|Underwater Survey Guidance (NVIC 1-89)|
Subj: Underwater Survey Guidance
- PURPOSE. The purpose of this Circular is
to provide vessel owners and operators, underwater survey diving contractors,
and other interested persons guidance for conducting underwater surveys.
It addresses both the application process, the advance planning necessary,
and the procedures to be followed during an underwater survey.
- BACKGROUND. In December 1980, the Coast
Guard published the final report of a research project entitled "1980 Underwater
Technology Survey for Extension of Time Between Drydockings" (available
through the National Technical Information Service (NTIS), Springfield,
VA 22161, Report ADA 101-131). The report indicates that current technology,
properly applied with additional administrative and operational controls,
can provide a satisfactory means of inspecting the underwater bodies of
vessels without their being hauled out. Underwater examinations using video
equipment have been accepted on occasion by the Coast Guard as a means
of verifying the continuing acceptability of the structure of large mobile
offshore drilling units (MODU's) since 1969. Since publication of 46 CFR
107 in 1978, underwater examinations for column-stabilized and self-elevating
MODU's have been allowed by regulation. In 1982 an experimental underwater
examination program for ships was initiated and in 1983 a separate underwater
survey program for the Military Sealift Command's Near Term Propositioning
Force was established. These programs provided the basis for including
underwater surveys in the 1988 revision of the drydock and tailshaft regulations,
46 CFR 31.10-21(d), 91.40-3(d), and 189.40-3(d). These regulations provide
the option of alternating drydock examinations with underwater surveys
to owners and operators of tank vessels, cargo and miscellaneous vessels,
and oceanographic research vessels that are less than 15 years of age.
46 CFR 31.10-21(e), 91.40-3(e), and 189.40-3(e) also permit continued
participation in the underwater survey program for vessels 15 years of
age and older. Vessels older than 15 years of age which have not previously
participated in the underwater survey program are ineligible.
- Underwater surveys are optional. The regulations
permit owners/operators to alternate drydockings with underwater surveys.
For instance, a salt water service vessel that would normally be drydocked
at years 2.5, 5, 7.5, 10, 12.5, and 15 could conduct alternate underwater
surveys instead of drydocking at years 2.5, 7.5, and 12.5.
- Enclosure (1) is a guide for the underwater survey
- U.S. vessel owners and operators are encouraged
to use the guidance in enclosure (1) when applying for and planning an
- Underwater survey diving contractors are encouraged
to use the guidance in enclosure (1) when preparing to conduct an underwater
Rear Admiral, U.S. Coast Guard
Chief, Office of Marine Safety
Security and Environmental Protection
Encl: (1) Underwater Survey Guidance
Underwater Survey Guidance
- Entry Into Underwater Survey Program.
- Pre-Survey Drydocking. An owner who desires
to enter his vessel into the Underwater Survey Program must first drydock
the vessel. The purpose of this drydocking is to conduct a preliminary
survey of the hull to evaluate its condition and the feasibility of conducting
an underwater survey. This survey and the video discussed below will be
used as a reference for the first underwater survey once the vessel has
been approved for the underwater survey program.
- Hull Markings. During the pre-survey drydocking,
a means must be provided whereby the location of the diver relative to
the hull can be determined with sufficient accuracy to locate specific
points on the underwater body. This may entail a weld bead grid system
on the hull, a contrasting color coating system, a movable grid an acoustic
"pinger" locating system, or any other arrangement that is satisfactory
to the OCMI (Officer in Charge, Marine Inspection). Hull markings, or "targets",
every 100 feet, at the keel, below the turn of the bilge, and below the
water line are recommended. Consideration should be given to the possibility
that bottom coatings alone may wear off over time.
- Sea Chests. Hinged gratings must be installed
on all sea chests to allow divers access into each sea chest to inspect
the external sides of through hull connections and sea valves.
