Speed Coal etc

[Samuel Halpern]

Hey Dave. I got quite a few comments about what you wrote but not the time to delve into lengthy discussions. So I will keep it brief and to the point.

To increase speed you have got to increase steam consumption rate. But if you add more boilers on-line and adjust firing rate so that pressure stays the same you haven't changed anything that the engines would see. The consumption rate of the engines will stay the same because there is nothing to cause it to go up. The supply rate per boiler however would go down.

To increase the consumption rate of the engines you also have to increase the input pressure or change the cutoff. The energy supplied by an engine can be measured off the indicator diagram with shows pressure Vs. stroke in the cycle. Its the area under the resulting diagram that shows energy per cycle. To increase speed you need to increase propeller thrust because the resistance of the ship in the water goes up as the square of the speed. That means the pressure in the cylinders must also go up in order for the energy consumption rate to go up as well for a given percentage of steam cutoff.

As far as Boxhall's 22 knots is concerned, that was a speed over ground that he assumed when he made his calculations. It was probably based on the distance run from noon 4/13 to noon 4/14 which was 546 miles over a period of 24:46 (546/24.8). We know they were carrying 75-76 revs since noon 4/13 untill they added on those extra boilers at 7 PM 4/14. That means she was making just over 22 knots through the water based on Olympic data. As far as those other officers' testimonies, Boxhall said 22, Lightoller and Pitman thought 21.5, and Lowe said 20.95. They were all over the place. In his book, Lightoller later said they making an "easy 22 knots." Sorry if you don't like the way Rowe's reading turns out. We disagree on the time issue which is why you can't get the ship to exceed 21.5 knots through the water. But based on the daily runs, the ship averaged 22 knots over ground prior to noon 4/14 before those extra boiler were even lit. You may also want to check out Kent Layton's fine article: "The Arrival That Never Took Place" regarding this speed issue.

 

[Tim Zukas]

"But if you add more boilers on-line and adjust firing rate so that pressure stays the same you haven't changed anything that the engines would see. The consumption rate of the engines will stay the same because there is nothing to cause it to go up."

There was no separate control of the engine speed-- no governor that could be set to the desired RPM? To increase speed, you increased the cutoff (which increased steam consumption, so you had to increase steam production too) and waited to see what RPM eventually resulted?

 

[Samuel Halpern]

Tim: You are correct in that control of the cutoff was the primary method of establishing the speed of the reciprocating engines. The central turbine responded proportionally to the amount of exhaust being received from the reciprocating engines and it too had no direct speed control. There were Aspinall governors on each reciprocating engine which would cause the throttle plate to close in case of a speed overload situation until the revolutions began to drop. If a propeller blade were to drop, the governor would lock the throttle to the closed position until manually reset. On the turbine there was a Proell centrifugal governor connected to the Brown's engine which operated the two piston changeover valves which would direct exhaust from the reciprocating engines directly to the two condensers should the trurbine go into a speed overload situation.

When set to full speed, reciprocating engines like those on the Titanic would be set to about 85% cutoff. If that cutoff point is unchanged then my point is that increasing firing rate on the boilers or adding more boilers at the same firing rate should cause a slight increase in pressure (and temperature) per boiler and thus increase the total power supplied to the engines. The power to the engines must increase as the cube of the ship's speed. The trust produced by the propellers must increase by the square of the ship's speed since resistance through the water increases at that rate. It's not just the volume of steam going into the engines but also the pressure which results in higher energy consumed per cycle of revolution that is needed to produce the required trust.

Maybe Scott Andrews might have some more to say about all this.

 

[J Kent Layton]

For those of you who may not already be aware of this, my article on the arrival of the TITANIC in New York (Tuesday or Wednesday?) has just hit print in the Titanic International Society's VOYAGE No. 54. The second half of the article will appear in issue No. 55.