Allan T Condie
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Steering gear
- Thread starter Colin W. Montgomery
- Start date
Samuel Halpern
Member
Taking the ratios of all the gearing, I get a total leverage advantage of about 168-to-1 (4.83x2.89x12) for the steering engine working on the quadrant. To turn the rudder 40 deg to its hard over position, the steering engine only has to turn about 19 revolutions. Given the size of the steering engine with three 17 inch direct acting cylinders of 18 inch stroke, and steam at 100 psi, I would guess it could easily make 19 revs in under 7 seconds starting from zero. Anybody out there with better data?
Allan T Condie
Member
Methinks your calculations are a bit out and I will have to go and study the steering set-up to check this. Ships I have personal experience with that have steam steering gear take many revolutions to go from midships to hard a port - it has to be this way to get fine control!
Samuel Halpern
Member
Allan: If you have a copy of the 1911 Shipbuilder issue you can count the gears and measure the angles from the detailed diagram that they present.
Cal Haines
Member
Hi all,
Sorry to post and run, but here is reply that I made to the Titanic newsgroup way back when that is on point, hope this helps:
>> "otn" wrote:
>>> Just out of curiosity, can anyone tell me the time required to get the
>>> rudder from hard port to hard stbd for this ship?
There are two things that affect the time: the power of the steering engine and its top speed. If we know the top speed and the gearing we can estimate the minimum time involved; that is the no-load time. We know the gearing, but the top speed of the engine is up for grabs.
"The Shipbuilder" lists the gearing for the Olympic class. There are three pairs of gears involved:
1. engine crank shaft to secondary shaft, 19 teeth to 55 teeth
2. secondary shaft to pinion input gear, 18 teeth to 87
3. pinion to quadrant, 31 teeth on half the quadrant, 14 on the pinion
2.89 revs of crankshaft for one rev of the secondary
4.83 revs of secondary for one rev of the pinion
2.21 revs of pinion to turn quadrant to the stop.
2.21*4.83*2.89 = 30.8 revs of crankshaft turns quadrant from amidships to limit
Tom's speed of 100 RPM for the steering engine crankshaft is probably too low. I have several reference for similar engines running as quickly as 400 RPM; Titanic's electric light engines ran at 325 RPM. I have timed the speed of the steam steering engine on SS Jeremiah O'Brien and it is in the neighborhood of 200 RPM.
at 100 RPM I get 18.5 sec to slew
at 200 RPM I get 9.2 sec to slew
at 400 RPM I get 4.6 sec to slew
(ignoring start up time and lots of other relevant stuff)
The start up time is probably negligible. The steering engines had three 17x18" pistons, all taking 100PSI steam and exhausting to the powerful vacuum of the main condensers. They were built for speed! The O'Brien's steering engine changes directions very quickly. There is less than a one second pause when it changes directions with no perceptible time required for it to get up to speed.
> ... I had two different outbound ships tonight, when I went
> aboard I timed each (electric steering). The older reefer, was 24 sec. The newer
> Car Carrier was 18 sec. ( watching this rudder, I considered it fast). ...
The O'Brien has a quadrant-type steam steering engine that is similar to Titanic's. It takes about 20 seconds, lock-to-lock, while sitting alongside the pier.
One thing to realize is that the time to move the rudder over when running full ahead is going to be greater than the time to return amidships. At some point the engine will begin to feel the force of the sea against the rudder and slow down. As the rudder angle increases, so does the force of the sea against the rudder, so it's the power of the engine that limits the speed. Returning amidships, the force of the sea is working with the steering engine, so it's the top speed of the engine that determines the time. My guess (and it's just that) is that it would take about 15 seconds to swing the rudder hard over; maybe as little as 5 to bring it back.
Another question is how long would it take the helmsman to turn the wheel hard over? Working from a diagram of a Brown's telemotor sending unit, I estimate that it took about 6 revolutions of the wheel to turn it hard over. Unlike some modern ships, the helmsman was working against the large return spring on the receiving telemotor, so he couldn't just give the wheel a spin.
> My problem with the "port around" scenario versus the 37 sec from time of sighting
> to time of impact (is this the correct approximation of time?) ...
