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View Full Version : A question with those of you with a nautical bent, so to speak......


Noah Zark.
1st Sep 2011, 01:36
Ahoy, me hearties!
Long ago, I was told that, unlike an aircraft, which has three axis of movement, i.e. pitch, roll, and yaw, a ship has another three, those being heave, surge, and..........? Can't remember the third one. Help, please!
N.Z. Aaaarh!

sisemen
1st Sep 2011, 02:17
sink?.................................

Um... lifting...
1st Sep 2011, 02:22
One believes 'drift' is what you're casting about for.

RJM
1st Sep 2011, 02:38
Ha ha, sisemen.

Could be sag and hog. Sagging is bending downwards in the middle when a wave supports each end of a ship, and hogging is drooping at each end when a wave is supporting amidships. Neither is very good for a vessel.

Mad (Flt) Scientist
1st Sep 2011, 03:07
It's "sway", and a ship and an aircraft both have (like any other unconstrained object) SIX degrees of freedom.

They are:

heave (up/down)
surge (forward/backward)
sway (left/right)
pitch
roll
yaw


@RJM - those are structural modes of the ship, rather than degrees of freedom. They would be analagous to the various flutter modes and structural modes in a plane - also often a bad thing if of any great magnitude

sisemen
1st Sep 2011, 04:51
So what's the difference between sway (left/right) and yaw (left/right)??

I still reckon that the 6th movement is:

http://channel1.natgeochannel.co.uk/Files/Articles/98.jpg

OK - found the real answer!

SUMMARY OF SHIP MOVEMENT
All kinds of ship movement may be divided into three types of linear motion and three types of rotational
motion.

Surging is motion along the longitudinal axis.
Rolling is motion around the longitudinal axis.
Swaying is motion along the transverse axis.
Pitching is motion around the transverse axis.
Heaving is motion along the vertical axis.
Yawing is motion around the vertical axis.

http://www.pomorci.com/Zanimljivosti/Ship's%20movements%20at%20sea.pdf

Firestorm
1st Sep 2011, 06:05
When two or more of the directions of motion combine they conspire to try and make you sick. In my case they never managed, although I did spill a few cups of coffee....

Alloa Akbar
1st Sep 2011, 08:44
Crusty and salty though it sounds.. I have been in a few storms onboard HMS Illustrious (The latest one!!) which like other vessels of her class, moves through the water with a cork-screwing type motion.. That was fun.. Not!:yuk:

tony draper
1st Sep 2011, 09:47
Pogo,longitudinal stretching and contracting of the hull due to going up waves so steep the bow is pointing straight up into the sky.
:rolleyes:
In merchant ships one's cabin always has two places to sleep,the bunk which was generally aligned forard and aft and your settee which was thwartships,one to kip in when she was rolling one for when she was pitching,generally though she did both simultaniously,
Dunno about the Grey Funnel line them poor buggas were still kipping in hammocks on the gun deck in my day, or it they had signed Greek articles two to a hammock.
:rolleyes:

Storminnorm
1st Sep 2011, 11:05
The old fabric covered aircraft used to get Sagging and Hogging.
But that was a long time ago.

lexxity
1st Sep 2011, 11:35
Was going to add corkscrewing to the list, but Alloa beat me to it. :yuk:

Mad (Flt) Scientist
1st Sep 2011, 11:57
So what's the difference between sway (left/right) and yaw (left/right)??

sway is displacement, yaw is rotation.

sway is close to slip/skid in aircraft terms.

"corkscrewing" is a combined mode of several of the degrees of freedom. The aircraft analog would be dutch roll...

sisemen
1st Sep 2011, 13:19
The answer to nautical conundrums? Walk.

Blacksheep
1st Sep 2011, 13:21
When a chap is in his cups he also has those same six degrees of freedom. ;)

Plus the lurch, the trip and the lean.

tony draper
1st Sep 2011, 13:42
We calls that DFCW, departure from controlled walking Mr B.:rolleyes:

Krystal n chips
1st Sep 2011, 14:03
" Surging is motion along the longitudinal axis.
Rolling is motion around the longitudinal axis.
Swaying is motion along the transverse axis.
Pitching is motion around the transverse axis.
Heaving is motion along the vertical axis.
Yawing is motion around the vertical axis "

The above neatly summates the characteristics of every ferry I have been on.......seemingly:yuk:....alternatively, a summation of the flight envelope of the worlds worst aircraft.....the ATP......on a good day.