- Reference Video. Once all hull markings
and preparations have been made, a video tape with audio commentary should
be made of all external areas of the underwater hull, including rudder,
propeller(s), tailshaft(s), hull protective system, and all other attached
appurtenances. The video should clearly show the hull reference system,
required by 46 CFR 31.l0-21(d)(3), 91.40-3(d)(3), and 189.40-3(d)(3), which
will be used to determine the diver location relative to the hull.
- Applications for Underwater Surveys Instead
of Alternate Drydock Examinations.
- Applications for underwater surveys, as required
by 46 CFR 31.10-21, 91.40-3, and 189.40-3, should be submitted at least
90 days before the requested survey to the OCMI who will conduct the
underwater survey. The OCMI who issued the vessel's Certificate of Inspection
should also be notified that an underwater survey application has been
filed. The information required to be included in applications for underwater
surveys is specified in 46 CFR 31.10-21(d), 91.40-3(d), and 189.40-3(d).
To ensure that this information is presented in adequate detail, the following
specific items should be addressed:
- The identity of the diving contractor.
- The number of divers to be employed, type of
diving equipment to be used, and their underwater nondestructive testing
(NDT) and damage repair capabilities.
- A copy of the diving operations manual required
by 46 CER 197.420.
- The means of waterborne diver support.
- The means of taking rudder bearing clearances.
- The means of blanking sea chests for removal
of sea valves, if blanks are to be used. Also include their specifications
(i.e., thickness, material, PSI test pressure, etc.).
- A letter signed by the vessel's master, chief
engineer, or the person in charge, stating the general overall condition
of the vessel, level of maintenance, any known or suspected damage, cleanliness
of the underwater body, and the anticipated draft of the vessel at the
time of the survey.
- The number of additional or vessel personnel
who will be available to assist the dive team and Coast Guard marine inspector
in conducting the underwater survey.
- The anticipated duration of the underwater survey.
Experience indicates that at least 5-10 days should be allowed.
- The method by which and the extent to which
the hull will be cleaned.
- Whether or not an Internal Structural Examination,
Cargo Tank Internal Examination, and Integral Fuel Oil Tank exams as required
by 46 CFR 31.10-21, 91.40-3, and 189.40-3 will be conducted concurrently
with the underwater survey.
- Plans or drawings showing the external details
of the hull below the sheer strake, including the following items together
with a plan showing their location:
- all shell openings;
- all docking plugs;
- bilge keels;
- welded seams and butts;
- anodes, including methods of attachment;
- reference points; and
- watertight and oiltight bulkheads.
- Decisions of acceptability will be based on the
condition of the vessel, the hull protection system and the procedures
that will be followed for the performing of the underwater survey. Additionally,
the decision of acceptability will, in most cases, require an on-site evaluation
of the vessel by the cognizant OCMI. Previously, many items noted during
other inspections that required repairs were delayed until drydocking.
Now these same items may be required to be repaired earlier due to the
longer interval until actual drydocking or further delayed due to the impracticability
of accomplishing them at a place outside of a drydock facility. Accordingly,
during the on-site survey, particular attention will be paid to above the
gunwhale" conditions and outstanding requirements.
- Whenever more than just the underwater survey
is to be conducted, e.g., cargo tank internal or internal structural examinations,
an NFPA (National Fire Protection Association) certified marine chemist
should be available for initial tank gas-free certification, as required
by 46 CFR 35.01-1, 91.50-1, and 189.50-1. A competent person should also
be aboard for daily testing once the spaces have been certified "safe for
- Applications for Continued Participation in
the Underwater Survey Program by Vessels 15 Years of Age and Older.