That's the "accepted" time, but it's pretty suspect if you ask me. At the American Inquiry, Fleet testified that Titanic turned one to two points to port prior to striking, but that was after refusing to give any estimates as to time or distance. During some of that time he was on the phone to the bridge, so how he was able to provide ANY meaningful estimate of change in heading is beyond me. (Lee would have been in a better position to give an estimate, but I don't think they asked him.) As far as I know there was no compass in the crows nest. Hichens, the only guy who did have a compass, did not provide an estimate of the change of heading at the American Inquiry. By the time of the British Inquiry, both Hichens and Fleet were testifying that the change in heading was two points. The 37 seconds was determined by running Olympic full ahead, putting the rudder hard over and measuring the time it took for her to swing two points to port. The engines WERE NOT run astern, which is odd, since they had adopted Boxhall's version of events, which included running the engines astern. [see Wilding: https://www.titanicinquiry.org/BOTInq/BOTInq27Wilding01.php] I think we have to consider the fact that White Star had a motive to prove that the iceberg was sighted an acceptable distance ahead; Wilding's experiment with Olympic, based on the testimony of Hichens and Fleet certainly gave them that, but how reliable is Hichens' estimate?
>... I find it
> hard to believe there was time to go from a "hard left" turn, shift rudder, check
> swing and start a right turn, in the time allowed.
> Course, without the correct numbers for the rudder and time of impact, everything
> is speculation.
I agree.
Cal
Sorry to post and run, but here is reply that I made to the Titanic newsgroup way back when that is on point, hope this helps:
>> "otn" wrote:
>>> Just out of curiosity, can anyone tell me the time required to get the
>>> rudder from hard port to hard stbd for this ship?
There are two things that affect the time: the power of the steering engine and its top speed. If we know the top speed and the gearing we can estimate the minimum time involved; that is the no-load time. We know the gearing, but the top speed of the engine is up for grabs.
"The Shipbuilder" lists the gearing for the Olympic class. There are three pairs of gears involved:
1. engine crank shaft to secondary shaft, 19 teeth to 55 teeth
2. secondary shaft to pinion input gear, 18 teeth to 87
3. pinion to quadrant, 31 teeth on half the quadrant, 14 on the pinion
2.89 revs of crankshaft for one rev of the secondary
4.83 revs of secondary for one rev of the pinion
2.21 revs of pinion to turn quadrant to the stop.
2.21*4.83*2.89 = 30.8 revs of crankshaft turns quadrant from amidships to limit
Tom's speed of 100 RPM for the steering engine crankshaft is probably too low. I have several reference for similar engines running as quickly as 400 RPM; Titanic's electric light engines ran at 325 RPM. I have timed the speed of the steam steering engine on SS Jeremiah O'Brien and it is in the neighborhood of 200 RPM.
at 100 RPM I get 18.5 sec to slew
at 200 RPM I get 9.2 sec to slew
at 400 RPM I get 4.6 sec to slew
(ignoring start up time and lots of other relevant stuff)
The start up time is probably negligible. The steering engines had three 17x18" pistons, all taking 100PSI steam and exhausting to the powerful vacuum of the main condensers. They were built for speed! The O'Brien's steering engine changes directions very quickly. There is less than a one second pause when it changes directions with no perceptible time required for it to get up to speed.
> ... I had two different outbound ships tonight, when I went
> aboard I timed each (electric steering). The older reefer, was 24 sec. The newer
> Car Carrier was 18 sec. ( watching this rudder, I considered it fast). ...
The O'Brien has a quadrant-type steam steering engine that is similar to Titanic's. It takes about 20 seconds, lock-to-lock, while sitting alongside the pier.
One thing to realize is that the time to move the rudder over when running full ahead is going to be greater than the time to return amidships. At some point the engine will begin to feel the force of the sea against the rudder and slow down. As the rudder angle increases, so does the force of the sea against the rudder, so it's the power of the engine that limits the speed. Returning amidships, the force of the sea is working with the steering engine, so it's the top speed of the engine that determines the time. My guess (and it's just that) is that it would take about 15 seconds to swing the rudder hard over; maybe as little as 5 to bring it back.
Another question is how long would it take the helmsman to turn the wheel hard over? Working from a diagram of a Brown's telemotor sending unit, I estimate that it took about 6 revolutions of the wheel to turn it hard over. Unlike some modern ships, the helmsman was working against the large return spring on the receiving telemotor, so he couldn't just give the wheel a spin.
> My problem with the "port around" scenario versus the 37 sec from time of sighting
> to time of impact (is this the correct approximation of time?) ...
