Pitot Tube

Glyndwr
14th July 2008, 13:36
When I served as Radio Officer in the Merchant Navy with British & Commonwealth I always relied on the Deck Officers to check the ship's speed and to carry out any maintenance of the instrumentation.

Later on in life when I left the MN I found out a few home truths.....

I found my first job in Italy with Asea Marine. Part of our responsibility was to carry out service on Echo Sounders and Speed Indicators. My very first job was to check the Speed Indicator on MV Zim London. I went along with my mentor who told me that we had to work during the night when the ship was in dry dock. I never really gave this a thought.

When the ship arrived we went on board and tried to pull up the Pitot Tube with a block and tackle - no joy. We went in the dry dock and found out that the Pitot Tube was bent at 90 degrees under the hull. Out came the hacksaw and it took us nearly an hour to saw through the damn thing.

Back in the engine room we managed to pull the rest through and change it with a new Tube. I was amazed to found out that they are 2mt in length!!

We were told by the Chief Officer that "it just stopped working". How many of you out there have committed the sin of forgetting to retract the Tube before entering Port?

Come on own up.....

Anyone got any other stories of this nature.

Glyn

mikeg
14th July 2008, 14:50
My recollection of pitot tube based speed logs (with the Sal in particular) was that the pitot tube wasn't mounted directly under the hull for that specific reason. It was good practice though to retract it when not required which also meant the movement was kept free.

Bent tubes had to be driven out - please would someone remind me, could this procedure be done at sea with the Sal (I seem to remember having done it - but my memory of where is now hazy)

Mike

John Rogers
14th July 2008, 15:20
Many years ago while working around small aircraft one of the duties was to make sure the Pitot Tube was position correctly and alo free of any debris,next to the Pitot Tube was a small tube almost similar to the Pitot Tube,this tube was the outlet for the relief tube located in the cockpit of the aircraft,to get back at any of the pilots that gave the ground crew a hard time they would turn the tube forward into the slipstream. Talk about getting your own back.

mikeg
14th July 2008, 22:52
Many years ago while working around small aircraft one of the duties was to make sure the Pitot Tube was position correctly and alo free of any debris,next to the Pitot Tube was a small tube almost similar to the Pitot Tube,this tube was the outlet for the relief tube located in the cockpit of the aircraft,to get back at any of the pilots that gave the ground crew a hard time they would turn the tube forward into the slipstream. Talk about getting your own back.

A mean trick that would have caused some head scratching and confusion by the unfortunate pilots..however I would have thought that tampering with an aircraft is probably not the best way to get your own back (EEK)

On the aircraft I was flying today (Tomahawk PA38) the pitot tube is situated under the port wing with static vents situated on both sides of the fusalage, in case both of these vents become blocked (by ice or other material) you can switch over to the 'alt static' vent which is in the cockpit.
The pitot tube has a built in heater in case of iceing. One of the ground checks is to switch the pitot heater on for a short while and feel if the pitot tube is getting warm. Obviously its not left switched on whilst on the ground as there is no cooling.

sparkie2182
14th July 2008, 23:10
i sailed on about 6 ships whose pitot tubes were "bent".....awaiting drydock.
on one occasion, when the bloody thing actually worked........it had to be raised/lowered manually as the auto function was long since "shot up".......and would have required reparations of biblical proportions (cost wise) to effect.
on one occasion the act of raising it by striking the moving column with a large hammer (as was the proceedure).........the outer sleeve fractured and caused a serious "ingress of seawater" under some considerable pressure to enter the engineroom.
as was stated later in the "plan of the day"........"what steps did you take?"

"bloody big ones" :)


the evacuation of the space was done in record time............


pass the cement box :)


happy recollections of a completely useless piece of kit.

NoR
14th July 2008, 23:22
There were various types of log when I was at sea. I seem to remember that we weren't over exercised about any of them. the most reliable was the old Walkers Log although you had the hassle of streaming it. Or you could simply get the total revs from the engine room.

I should imagine that these days with GPS that the log is pretty well redundant.

sparkie2182
14th July 2008, 23:25
quite correct about not being "over exercised".......it tended to depend on the mood of the O.M.

as usual.


a modern replacement......... this one being of a specialist nature................

http://www.psicompany.com/furuno-ds30-speedlog/

mikeg
15th July 2008, 10:53
At least the pressure log pitot tube were usually fairly accessible on VLCCs within the engine room compared to some doppler log transducers situated at the bottom of the f'ard tank thus needing BA apparatus and a long climb.

