Transcript Sideswipe or Grounding?

Sideswipe or Grounding?
Titanic's Impact With the Ice and Its
Immediate Aftermath
PART 1 OF 2
Drawing done by S. P.
Skidmore, April 15, 1912,
aboard S.S.Carpathia.
by Samuel Halpern
Revised, Wednesday, 22 August 2007
PRESENTATION OVERVIEW
 Some observations
 Ice in the well deck
 Center of Buoyancy, Center of Gravity, and Metacenter






The impact force vector
Sideswipe or grounding?
Underwater contact sequence
Calculating maximum impact forces
The initial list to starboard
Down by the head - a sequence in time
A Titanic Myth
"The vessel took the blow of a deadly, underwater, projecting shelf of
ice, on her starboard bow near the bridge, and before she swung clear,
the mighty ram of the iceberg had torn its way through plating and
frames as far aft as amidships, opening up compartment after
compartment to the sea." - Scientific American, April 27, 1912.
Grounding on a Submerged Shelf of Ice?
Article From The Sphere 27 April 1912
Some Observations
Passenger Jack Thayer
"I wound my watch-it was 11:45 PM-and was just about to step into bed, when I seemed to sway
slightly. I immediately realized that the ship had veered to port as though she had been gently
pushed. If I had had a brimful glass of water in my hand not a drop would have been spilled, the
shock was so slight."
Leading Fireman Frederick Barrett
"The water came through the ship's side...about 2 feet above the floor plates, starboard
side...She was torn through No. 6 and also through 2 feet abaft the bulkhead in the bunker at
the forward head of No.5 section."
Fireman George Beauchamp
"Water was coming in on the plates when we were drawing the fires...coming through the
bunker door and over the plates...coming through the bunker like."
A 25 ft pressure head
would produce a stream
that reached as far as 15 ft
across before falling on
stokehold plates 2 ft below.
Drawing shown is to scale.
A Few More Observations
Lookout Reginald Lee
"The ship seemed to heel slightly over to port as she struck the berg...Very slightly over to port,
as she struck along the starboard side."
Lookout Frederick Fleet
"She listed to port right afterwards...a slight list...just afterwards [of striking the berg]...[Did it
seem that the blow came beneath the surface of the water that caused her to shift over to port?]
Yes."
AB Seaman William Lucas
"I had just left the mess room...It very nearly sent me off my feet."
Passenger Major Peuchen
"I had only reached my room and was starting to undress when I felt as though a heavy wave
had struck our ship. She quivered under it somewhat. If there had been a sea running I would
simply have thought it was an unusual wave which had struck the boat."
Fourth Officer Joseph Boxhall
"She was doing Full Speed and it didn’t break my step."
Ice in the Well Deck
Lookout Reginald Lee
"As she struck on the starboard bow there was a certain amount of ice that came on board the
ship. That was the forewell deck. It seemed as if she struck just before the foremast."
Deriving Distance From Center of Buoyancy To Metacenter
For Rectanguiar Cross-Section Hull
Deriving Heights of Center of Buoyancy, Center of Gravity,
and Metacenter on Titanic for April 14, 1912
Six Degrees of Freedom
• Three translations of the ship’s center of gravity (G) in the
direction of the x-, y-, and z-axes:
– SURGE in the longitudinal x-direction, positive forwards
– SWAY in the lateral y-direction, positive to port side
– HEAVE in the vertical z-direction, positive upwards
• Three rotations about these axes:
– ROLL about the x-axis, positive right turning
– PITCH about the y-axis, positive right turning
– YAW about the z-axis, positive right turning