That's the "accepted" time, but it's pretty suspect if you ask me. At the American Inquiry, Fleet testified that Titanic turned one to two points to port prior to striking, but that was after refusing to give any estimates as to time or distance. During some of that time he was on the phone to the bridge, so how he was able to provide ANY meaningful estimate of change in heading is beyond me. (Lee would have been in a better position to give an estimate, but I don't think they asked him.) As far as I know there was no compass in the crows nest. Hichens, the only guy who did have a compass, did not provide an estimate of the change of heading at the American Inquiry. By the time of the British Inquiry, both Hichens and Fleet were testifying that the change in heading was two points. The 37 seconds was determined by running Olympic full ahead, putting the rudder hard over and measuring the time it took for her to swing two points to port. The engines WERE NOT run astern, which is odd, since they had adopted Boxhall's version of events, which included running the engines astern. [see Wilding: https://www.titanicinquiry.org/BOTInq/BOTInq27Wilding01.php] I think we have to consider the fact that White Star had a motive to prove that the iceberg was sighted an acceptable distance ahead; Wilding's experiment with Olympic, based on the testimony of Hichens and Fleet certainly gave them that, but how reliable is Hichens' estimate?
>... I find it
> hard to believe there was time to go from a "hard left" turn, shift rudder, check
> swing and start a right turn, in the time allowed.
> Course, without the correct numbers for the rudder and time of impact, everything
> is speculation.
I agree.
Cal
Samuel Halpern
Member
Hi Cal: Good to hearing from you again. I read your post with great interest and went back to my own notes on this subject. I agree with the count of engine crank shaft to secondary shaft having 19 teeth to 55 teeth, and the secondary shaft to pinion input gear having 18 teeth to 87 teeth. These give the ratios of 2.89 and 4.83 respectively. However, pinion to quadrant count must be handled a little carefully. You are correct in stating 31 teeth on half the quadrant. However, this is much more than a 40 degree turn of the quadrant. If you actually measure a 40 degree turn of the quadrant you will see that the quadrant has to turn almost 19 teeth of travel, not the 31 that are there. This gives a ratio 1.36 revolutions of the pinion to swing the rudder 40 degrees to its stop. Thus, 1.36x4.83x2.89 = 19 revolutions of the crankshaft for 40 degrees rudder swing from amidship. The leverage ratio is computed by noting that if the quadrant would have been a full circle, it would have contained just about 168 teeth. Thus 168/14 = 12 is the leverage ratio for pinion to quadrant. This multiplied by 4.83 and that product multiplied by 2.89 gives a total leverage of 168 to 1 from the steering engine to the rudder.
If still believe it would take about 7 to 8 seconds to swing over 40 degrees. As far as the turning capability of the ship, the famous 37 seconds was a measurement from the time the order was received by the helmsman to the time the Olympic's head veered off 2 points to port. This was at a speed of 21.5 knots with both engines going ahead. The response of the ship, heading Vs. time was probably very close to the following plot adapted from http://web.nps.navy.mil/~me/tsse/TS4001/lectures/11.pdf.
If still believe it would take about 7 to 8 seconds to swing over 40 degrees. As far as the turning capability of the ship, the famous 37 seconds was a measurement from the time the order was received by the helmsman to the time the Olympic's head veered off 2 points to port. This was at a speed of 21.5 knots with both engines going ahead. The response of the ship, heading Vs. time was probably very close to the following plot adapted from http://web.nps.navy.mil/~me/tsse/TS4001/lectures/11.pdf.
Anders Mansfeldt
Guest
Georges Guay
Member
«One thing to realize is that the time to move the rudder over when running full ahead is going to be greater than the time to return amidships. At some point the engine will begin to feel the force of the sea against the rudder and slow down. As the rudder angle increases, so does the force of the sea against the rudder, so it's the power of the engine that limits the speed.»
«Another question is how long would it take the helmsman to turn the wheel hard over? Working from a diagram of a Brown's telemotor sending unit, I estimate that it took about 6 revolutions of the wheel to turn it hard over. Unlike some modern ships, the helmsman was working against the large return spring on the receiving telemotor, so he couldn't just give the wheel a spin.»
«For Titanic running at 22.5 knots, and a full rudder deflection angle of 40 degrees, the force calculates out to 423 tons. Since the underwater area of the rudder works out to be about 402 sq. ft., this force would create a pressure of about 1.05 tons per square foot on the rudder plate.»