Take your pick...:E

lasernigel
1st Sep 2011, 14:30
Those high speed catamarans also have a different motion, on the ones I've been on...Bounce!

tony draper
1st Sep 2011, 16:54
Our new Carriers will have a one different from all the above called motionlessness.:)

Noah Zark.
1st Sep 2011, 21:04
Righty hoes, me shipmates. But, befores the nauticalnesses goes aways alls togethers, ones mores questions for 'E all!
If a person of average height, standing on a seashore at the waters edge, is looking straight out to sea, what distance is the horizon thought to be from said person?

Um... lifting...
1st Sep 2011, 21:51
d≈3.856√h where d is in km and h is in m.

Ergo...

d ≈ 3.856 √1.7
d ≈ 3.856 * 1.303
d ≈ 5.024... or call it 5km

Table 8 in my copy of Bowditch says 2.6 miles for 5 feet, 2.8 for 6 feet, 511.6 for 200,000 feet, in case you need that.

And Bowditch being Bowditch, he doesn't fool about much with metres, kilometres, or poncy statute miles. Good honest nautical miles for ol' Nat.

ex_matelot
1st Sep 2011, 22:41
Scientific answer: Monseiur Drapeur was correct - fwd-aft pits are the best.

All the rest is inconsequential bollocks!

Now if you were on a T22 running on both speys and stuck the steering gear motors on...

tony draper
1st Sep 2011, 22:59
Very disconcerting to be lying flat on yer bunk fast asleep and suddenly to find yourself involuntarily sat up and staring down at the floor(deck) that was a wall(bulkhead) ten seconds before.
:uhoh:

Noah Zark.
2nd Sep 2011, 00:59
Thanks for all of the input & info, folks. But do carry on, it's very interesting. My nautical's are as bent as the next man, I'll have you all know!

ex_matelot
2nd Sep 2011, 01:08
"Hands are warned ship is about to cross sea and ship may roll heavily" is the warning pipe issued prior to much fun and excitement commencing.

If stood up fwd the drill is to jump just as the ship falls down a wave, and try to grap a deckhead fixture.

If ship is rolling heavily side to side due to stabilisers being disabled due to stingyness then - gashbag surfing is the order of the day - Find a cross passage, lay a brown paper gashbag on the deck and take a running jumptiming the ship roll also. Kevlar helmets optional but you would be labelled a poof!

RJM
2nd Sep 2011, 01:53
...and I seem to remember that the calculated distances for visibility etc in Norie's Nautical Tables assume a standard height above sea level equal to your shipmate standing on a deck 15 feet above waterline or something.

sisemen
2nd Sep 2011, 02:41
I take it that chucking thousands of gallons of diesel/bunker fuel over the side to calm things down a little during rough times is a bit of a no-no nowadays?

tony draper
2nd Sep 2011, 08:00
Stabilisers!! BLOODY STABILISERS!!small wonder we have bred a generation of milksops!!
:rolleyes:

ex_matelot
2nd Sep 2011, 11:43
It's a scientific fact that on any given warship, my pit would be directly adjacent to one of the stabs. Thats stabiliser will also have a technical problem that causes it to sound like a very large owl every time it moves.

The royal society have even investigated this fact. FACT!

Noah Zark.
2nd Sep 2011, 13:46
Talking of oil on water reminds me that my Granpappy was in a highly secret naval unit during WW2, engaged in shooting U-boats down.
Whilst on convoy escort duties his ship H.M.S. used to patrol all around the convoy, and when a u-boat was known to be in the area, hundreds of gallons of green and blue paint were poured into the sea.
Being oil-based, the paint floated in a thin film on the sea, and when the u-boat upped periscope, a film of blue and green paint smeared across the lens, and the u-boaters, thinking they were still too deep, came up another funfzig feet, and repeated the procedure.
This went on until they were three hundred feet high, then Granpappy's ship shot them down!

Avtrician
3rd Sep 2011, 03:31
I seriously doubt that tale Noah...

Unless of course they were using 20mm Cannons with AP shells...:cool:

Gordy
3rd Sep 2011, 06:06
If a person of average height, standing on a seashore at the waters edge, is looking straight out to sea, what distance is the horizon thought to be from said person?