K urgess
15th July 2008, 12:25
Only sailed with a pitot log a couple of times but South Shields Martec made sure we knew all about them. [=P]

K urgess
15th July 2008, 12:31
Doppler was good if you had a sea bed without fish to pick up. Trying to get it to make sense deep sea just because it said it could ("Must be somethin' wrong wi' it, Sparks") was fun. No GPS input in those days to fiddle the results.
Who remembers knowing all about this? (Whaaa)

Had to prove it in the MED exam I took. (EEK)

Glyndwr
15th July 2008, 12:41
Thanks to Marconi Sahib for his excellent contribution.

Going back to my initial thoughts. Was it the responsibility of the deck officers to maintain SALs or did the R/Os do it?
I know that I did not have any dealings with these strange species when serving as R/O. In fact the General Certificate did not breach the line to this sort of equipment.

Am I right or am I dreaming?

Glyn

mikeg
15th July 2008, 13:09
Thanks to Marconi Sahib for his excellent contribution.

Going back to my initial thoughts. Was it the responsibility of the deck officers to maintain SALs or did the R/Os do it?
I know that I did not have any dealings with these strange species when serving as R/O. In fact the General Certificate did not breach the line to this sort of equipment.

Am I right or am I dreaming?

Glyn

Nope you're not dreaming Glyn,
In Shell if the R/O possessed an Electronic Diploma then it was his/her responsibility to maintain the log along with gyro's etc. Usually with Shell if the R/O didn't have the qualification then the 2/0 looked after them ably (one hopes) assisted by the R/O.
As I attended courses on both logs pressure & doppler also gyro's (Anchutz, Browns etc.) it become my territory (Thumb)

Mike

K urgess
15th July 2008, 13:18
Once you got the MED and GTZM managed to palm you off onto some poor shipowner you got the full works. Everything that didn't produce or use steam in the 100s of amps region was yours to love and care for.
Couple of ships I sailed on had no electrician so the 4th Engineer was always screaming for help as well.
Trying to get a generator exciter to work on Christmas morning springs to mind. (EEK)

Kris

mikeg
15th July 2008, 13:52
Once you got the MED and GTZM managed to palm you off onto some poor shipowner you got the full works. Everything that didn't produce or use steam in the 100s of amps region was yours to love and care for.
Couple of ships I sailed on had no electrician so the 4th Engineer was always screaming for help as well.
Trying to get a generator exciter to work on Christmas morning springs to mind. (EEK)

Kris

Same here Kris. Shell didn't employ electricians so as you said anything without steam was yours. Had similiar, drifting in Indian Ocean with two turbo-alterator exciters not working - lost residual magnetism...memories are made of this (POP)

Shipbuilder
27th July 2008, 08:37
My last experience with a Pitot tube was quite funny really. I was just about to get relieved after a 9 months from a ship I din't particularly like anyway. Although we were at anchor, my relief had been put aboard a few days earlier for a totally unneccesary "familiarisation." I was living in the owners cabin & had actually signed off at the anchorage & so considered myself a passenger. As we hauled the anchor in to proceed to port, I was on deck when the ship ,after moving ahead, began to shudder greatly, with lots & lots of light brown mud churning up alongside. Then we moved forward again & began to move normally. Next minute "radio officer please report to the bridge." I didn't go as my relief was already signed on & I was signed off ready to leave in a couple of hours time. After some delay, another broadcast "Mr Wilson please reoprt to the bridge," so up I went. The captain then told me that the log wasn't working and could I have a look at it. I was absolutely amazed & replied along the lines of I couldn't do much about it because the pitot tube has probably gone. "And where precisely has it gone? he asked, "it was OK half an hour ago!" I replied that it probably went when we were temporarily aground. "And what exactly makes you think we were aground?" he asked with rising anger. "All that mud churning up & excessive vibration combined with no forward movement!" I replied as I was fed up with the whole affair (I had been there 9 months) & couldn't wait to go. He thought about it for a moment & then just said "Oh, I see - OK!"

Guess what, I later heard that the tube had, in fact gone!

