Coast Guard issues alert on stability letters, shaft-seal assembly

The following is a marine safety alert issued by the U.S. Coast Guard:
 
LESSONS LEARNED FROM TWO SEPARATE MARINE CASUALTIES

* Stability Requirements
* Assembly of Shaft Seals

TOWING VESSEL STABILITY REQUIREMENTS

This document presents lessons learned during a casualty investigation. It
provides useful information for marine inspection and investigation
personnel in addition to owners and operators of Towing Vessels and other
vessels having similar characteristics.

Stability Requirements

Several years ago an ocean going towing vessel sank forty miles off the
Eastern seaboard during inclement weather involving with 40-50 knot winds
and 15-20 foot seas. At the time of the casualty the towing vessel was
towing a loaded barge containing about 175,000 barrels of oil. Prior to the
casualty, the towing vessel had no material failures or deficiencies. Its
systems, equipment, and components were all operating as designed. The
causal factors of the casualty consisted of multiple human errors which had
disastrous results when the vessel was experiencing extreme environmental
conditions. Several senior crewmembers onboard the vessel erred by
operating the vessel without regard for the vessel’s stability letter. They
were non-compliant with the letter and also demonstrated a general lack of
knowledge of the letter’s content, specifically the “Operating Restrictions”
section.

Stability letters apply to a vessel at all times and are continuously in
effect. Although vessel stability letters are addressed to the master, all
of the deck officers are responsible for stability issues. Vessel engineers
are also responsible to ensure that the master and other deck officers are
aware non-compliance issues that take place within the engine room. The
letter’s “Operating Restrictions” may state that certain restrictions only
apply when the vessel is underway. There are standard phrases that are on
every stability letter. The ones that applied to this casualty follow:

1) TANKS: No more than one centerline tank or P/S tank pair of potable
water, lube oil, dirty oil and ballast water and two P/S pair of fuel oil
tanks may be partially filled at one time.

2) TANKS: Any cross-connections between port and starboard tank pairs shall
be kept closed at all times when underway.

3) LIST: You should make every effort to determine the cause of any list of
the vessel before taking corrective action.

In this instance the master allowed other deck officers and engineers to
initiate ballast operations to correct minor lists. He never directed
anyone to determine the cause of the lists. The engineers routinely left
fuel tanks cross-connected on the P/S tank pairs that were feeding the day
tank per standard company/industry-wide practice. In this specific incident
an additional set of P/S fuel oil tank pairs were also cross-connected.
These seemingly inconsequential practices and other improper ballasting
actions caused the vessel to develop a significant port list which initiated
a hydrostatic balancing condition. The practice occurred during a severe
storm thus exacerbating the negative effects.

Hydrostatic balancing is a condition that occurs when a vessel heels or
lists enough to cause fuel (or other tank fluids) from the higher tanks to
flow (through cross-connected valves) to the lower tanks, moving the center
of the fuel weight (or other fluid) off of the centerline and increasing
the heel angle. Fluids from the higher tank when cross connected with the
lower tank may actually “press up” the lower tank and cause fluid to flow
out of the lower tank’s vent(s).
In this particular case the vessel’s list continued to increase due to
hydrostatic balancing until additional flooding occurred through the stack
vents. The engine room eventually flooded sufficiently enough to cause the
vessel to sink.

The Coast Guard strongly reminds vessel owners and operators to ensure that
all deck officers and engineers are fully apprised of the vessel’s stability
letter requirements and that the vessel is operated in compliance with those
requirements at all times.

The full report of investigation for the TUG VALOUR sinking can be found at
http://marineinvestigations.us > Marine Casualty Reports> Other Narrative
Type Marine Casualty Reports.”

This document is provided for informational purposes only and does not
relieve any domestic or international safety, operational or material
requirement. Developed by the Headquarters Office of Investigations and
Analysis and the Investigations Division. Questions regarding the casualty
may be addressed to LCDR Charles Barbee, Charles.B.Barbee@uscg.mil .

++++++++++++++++++++++++++++++++++++++++++++++++++

Improper Assembly of Shaft Seals

This document presents lessons learned during a casualty investigation. It
provides useful information for marine inspection and investigation
personnel in addition to owners and operators of Towing Vessels and other
vessels having similar characteristics.

Recently a towing vessel nearly sank while conducting vessel assist
operations in San Juan harbor. A large volume of water flooded the engine
room when the vessel applied astern propulsion. Within a few minutes,
severe flooding filled the engine room with twelve feet of water.
Fortunately the Master was able to intentionally ground the vessel to avoid
sinking.

An investigation revealed that the water had entered through a gap between
the vessel’s shaft seal and its mounting flange. When the vessel applied
astern propulsion, the force of water was directed down the shaft towards
its seal thus dislodging it from the flanged mounting / mating surface. The
vessel had recently installed a Kobelco brand dry shaft seal during a yard
period. Installation required a new flanged mounting welded to the vessel
structure.

The mounting flange had been tapped for the use with M20 metric bolts.
During installation the seal was secured to its mounting flange with eight ¾
inch diameter (nominal size) bolts. The differences in the diameters of the
tapped hole for a ¾ inch bolt and a M20 bolt is quite small and the pitch of
the threads are very similar. Because of these similarities the use of a ¾
inch bolt into a 20M metric tapped hole may go unnoticed.

In this instance, the improperly fitting bolts eventually loosened and
allowed the seal assembly to separate substantially from the flange mounting
surface when astern propulsion was applied. Post casualty, the owner /
operator reinstalled the proper bolts and enhanced the installation with the
use of a locking device to prevent future loosening.

“Human error” likely resulted in the selection and installation of improper
bolts. Inadequate “situational awareness” may have contributed and failed to
provide the proper “defenses” to prevent the casualty. Careful and routine
machinery space rounds by competent persons and attention to critical areas
like shaft sealing arrangements may have detected the initial loosening of
the bolts and leakage occurring at the seal.

The Coast Guard strongly recommends that owner operators of vessels
utilizing Kobelco shaft seals or similar devices ensure that the proper
fasteners are used. Further, critical inspection of machinery should take
place anytime modifications are made and regular inspection of important
areas such as shaft seals, skin valves, sea chests and other hull
appurtenances should be part of a daily machinery space rounds onboard any
vessel.

This document is provided for informational purposes only and does not
relieve any domestic or international safety, operational or material
requirement. Developed by the Headquarters Office of Investigations and
Analysis and the Investigations Division, USCG Sector San Juan. Shaft seal
questions can be addressed to LT Sarah Geoffrion, Chief of Investigations at
Sarah.J.Geoffrion@uscg.mil. Other questions can be addressed to Mr. Ken
Olsen at Kenneth.W.Olsen@uscg.mil.

By Professional Mariner Staff