LETTERS
The High-Performance Optics You’re Searching For!
Engineered for navigators who deserve the best! Waterproof Marine II 7 x 50 Binoculars Includes one of the most stable, accurate bearing compasses in its class for easy navigation on rough seas (also available without compass). Fully multi-coated optics and BAK-4 prisms for excellent low light performance with a peak light transmission of over 90%. With Compass–Model 3675493 469.99 Without Compass–Model 3675352 299.99
Compact, waterproof & easy to take with you! Navigator 8 x 30 Binoculars Take these great all-around binoculars anywhere you go! High-performance “CAT” anti-haze lens coating cuts back on the glare that can be such a problem for boaters trying to glass across the water on a bright day.
Model 278098 249.99
Prices subject to change Selection varies by store. Limited to stock on hand. While supplies last.
MORE THAN 400 STORES 1-800-BOATING • westmarine.com Page 82 •
Latitude 38
• May, 2006
⇑⇓DISPLACEMENT IS NOT THE SAME AS WEIGHT I cringe a bit when I hear someone on television saying something like, "The Queen Mary 2 weighs in at 150,000 tons." On page 120 of your March issue, I believe you did something similar. The term 'Gross Register Tons' means size in cubic feet. Each 'ton' represents 1,000 cubic feet — and has no relation to a ship's displacement. For merchant ships, this figure is used for figuring port and canal charges. Fighting navy ships use load line displacement — 2,240 pounds to the ton. I don’t believe the term 'gross' is used with displacement numbers. I believe the term 'ton' originated from the medieval wine casks called 'tuns' that were used to ship wine. A ship was rated by the number of tuns she could carry. Very likely, the QM2 displaces less than the 150,000 plus gross tons listed, as much of the ship above the main deck is made of aluminum. In the case of the Titantic, her gross tonnage was 46,329 (size), while her loaded displacement was 66,000 tons (weight) — but she was built of steel. I must note that the Titantic was the 'biggest ship in the world' then because the forward end of the promenade deck was closed in after some experience of her sistership Olympic (54,524 gross). The displacement of both remained the same. While I’m ranting, allow me to disagree with a spate of learned comments some months ago concerning the effect of displacement on transiting Canal locks. In July 1945, I was a crewman on the USS Colonial LSD 18 transiting the Panama Canal heading for the landings in Japan with a load of some 40+ LCVPss stacked over the well deck. About an hour behind us in the adjacent lock set came the Lurline, painted in Army colors with a load of European Theater soldiers also heading for Japan. The Lurline caught up and passed us before noon. We all believed this was because she displaced about four times our 4,500 tons and thus required less water to be pumped into the chamber. Some days after entering the Pacific, we were told about a bomb that had been dropped — and we were turned back to go to San Francisco where we docked on August 14! Ben Matlick Sunnyvale Ben — As we understand it, there are three different types of displacement — volume, mass, and weight. The first is the size of hole in the water occupied by the ship as measured in cubic meters; the second is the quantity of water displaced by the vessel, and the third is weight of the water displaced by the vessel. To quote the experts, "The displacement weight and ship weight are equal when the ship is at rest in still water. In real life, the displacement weight of a vessel is always changing as it takes on fuel, food, cargo, and people." ⇑⇓WHAT ABOUT MY ANDANTE? I was interested in your March '06 article on the new Latitude trophy to be awarded in the West Marine Pacific Cup for "the boat with the most convincing win relative to its own division" — and how such a formula would have changed the results in previous West Marine Pacific Cups. You might want to look further into the data for the final standings and consider other performance results. In '96, my Island Packet Andante finished first in Division A ahead of Springbok in Division B. The uncorrected elapsed time was 12:04:09:02 vs.13:02:05:20. In corrected time, Andante finished ahead of Springbok winner of B; Stop Making Sense, winner of C; Recidivist, winner of D; and Rollercoaster, winner