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Old 09-03-2008, 07:43 PM
Alan Bates Alan Bates is offline
 
Join Date: Apr 2006
Posts: 841
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Bruno, Frank has the right answer. When silt formed on the bottom of the boiler it insulated that spot from the cooling (!) effect of the water. That spot would get hot enough to make the steel more or less elastic. When the steel bagged the silt would break and the water would instantly cool the bagged spot - self-healing, so to speak.

In 1966, I think, the Belle of Louisville bought a pair of Brown Fintube boilers. The back heads bulged during the first trip because the flames reached above the waterline in the boilers. We had to install longitudinal stay bolts from head to head and build a firebrick wall to protect the repaired boiler heads. In two years they were worn out and had to be replaced.

This was caused by parsimony. The board of directors was advised to accept the boilers with the greatest water capacity and the lowest firing rate. Instead, a tightwad on the board held out until they accepted the lowest bid, which was for the lowest water content and the highest firing rate. They were so bad the pilot was obliged to ring for a slow bell when he wanted to blow the whistle! Blowing the whistle could cause water to carry over into the steam line and to the cylinders.

Saving that first expense eventually cost the boat more than two million dollars.

Pilots do not give a hoot about rpm's. They want a particular speed and get it by verbal discussion with the engineer. The engineer has throttle settings for each bell signal.
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