Monday, September 10, 2012

Muffler and Bilge Pump Configurations, Pilothouse Glass Thickness

What I learned at the PNW Rendezvous
By Dave Howell, Nellie D. #63

There are at least two waterlift muffler configurations. Earlier tugs (including Titan #30 and Sally W. #42) have a muffler where the inlet is on one side of the can and the outlet is on the other. The muffler is attached under the floor boards and inboard of the starboard water tank. On later tugs (Pet Tug #60 and Nellie D. #63) the muffler's inlet and outlet are both on the top side. The muffler sits in a cutout part of the water tank's inboard, forward section. The latter is a much more complex and costy installation—I can only think that it was for functional reasons the change was made. How quickly the exhaust hose heats up very when raw water flow stops. I could barely keep my hand on Pet Tugs 3" exhaust hose, a foot or so aft of the muffler, meaning it had reached ~115F in the short period between muffler explosion and engine shutdown. 

 In the past week I saw two tugs with bilge pumps forward of the engine and with their respective float switches mounted on top of the pump. Was this where and how the factory installed the pumps? If so, it doesn't make a lot of sense as the deepest point in an LNVT's bilge is under the packing gland. This pump won't turn on until the engine's pan is well under water. 

 In a conversation with Sally and Allan Seymour, aboard the Sally W. #42, Jim Backus suspected that the glass in the two pilot house lowering windows was thinner than the 10mm saftey glass he'd specified. I believe that Nellie's glass in these two windows is also less than 10mm and probably it's true of the rest of the fleet too. So, why are the drop down windows in the pilothouse 5mm (I'm guessing) when they were specified to be 10mm? Perhaps it's because the factory thought the weight of 10mm glass would be too heavy lift and opted for 5mm. So what's the weight difference? Glass weight (exclusive of the wood frame) in a 10mm pilothouse drop down window is 14 lbs and 7 lbs for 10 mm glass. It doesn't seem like a 7 lb difference is worth it considering the safety compromise. But as both Allan and Sally on Sally W. point out, 7 lbs is a lot especially when reaching all the way across the starboard side's chart table. The numbers to support the calculations: 1. 10mm glass weights around 5 lbs/ft^2 2. 5mm weighs 2.5 lbs/ft^2 3. Pilothouse drop down window glass measurement is: 17-1/2" x 23-1/4" or 2.9 ft^2 (per Sally W. #42)

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