NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Index corr., Octant as dipmeter
From: Chuck Taylor
Date: 2004 Nov 23, 10:01 -0800
From: Chuck Taylor
Date: 2004 Nov 23, 10:01 -0800
--- Alexandre Eremenko wrote: > >> in the same way our vision is.> I have some experience with naval gunfire during the Vietnam war. When firing from a ship at sea at a fixed target ashore, you need to know the location of the target and your own location with precision. Target location usually came from spotters on the ground or in the air. Within sight of land, nothing beats an optical fix (from bearings of landmarks taken with a gyrocompass and a pelorus). A radar fix can be quite good if the topography is suitable (for example, rocky headlands). Don't forget that radar gives you a bearing as well as a range. Once you know your location and the location of the target, you can compute range and bearing to the target. Then, in order to hit the target, you need to compute azimuth and elevation. That is called the fire control problem and involves the calculus (integration if I recall correctly). That was done using mechanical analog computers (lots of gears). The forward motion of the ship also needs to be factored in, as does the wind, and also the roll of the ship. Mechanical gyroscopes were used to compensate for the latter, so that the gun could be fired at exactly the right instant. The spotters then provided any necessary corrections. This is called "walking it in". I once heard a story about an incident in the Korean War, in which U.S. Army troops 10 miles inland called for gunfire support from a U.S. Navy battleship offshore to destroy a bridge. The Army spotters called in the coordinates and the first round was 100 meters long. The second round was 100 meters short. The Army spotters, who were used to working with Army artillery, started to give the battleship instructions to "walk it in". The battleship responded, "No, we are ready to fire for effect." The next round destroyed the bridge. (A battleship fired a 2,000 pound explosive projectile.) Best regards, Chuck Taylor 48d 55' N 122d 11' W __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com