Well that would be slant range which I believe is:

Slant range in nm=1.23√h(in feet)

Obviously this is more for radio range and as such the heights would be higher...

RJM
3rd Sep 2011, 18:59
um...lifting said:

d≈3.856√h where d is in km and h is in m.

Ergo...

d ≈ 3.856 √1.7
d ≈ 3.856 * 1.303
d ≈ 5.024... or call it 5km

but gordy says:

Slant range in nm=1.23√h(in feet)

= 1.23 * 1.303

= 1.603nm

= 1.603 * 1.852kms

= 2.967...

I don't say anything :bored:

Gordy
3rd Sep 2011, 19:14
2.967 mile [nautical, international] = 5.494 884 kilometer

RJM
3rd Sep 2011, 19:26
no, with respect,

1.603nm * 1.852 (conv factor nm to km) = 2.967kms

Um... lifting...
3rd Sep 2011, 20:18
Neutral corners lads... don't make me get out Doctor Bowditch again.

tony draper
3rd Sep 2011, 21:27
We didn't do furrin kilometers at sea,we used good honest nautical miles as did the chaps who went to the Moon.
:rolleyes:

yotty
3rd Sep 2011, 22:03
Used to have a rule of thumb... eyeball 6 feet above the sea, horizon was about 3 miles.. :)

Um... lifting...
3rd Sep 2011, 22:30
Slant range in nm=1.23√h(in feet)

= 1.23 * 1.303

= 1.603nm

= 1.603 * 1.852kms

= 2.967...

I don't say anything http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wbored.gifMay wish to check your work here, RJM. 1.303^2 = 1.7... but that's in metres, good sir, unless one's using the ship's dwarf for taking sightings. 1.7 feet is about the length of one's forearm and hand.

If using feet, h ought to be 5.8 or thereabouts, making its square root something about 2.4.

1.23 * 2.4 = 2.952nm (meshes nicely with yotty's rule of opposable digit)

2.952nm * 1.852 = 5.46km (rounding errors)

Both gordy & RJM are correct in the conversions betwixt km & nm. Ye're using the same factor.

Don't forget fathoms & shots, Mr. D.

Noah Zark.
8th Sep 2011, 22:18
Just before this thread dies, one more question I can't find an answer to on't t'internet, about ships flags.
Coming back into the Solent from a cruise a couple of weeks ago, the ship was flying the usual flags, i.e. red & white 'pilot' flag, yellow 'healthy' flag, and company flag, but one I have not seen before.
It was simply a black tube, hung vertically. It was a bit like a wind sock, only parallel-sided, and short-ish.
Any ideas, folks?

tony draper
8th Sep 2011, 22:42
Prolly a frock belonging to the Chief Steward.
:rolleyes:

Mad (Flt) Scientist
8th Sep 2011, 23:07
This is from an Australian regulation but I imagine such things are fairly standardized:

Rule 28 Vessels constrained by their draught
A vessel constrained by her draught may, in addition to the lights prescribed for
power-driven vessels in Rule 23, exhibit where they can best be seen three
all-round red lights in a vertical line, or a cylinder

Could that be it?

Um... lifting...
8th Sep 2011, 23:25
Many eons ago, had to know these buggers by heart. And yes, Rule 28 does indeed mention the cylinder.
As to the definition of "Vessel Not Under Command" or "Hovercraft operating in the non-displacement mode", you can read up on it like we poor devils had to.
I will go so far as to say if you see a flashing light, of whatever colo(u)r, one would do well to stay the h*ll away... especially if one's radar plot says it's doing 2-300 knots or so, as it might.

International Regulations for Preventing Collisions at Sea - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/International_Regulations_for_Preventing_Collisions_at_Sea)

Carry0nLuggage
8th Sep 2011, 23:33
What is the reason for the dayglo orange paint on the panel or visor above the bridge windows on merchant vessels these days? I've asked my neighbour about this, but being a Chief Engineer he doesn't see daylight very often and doesn't know the answer.

tony draper
9th Sep 2011, 00:13
I have no idea,ships dont even look like proper ships to me these days.:(

Carry0nLuggage
9th Sep 2011, 00:30
I know what you mean Mr. D. Either floating blocks of flats or overgrown speed boats. No proper style at all.:(