago.edu (ross paul weiner) (05/24/89)
From: "ross paul weiner" <esco@tank.uchicago.edu> In article <6767@cbnews.ATT.COM> you write: >From: sun!portal!cup.portal.com!mmm >With regard to naval architects and engines, I remember hearing a few years >ago that a U.S. warship under construction had been discovered to have >incompatible directions of rotation for the engine(s) and propellor(s). >(Incompatible with forward motion :-) At the time, it was reported that >no decision had been made as to which one would be reversed. >Does anybody know which ship had this problem, and how it was solved? I believe that the lead ship of the Avenger MCM class used a differant diesel engine than was procured for later members of the program. It took a while for anyone to realise this engine was incompatible with the reduction gear. My guess is one more gear was added. -- Ross P. Weiner Dandy Dirks Discount Disclaimers esco@tank.uchicago.edu "You can't sue me, I'm broke!"