Samuel, taking into account the above statements, do you still believe that from a hard over order at 22½ knots, it would take about 7 to 8 seconds to swing the rudder over to 40 degrees?
«Another question is how long would it take the helmsman to turn the wheel hard over? Working from a diagram of a Brown's telemotor sending unit, I estimate that it took about 6 revolutions of the wheel to turn it hard over. Unlike some modern ships, the helmsman was working against the large return spring on the receiving telemotor, so he couldn't just give the wheel a spin.»
«For Titanic running at 22.5 knots, and a full rudder deflection angle of 40 degrees, the force calculates out to 423 tons. Since the underwater area of the rudder works out to be about 402 sq. ft., this force would create a pressure of about 1.05 tons per square foot on the rudder plate.»
Samuel, taking into account the above statements, do you still believe that from a hard over order at 22½ knots, it would take about 7 to 8 seconds to swing the rudder over to 40 degrees?
Georges Guay
Member
I read on the thread that Titanic was equipped with an electrically Rudder Indicator which relayed to the Bridge the real rudder position! On top of the wheel telemotor stand, there was a mechanical pointer that showed the wheel position. Then why install a duplicated electric rudder indicator, if was not to show a possible difference between the wheel position against the rudder position? Was the wheel position attained faster than the rudder position? Was there a Lag Time between the wheel and the rudder?
On a modern electro-hydraulic steering gear system, the wheelsman will turn the wheel over with his little finger in 2 seconds and confirm the mechanical wheel pointer over. Once done, he will look at the rudder indicator. When the indicator pointer shows the rudder over, generally in 14 seconds, he will confirm the rudder over. From the wheel mechanical pointer position to the rudder indicator pointer position, we can say that the lag time is 12 seconds.
What about Titanic?
On a modern electro-hydraulic steering gear system, the wheelsman will turn the wheel over with his little finger in 2 seconds and confirm the mechanical wheel pointer over. Once done, he will look at the rudder indicator. When the indicator pointer shows the rudder over, generally in 14 seconds, he will confirm the rudder over. From the wheel mechanical pointer position to the rudder indicator pointer position, we can say that the lag time is 12 seconds.
What about Titanic?
David G. Brown
RIP
Georges -- you are right that the duplicate indicators were to show the difference between the position of the telemotor and the actual tiller quadrant attached to the rudder. The telemotor wheel on the bridge only opened a steam valve actuating the steering engine which did the actual work of moving the rudder. For some seconds the bridge wheel and indicator would have been well ahead of the rudder. That difference would have reduced to zero once the desired rudder angle was achieved.
The lag time does have some benefit. Ship is not steered only by the resistance of the rudder. Think of the rudder as a trim tab and the hull as a side view of a wing. Tabs on airplanes help generate extra lift. The same lift is created in the water. High pressure helps swing the stern away from the desired direction. This, naturally, swings the bow toward the desired heading. Too rapid an application of the rudder will cause a "stall" condition which actually increases the response time of the ship as it turns to that new heading.
Sam can probably desribe this is spectacular scientific terms. Bottom line, though, is steering is not a slap-dash affair.
-- David G. Brown
The lag time does have some benefit. Ship is not steered only by the resistance of the rudder. Think of the rudder as a trim tab and the hull as a side view of a wing. Tabs on airplanes help generate extra lift. The same lift is created in the water. High pressure helps swing the stern away from the desired direction. This, naturally, swings the bow toward the desired heading. Too rapid an application of the rudder will cause a "stall" condition which actually increases the response time of the ship as it turns to that new heading.
Sam can probably desribe this is spectacular scientific terms. Bottom line, though, is steering is not a slap-dash affair.
-- David G. Brown
Rob Lawes
Member
That depends on who's on the wheel and how good your officer of the watch is.
Regards Rob.
Aaron_2016
Guest
How many seconds roughly would have passed between the moment Murdoch first ordered hard a-starboard to the moment Moody informing him that the helm was hard over? When Olliver reached the bridge he got there in time to see Murdoch closing the watertight doors and see the berg passing aft of the bridge. Yet he was not aware of any helm order before the collision. Was this order a work of fiction?
.
.