As required by 46 CFR 31.10-21(e), 91.40-3(e), and 189.40-3(e), the request
to continue in the underwater survey program for those vessels which will
be 15 years of age or older at the time of the next underwater survey should
be submitted to Commandant (C-MVI) via the cognizant OCMI at least 90
days before the drydocking preceding the underwater survey. This advance
notice, which would be 3 to 5 years in advance of the requested
underwater survey, is intended to ensure that a thorough assessment of
the vessel is made during the drydocking preceding the underwater survey,
with an eye toward the vessel's suitability to go twice the drydock interval
between actual haul outs. Additionally, it will ensure that a complete
set of suitable hull gaugings is taken (see 46 CFR 31.l0-21(e)(2), 91.40-3(e)(2),
and 189.40-3(e)(2)). A complete set of hull gaugings is considered to be
all of the gaugings deemed necessary by the OCMI to determine the condition
of that particular vessel's hull. They should include as a minimumgaugings
taken around two or more complete transverse sections of the hull. Plate
gaugings of one or more strakes in the wind and water area, of additional
transverse belts, or of questionable areas such as those with heavy pitting
or fractures, may also be required. The results of the drydock examination
and the hull gaugings will be submitted by the OCMI to Commandant (C-MVI)
for final determination of whether the vessel may remain in the underwater
- Preparatory Meeting. A shipowner's representative
and a member of the diving team should conduct a preparatory meeting with
the Coast Guard inspector prior to the underwater survey to discuss the
details of the survey. In the case of overseas surveys, every effort should
be made to hold this meeting before the inspector proceeds overseas. At
this meeting, the duration of the survey, the site selection, the diver's
equipment, personnel and operation, hull cleanliness and preparation, extent
of internal examinations, route of the survey along the vessel's bottom,
and the overall conduct of the survey should be discussed. In addition,
the inspector will be able to advise the shipowner's representative and
the diver of all the items the inspector intends to inspect during the
underwater survey. Additional items may need to be surveyed depending upon
the actual conditions found aboard the ship during the survey.
- Conducting the Survey. The following guidelines
have been developed based upon Coast Guard underwater survey experience,
the NTIS report, and the American Bureau of Shipping (ABS) Guide for Underwater
Inspections in Lieu of Drydocking Survey, 1975.
- General. As a minimum, an underwater survey
will include a general examination of the hull plating and a detailed examination
of all critical welds, propeller, rudder, other hull appurtenances, sea
chests, and sea valves. Detailed examination of other areas will be conducted
as considered necessary by the inspector. It must be stressed that the
underwater survey program is an option that the ship's owners/operators
have elected to use. Responsibility for the management of the vessel, its
personnel, and maintenance of necessary safety and service systems remains
at all times with the master and his representatives.
- Duration of the Underwater Survey. The
underwater survey should take as long as the inspector considers necessary
to ensure that the ship is in a safe condition to continue until the next
drydock examination (up to 3 years for salt water service and 5 service).
Previous experience indicates that at least 5 days should be allowed to
conduct the underwater survey. However, if problems develop or repairs
become necessary, more time will be required. Initial estimates of the
duration of the underwater survey should be proposed by the owner in the
application and either refined or confirmed during the preparatory meeting.
- Site Selection. The location 6f the underwater
survey is of the utmost importance for two major reasons. First, the site
must be in an area with sufficient water depth under the keel and sufficient
clearance adjacent to both sides of the vessel to allow the diver to safely
survey the entire underwater hull of the ship, without concern for the
presence of hostile sea life or high current velocities. Second, the site
must have good underwater visibility. Conducting an underwater survey in
poor visibility could adversely affect the intent of the program (equivalency
to a drydock examination) and the safety of the ship. Water turbidity (clarity)
is a particularly subjective item, and the decision of acceptability will
be based primarily on the clarity of the television monitor presentation.
If the inspector feels that better visibility is required, the shipowner
will be given the option of either moving the ship to a location with better
visibility or drydocking the ship.
- Additional Personnel. Current trends in
automation and reduced staffing may result in a situation where a vessel's
normal complement will not provide a sufficient number of personnel to
assist in the inspection process and maintain the shipboard watch. Additional
personnel may be needed to act as line handlers to support the dive boat,
to position a movable grid if used, to pull sea valves, etc. Consideration
should be given to crew watchstanding responsibilities when evaluating
the need for additional personnel.
