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Re: Bowditch Table 15
From: Bill B
Date: 2005 Jan 24, 20:50 -0500
From: Bill B
Date: 2005 Jan 24, 20:50 -0500
Trevor wrote: > Jim's web page cites George Huxtable as saying that the second term of > the Table 15 equation should be included in the square root bracket. I > am not sure when George posted that information but it might explain why > your results are so different. I believe George to be correct. My Bowditch only includes the first term under the square-root bracket, as I posted it. But that makes no sense to square a number then take its square root without doing anything else to it. Setting up an Excel spreadsheet, it also does not come remotely close to the tabular values. So I calculated it with the second term, then second and thirds terms under the bracket. Adding the second term under the bracket and leaving the third outside matched the table. It's a tiny file, so corrected formula attached. After a sanity check, I do believe it is the distance in nautical miles from the observer to the object. Assume an object 46'tall. I bob it so its top is tangent to the observed horizon and find height of eye to be 6'. Using the quick formula for geographical range, square root of 46 + square root of 6, times 1.17; my answer is 10.8 nm. Using the same procedure my bobbing translates to 0 minutes at 6' height of eye. Correcting for dip, -2.4 minutes as angle used to enter table, with H - h = 40. Plugging into Excel, or interpolating (realizing the table is non-liner), my answer is again 10.8 nm. PS. Have just received George's Post. The stated constants are 0.0002419 and 0.7349 in my copy. But then again, they got the formula a tad wrong. Back to Excel.Bill