Bob

John Hunter
1st August 2008, 20:20
I have memories as a cadet with BP in the late sixtees that Nav cadets on some ships went to the engine room to raise the log, I had forgotten the name. I also remember on one ship streaming the log from the stern. After a couple of hours the whole thing had disappeared. We streamed another and sure enough it went missing too. Apparently they were very popular with the crew to convert to lamps!! We did'nt bother again. A CCTV might have been useful had they existed then

Ron Stringer
1st August 2008, 21:55
A CCTV might have been useful had they existed then

Marconis were fitting CCTV on ships in the 1960s. Many of the Manchester Liners' vessels were fitted with CCTV in the bows, to improve visibility from the bridge of the waters immediately ahead. Useful when in transit through locks on their way to and from the Great Lakes (and in their own, home, canal.) Especially useful on all-aft vessels, where the blind spot ahead of the bows could be several hundred feet, depending on the trim.

ChasD
12th August 2008, 22:05
Bent tubes had to be driven out - please would someone remind me, could this procedure be done at sea with the Sal (I seem to remember having done it - but my memory of where is now hazy)

Mike[/QUOTE]

Hi Mike, Yes it was quite common to eject the Sal tube at sea, not difficult essentially pushing the old one out by inserting the new one behind it. It could however cause some excitement if the proper procedures weren't followed, the most important of which was to use the gate valve as a clamp to control the whole thing.
Did come across a report where a couple of E/R Appo's had been given the job, uncoupled the ram, swung the clamps away and at that point found that the tube had been sheared rather than bent. The remnant stub was fired across the engine room like an exocet, followed by the kind of water jet that can only be generated by fully loaded draft at full sea speed. To say that Chief of Engines was not best pleased was something of an understatement ! Halia used to spit these things out on quite a regular basis. Did a fair bit of early research on doppler logs on Drupa, especially into the effects of the "barrier layer" - the slice of turbulent water that exists between that water being dragged along with the hull and the main body of the sea - get all sorts of silly effects from this, one of the main reasons why doppler logs go haywire from time to time. All part of the fun, I used to enjoy the heavy hammer stuff from time to time as a change from the soldering iron!

vasco
13th August 2008, 02:13
I should imagine that these days with GPS that the log is pretty well redundant

Far from it surprisingly.

Radars require the speed through the water (log) to accurately plot other ships courses, speed and collision prospects.

The GPS provides the speed over the ground.

For the un-iniated, if a ship is tied up at a berth then the GPS speed will be 0 but the log will read whatever the current is.

As for maintenance I spent many a miserable hour adjusting the Sal in the pit to get the speed right for the new fangled True Motion Radar on my first trip 2/O. Remember it was all to do with graphs and vernier scales. Of course, the fact the pipes were choked full of salt did not help.

Vital Sparks
13th August 2008, 08:00
I had to replace a pitot tube that had been cut off. Navigator forgot to withdraw the tube before we entered the frozen Baltic.

Naytikos
22nd October 2008, 07:57
I know I had a Sal-Log on more than one ship but can't remember if that is the one with the rubber probe that senses the magnetic field of the passing water, or the one which was a simple tube allowing the water up into an electromechanical device and you had to bleed the air out every week or so. Either way I always wore the absolute minimum when handling the pitot tube as it would invariably lead to a soaking.
Once had a Sperry doppler-log which was supposed to reflect off a layer of seawater they claimed existed 50 or so feet down where there was a temperature shear line. How this was intended to function with a laden draught of 80 feet the manual didn't say! I managed to get it to display random speeds which vaguely corresponded with Full and Dead Slow and no-one cared what happened in between.
I always found that if a piece of gear was operated by turning a switch or pushing a button, then I was expected to make it work. Great fun!

sidsal
10th December 2008, 16:34
In my day pitot tubes were unknown. I came across them of course in my flying career.
I was on a ship , the MATHERAN in WW2 and unusally we had ASDIC and carried a naval operator. She also unusually carried depth charges on the poop. On passage Colombo to Calcutta we got a strong signal - ping - ping and we must have passed right over whatever it was. Probably a Jap sub.
Anyway the master, despite urgings, did not drop depth charges and was, I believe reprimanded for not doing so. When she went in drydock in the UK some time later they forgot to withdraw the sticky out thing and so the lot was stripped out of her.