- Divers, Diving Equipment, and Operations.
The underwater survey should not be conducted unless the inspector is satisfied
that the equipment and procedures being used by the divers will provide
a safe and meaningful examination of the ship. Safety must be foremost
on the minds of all those working together on the actual diving operation.
While matters in this regard are best left to the experienced, professional
individuals normally found conducting this type of work, everyone involved
in the survey should be alert to these needs and ensure that any requirements
regarding this inspection can be safely accomplished. As required
by 46 CFR 197.202 commercial diving operations taking place from vessels
required to have Certificates of Inspection issued by the Coast Guard,
regardless of geographical location, must comply with the provisions of
46 CFR Part 197 Subpart B - Commercial Diving Operations.
- Acceptability Of Diving Personnel and Equipment.
A professional commercial diving firm should be employed by the owner.
While specific approval is not required by the Coast Guard, a subjective
evaluation by the OGMI or the attending inspector will be conducted. Such
an evaluation may consider:
- Prior experience or training;
- Qualifications of dive team members in photography,
nondestructive testing (NDT), underwater damage repair, and other training
- The type, quality, and condition of equipment
to be used, i.e., a color monitor and color tape video recording system
is required along with two way recorded audio between the diver and the
inspector. A still underwater photographic capability should also be available;
- The degree of professional approach/attitude,
as evidenced by an organized dive plan, personnel assignments, standbys
and backups, compliance with appropriate safety regulations (Coast Guard,
Occupational Safety and Health Administration (OSHA), various states),
- Hull Preparation. The underwater survey
should not begin until the inspector is satisfied that all areas of the
hull to be inspected, including sea chests and sea valves, have been cleaned
to allow for a meaningful examination. The method of cleaning is left to
the discretion of the vessel owner. Water blasting of welds is discouraged,
unless a particular problem is anticipated, because removal of paint and
coatings subjects welds to unnecessary corrosion and pitting. The reference
video taken at the pre-survey drydocking should be used to familiarize
all involved personnel with the layout of the hull markings and overall
condition of the hull at the time the recording was made. The internal
examination (opening up) of sea valves may require diver installation of
custom prefabricated blanks or watertight boxes on through hull fittings.
Each hull opening to be blanked or plugged should be permanently marked
or identified on the hull. This will simplify verification that blanks
are inserted and removed from the correct hull openings. The ship should
be at, or as close as possible to, its light draft.
- Sea Valves.
- The preparation of the sea valves for inspection
during an underwater exam is most critical, as it will affect the watertight
integrity of the hull and the ability to keep essential machinery in operation.
Prior to commencing the examination of sea valves, the vessel's personnel
should develop and provide a detailed procedure which at a minimum includes
- The number, type, size, and method of operating
the sea valves to be opened.
- The disabling of automation features which might
affect the sea valves being examined.
- Method of installing blanks/plugs for sea chests/valves.
- The sequence of valves to be blanked/opened should
ensure that vital cooling systems, essential electrical service, and bilge
and fire pumping capabilities are maintained.(e) Closure of watertight
- An emergency procedures plan.
- Means of communication between the bridge, dive
team and engineroom (direct communications via sound powered phones are
- Removing and examining sea valves while a vessel
is afloat and while some portion of the machinery plant remains in operation
is. a situation not generally experienced by shipboard personnel. Of necessity,
all involved personnel should maintain the highest sensitivity to problems
which may start out small but could lead to more serious matters. Intentionally
disabling some systems is not a typical operation and should be carefully
controlled by the ship's personnel. Sometimes the failure of internal safeguards
or other construction features can lead to pressure in piping systems thought
to be slack. This condition can lead to lengthy delays while the cause
is located and corrected. Points to consider are:
- Interconnected sea chest vents that meet below
the water line will subject both sea chests to sea pressure unless both
sea chests are blanked simultaneously.