The Impact Force Vectors
Heave, Sway, and Negative Surge
Impact Forces Just Aft of Bulkhead B
Impact Forces Alongside Bulkhead C
Resultant force shown
acting perpendicular to
side plating in bilge
area.
For resultant contact
force vector shown,
heave component is
about 1.7 times sway
component.
The resultant force of impacting ice must be on a line that passes over the Center
of Gravity longitudinal axis (+) to cause the ship to heel to port. A sideswipe only
impact ~25 ft below the waterline would produce a heel to starboard.
Calculating Maximum Impact Forces Due To Side Impact Component
Contacting an Immovable, Smooth, Unbreakable Object
[Ref: S. Zhang,
"The Mechanics
of Ship
Collisions," Dept.
of Naval
Architecture and
Offshore
Engineering,
Tech. University
of Denmark,
1999.]
Calculation Assumptions
• Approach speed 38 ft/s (22.5 knots); Heading 0°
• Impact at t = 22.5 sec after "Hard-starboard" order
• Speed at impact 33 ft/sec; Heading -11°
• Angle of impact relative to centerline  = 12°
• Titanic's displacement 14 Apr = 48,300 tons
• Impact kinetic energy = 1,830,000,000 ft-lbs
• Point of max impact force taken abeam bulkhead B
• Center of gravity (CG) of ship taken at amidships
• Coefficient of friction steel-on-ice  0.03; set to 0
• Coefficient of restitution  0 (hull deformation only)
• Mass of iceberg  
Calculation Results
• Energy loss from collision = 27,530,000 ft-lbs
• Percent of energy lost = 1.5%
• Impact impulse = 8,100,000 lbs-sec  3,600 ton-sec
• Average sway force over 6 sec = 600 tons*
• Added rotational velocity imparted = 0.93° per sec
• Velocity of ship after collision = 32.3 ft/sec
• Sway velocity after collision = 1.3 ft/sec
• Center of percussion (CP) ~ 569 ft aft of bow
* Average force = impulse/time; peak forces can be much
greater. Highest forces probably across Holds 1, 2, and 3.
Model For Side Pressure Vs. Time
Assume side component contact with berg over area of 8 ft X 40 ft = 320 sq-ft.
Force impulse is 3600 ton-sec; Pressure impulse = 11.25 ton-sec/sq-ft
Assume a Rayleigh contact distribution over time with
peak force at t=2 sec.
Sway Force Vs. Time
1200
Pressure = Force/320 sq-ft
Peak sway force = 1092 tons
Peak sway pressure = 1092/320 = 3.4 tons/sq-ft
Force (tons)
1000
Sway Force = 3600*t/4*exp{-1/2*t2/4} tons
800
600
400
200
0
0
1
2
3
4
tim e (sec)
5
6
7
Estimating How Far She Heeled to Port
impulse analysis considering side
During Contact From
impact only, we found an average sway
component ~ 600 tons. To cause
observed heel to port, heave component
was shown to be ~1.7 times sway near
bulkhead C. Assuming resultant force as
shown, moment arm L  4 ft. Heel angle
would be given by formula shown below.
moment arm
L  4 ft
M
waterline
G
32.25'
F=1180 tons
resultant
1020 tons
heave
600 tons
sway
sin  =
Fx L
Disp. x GM
=
35.4'
38'
4/12 displacement = 48,300 tons (B&H)
4/12 draft = 32' 3'' (B&H)
GM = 2.63' (B&H)
sway component = 600 tons average over 6 seconds
heave  1.7 sway = 1020 tons
Resultant force F = 1180 tons  (sqrt [600^2 + 1020^2])
1180 x 4
= 0.037
48300 x 2.63

  2°
Underwater Contact — Sideswipe or Grounding?
Some Observations
•
A pure sideswipe (sway component force) would cause the
ship to heel to starboard, not to port, during the allision.
•
A pure grounding (heave component force) just along the
bottom of the hull would not likely produce what was
observed in the forward boiler rooms as the ship's double
bottom extended around the turn of the bilge in those spaces.
The most probable contact appears to be an allision
along the bilge area on the forward starboard side of the
ship producing heave, sway and slight negative surge
components to the forces of impact.
+
-
+
- +
CONTINUED IN PART 2