Samuel Halpern
Member
The wheel could be turned faster that the rudder as the rudder tried to catch up. It was a standard design at the time for it to take 8 turns of the wheel to shift the rudder from one side to the other. The rudder of course could not get ahead of the wheel because if it did the steering engine would stop and reverse to keep it aligned. They had a name for that type of tracking which I now forget.
The 1922 edition of Lloyds Rules had the 1st requirement that a rudder be capable of going from hard over one side to hard over the other side in less than 30 seconds while the vessel was going full speed ahead. The American Bureau of Shipping adopted the same rule in 1939 and in 1951 the American Bureau adapted 35° to either side as a standard. It was also recognized in tests that there was little to gain in actually putting the rudder beyond 28° as far as responsiveness. My guess is that at angles beyond about 30° the rudder is getting closer to its stall point.
My guess, simply a guess, is that Moody would confirm when the helm indicator showed the helm was hard over.
Last edited:
Georges Guay
Member
«They had a name for that type of tracking which I now forget.»
The Hunting Gear or Follow-up Gear?
«The 1922 edition of Lloyds Rules had the 1st requirement that a rudder be capable of going from hard over one side to hard over the other side in less than 30 seconds while the vessel was going full speed ahead.»
Why did Lloyds implemented such regulation? Did they realise that after a few near misses or accident reports, rudders on these ever growing ships were turning too slowly.
«One thing to realize is that the time to move the rudder over when running full ahead is going to be greater than the time to return amidships. At some point the engine will begin to feel the force of the sea against the rudder and slow down. As the rudder angle increases, so does the force of the sea against the rudder, so it's the power of the engine that limits the speed.»
At 22½ knots, turning from amidships a of 400 ft² rudder at 40 degrees within 7 to 8 seconds, which would generate a force up to 423 tons against a stern inertia of a 50,000 tons displacement vessel, is for the least, impressive! Can you imagine what looked like the cavitations on the rudder turning side! The steering gear was design for hard over orders at manoeuvring speed but positively not for exceptional emergency orders at full sea speed. 7 to 8 seconds at harbour speed would’ve been more than excellent. But at full sea speed, I suspect that Lloyds regulation was not attained?
The Hunting Gear or Follow-up Gear?
«The 1922 edition of Lloyds Rules had the 1st requirement that a rudder be capable of going from hard over one side to hard over the other side in less than 30 seconds while the vessel was going full speed ahead.»
Why did Lloyds implemented such regulation? Did they realise that after a few near misses or accident reports, rudders on these ever growing ships were turning too slowly.
«One thing to realize is that the time to move the rudder over when running full ahead is going to be greater than the time to return amidships. At some point the engine will begin to feel the force of the sea against the rudder and slow down. As the rudder angle increases, so does the force of the sea against the rudder, so it's the power of the engine that limits the speed.»
At 22½ knots, turning from amidships a of 400 ft² rudder at 40 degrees within 7 to 8 seconds, which would generate a force up to 423 tons against a stern inertia of a 50,000 tons displacement vessel, is for the least, impressive! Can you imagine what looked like the cavitations on the rudder turning side! The steering gear was design for hard over orders at manoeuvring speed but positively not for exceptional emergency orders at full sea speed. 7 to 8 seconds at harbour speed would’ve been more than excellent. But at full sea speed, I suspect that Lloyds regulation was not attained?
David G. Brown
RIP
A couple of things which have to be put into the mix...
Speed increases helm response. Less rudder angle is needed for same result.
Titanic's rudder was wide near the waterline where the wake is well aerated and creates less resistance to turning the rudder. It was narrowest down deep where the opposite would be true.
Steering engines on larger ships were massive, being powerful enough to be prime movers in lesser craft. They drove a gear mated to a semi-circular rack on the outside of the steering quadrant. The power was available to make rapid changes in helm angle.
Photograph evidence of the ship's "S" shaped wake indicates Titanic was nimble enough.
-- David G. Brown
Speed increases helm response. Less rudder angle is needed for same result.
Titanic's rudder was wide near the waterline where the wake is well aerated and creates less resistance to turning the rudder. It was narrowest down deep where the opposite would be true.
Steering engines on larger ships were massive, being powerful enough to be prime movers in lesser craft. They drove a gear mated to a semi-circular rack on the outside of the steering quadrant. The power was available to make rapid changes in helm angle.
Photograph evidence of the ship's "S" shaped wake indicates Titanic was nimble enough.
-- David G. Brown
