They Were Gradually Working Her Up
We know from the testimony of J. Bruce Ismay
that Titanic started out running at 68 revolutions per minute (rpm) on
her reciprocating engines on her cross-Channel trip from Southampton to
According to Ismay’s recollection, the revolutions carried on Friday, the second day of her transatlantic voyage, were increased to about 72 rpm. At 72 rpm the ship would be making about 21.4 knots through the water. If that increase in revolutions began on Thursday evening at the beginning of the First Watch (the 8 p.m. to 12 a.m. watch), then the average speed through the water between 2:20 p.m. GMT Thursday, April 11, and local apparent noon (LAN) Friday, April 12, averages out to about 21.3 knots, slightly better than the derived 20.98 knots average speed made good for the 484 mile run from Daunt’s Rock to her April 12th noontime position.
Friday evening, April 12, Captain Smith sent a position report from Titanic to La Touraine for 7 p.m. GMT. It read:
Titanic ‘To Captain La
The difference between the time given in the La
Touraine message (7 p.m. GMT) and the time for local apparent noon (1:24
p.m. GMT) was 5 hours 36 minutes. The distance from the approximate noon
position for April 12 (50° 06’ N, 20° 43’ W) to the position in the La
Touraine message (49° 45’ N, 23° 38’ W) is 114.6 miles. The
speed made good calculates out to 20.5 knots for that period of time. But if
Ismay was correct, and Titanic was carrying 72 revolutions per minute,
then the ship should have been making about 21.4 knots through the water all
afternoon. The difference between 21.4 knots through the water and 20.5 knots
speed made good suggests that the ship was under the influence of a relatively
strong easterly component of the
We also have the testimony of Fireman Frederick Barrett that another double-ended boiler was lit up some time on Friday. What time that boiler was connected on line is not known, but we know from Barrett that it takes close to 12 hours to bring a boiler on line after it is lit. Adding just one more boiler to the 20 double-ended boilers they already had connected up on Friday would have increased the overall steam supply rate to the engines by 5%. Thus the power delivered by the boilers for the same furnace firing rate would go up by about 5% which theoretically would result in an increase in revolutions from 72 rpm to about 73 rpm if they kept to the same firing rate. This means that the speed of the ship would have gone up slightly from about 21.4 to about 21.6 knots. If we assume, as they would later do on Sunday, that this extra boiler was lit about 8 a.m. Friday morning, and then connected up around 8 p.m. that Friday night, then we get a weighted average speed through the water for the second day out from Queenstown of about 21.6 knots. With an overall average speed made good of 20.91 knots from noon Friday to noon Saturday, we find that the Titanic was still under the influence of an easterly current drift of about a ˝ knot on its second day out. Clearly, the North Atlantic Current was having a noticeable affect on the progress of the ship this particular day. Is it any wonder that the assistant purser (Reginald Barker) told second class passenger Lawrence Beesley that the 519 mile run for the second day was somewhat disappointing?
For the third day’s run of 546 miles, from noon Saturday to noon Sunday, we have information from both Ismay and Barrett that the revolutions were increased to 75 rpm. This was the minimum revolutions that was called for on Saturday, and Barrett said that he heard of no complaints afterward. It is therefore reasonable to assume that they were making 75 revolutions or slightly better most of the time. We really don’t know what time this increase in revolutions took place, but what we do know is that from noon Saturday to noon Sunday the ship averaged a speed made good of about 22.06 knots. Carrying just 75 revolutions, the ship would have been making a little over 22.1 knots through the water. But we also know from Fireman Charles Hendrickson that at 4 p.m. Sunday afternoon the ship was making 76 revolutions. And all of this was before three more double-ended boilers were connected up that night at 7 p.m. At 76 rpm the ship would be making about 22.4 knots through the water. So an average speed made good of 22.06 knots for the third day out, from noon Saturday to noon Sunday, certainly looks quite reasonable.
Finally, there is evidence that the three remaining double-ended boilers that were first lit up Sunday morning at 8 a.m. were put on line at 7 p.m. that Sunday evening. The reason for adding more boilers on line Sunday was a planned increase in revolutions from about 75 to 78 rpm on Monday if conditions allowed (Ismay). The connect time Sunday night came from Fireman Alfred Shiers who also said that the firemen were told to ease down the firing after these boilers were connected up. The intent was not to let the revolutions increase much above the 75 rpm that was called for when those boilers were first put on line. However, several passengers (Lawrence Beesley, Mahala Douglas, George Rheims, and Henry Stengel) noted an increase in vibration of the engines late that night and assumed that they were running faster than at any other time during the voyage. Some other supporting evidence for this comes from an increase in steam pressure shown on the boiler gauges at 8 p.m. that night (Trimmer George Cavell). If the revolutions had gone up to about 76-77, it would easily explain the 45 nautical mile advance seen between 8 and 10 p.m. by QM Robert Hichens. However, by 11 p.m., it seems that that revolutions once again were registering an average of 75 (Greaser Frederick Scott).
Taking an average between 75 and 76 rpm from 12 noon up until 11:40 p.m., we get an average speed of 22.3 knots through the water, a result which happens to match very well with the taffrail log reading of 260 nautical miles through the water observed by QM George Rowe at the time the accident happened.
 Sir James Bisset (in collaboration with P. R. Stephensen), Tramps and Ladies, first published in the United kingdom by Angus & Robertson, 1959.
 Assuming they increased the revolutions from 70 to 72 at 8 p.m. on Thursday, then the ship’s average speed through the water for the first day out from Queenstown becomes 20.9 knots times 5 hours 40 minutes, plus 21.4 knots times 17 hours 24 minutes, all divided by 23 hours 4 minutes (the total elapsed time from departure at Daunt’s Rock on April 11 to LAN on April 12). This results in an average speed through the water of 21.3 knots.
 The required power goes up approximately as the cube of the speed. Thus the speed goes as the cube-root of the power.
 The additional boilers being lit came from firemen Frederick Barrett and John Thompson.
 Adding additional boilers on line does not necessarily mean an instantaneous increase in boiler pressure or speed. These boilers would be connected up at the same pressure as the other boilers that were already on line. Because of the increased number of boilers connected up, the flow rate of steam from any given boiler would drop allowing for the pressure to build up to a new steady-state value assuming the furnace firing rates remained the same. On these Olympic class ships the furnaces could be fired every 8, 9, 10, 12, 15, 20, 25, or 30 minutes as set by the engineers. For the same furnace firing rate, the boiler pressure would have to increase until a new steady-state is achieved, at which point the engines would be running faster and boiler pressure would level off at the new increased value.