- Failure of check valves can pressurize secured
systems. This would most likely occur in crossovers between main and auxiliary
fire pump lines, main and auxiliary cooling systems and crossovers to the
sanitary Systems from any other salt water system.
- Temporary "jumpers" installed to keep essential
systems on line may defeat the designed system isolation.
- Pressurizing auxiliary and sanitary systems with
full fire main pressure can damage equipment designed for low pressure
- Bearing Clearances. Readings of the propulsion
shaft bearing and rudder shaft bearing clearance should be taken. These
readings should be acceptable to the inspector as accurate and reliable.
Otherwise, drydocking the ship may be necessary. Clearances should be compared
with those obtained during the last examination and meet the standards
set in 46 CFR 61.20-23.
- Internal Structural Examination, Cargo Tank
Internal Examination, and Fuel Oil Tank Examination. These exams are
required by 46 CFR 31.10.21, 91.40-3, and 189.40-3 and include an examination
of the vessel's main strength members, including major internal framing,
hull plating, voids, and ballast tanks. In most situations, the internal
structural examination should be conducted before, or at the same time,
as the underwater survey. The results of the internal structural examination
should be used to identify those areas where a problem exists or is suspect.
These areas should be given special emphasis when conducting the external
- Repairs and Deficiencies. Any required
repairs should be performed to the satisfaction of the inspector. Depending
upon the magnitude of the repair or the number of repairs necessary, this
may result in an unsatisfactory examination and require drydocking of the
ship. Deficiencies that are not repaired, or are not considered severe
enough to require repair, will be evaluated in conjunction with the overall
results of the underwater survey in determining whether the ship should
be allowed to operate a full interval until the next drydocking. If there
is doubt as to whether a ship is in a sufficiently safe condition to operate
a full interval until the next drydocking (up to 3 years for salt water
service and 5 years for fresh water service), a requirement to drydock
the ship may be issued.
- Underwater Inspection Techniques And Equipment.
- General. The attending inspector will
generally be limited to viewing the television (TV) monitor, reviewing
video tapes, talking with the diver, observing NDT procedures, reviewing
any still photos, and reading the diver's survey report. This method of
survey does not generally lend itself to the flexibility and "hands-on"
aspects marine inspectors have come to know at normal haul outs. Nevertheless,
there are a number of things that can and should be prepared for. The diving
operation will normally be a surface supplied air dive that includes the
diver, a tender watching the diver's umbilical, a standby diver (usually
the tender), and the diving supervisor. Communications with the diver should
be via hardwire. The TV monitor should be located close to the diving supervisor's
position to facilitate simultaneous viewing of the TV monitor and communication
with the diver.
- Diver's Observations. The diver's visual
findings and commentary can be very beneficial. A knowledgeable inspection
diver can provide greatly enhancing detail and description to the TV monitor.
For example, wiping off sea growth to clear a picture of the weld or carrying
a short ruler or a marked diving knife to give dimensions can be helpful
to topside viewers. On the other hand, the camera used by the diver provides
a small field of view. The view can be affected by water clarity, the diver's
exhaust bubbles, the diver's motion and speed of advance, glare from the
diver's light as well as the amount of available light, etc. The diver's
comments on the overall condition of the hull regarding sea growth, damages,
and the coating system may prove to be helpful, but the inspector will
maintain control of the inspection by requiring the diver to proceed at
such a pace so that there is good visual acuity of the section of the hull
being photographed. The inspector may also have to direct the diver to
adjust the attitude of the camera to reduce glare or to bring an item more
into focus. The measure of reliance upon such information is left to the
judgment of the inspector at the time of the inspection and, ultimately,
to the OCMI.
- Monitor System. A color TV system should
be used. A color bar or test slate should be available to allow proper
adjustment of the picture for maximum efficiency and clarity. This includes
consideration for a compatible lighting system (type of light, candlepower,
etc.). The monitor presentation should be satisfactory to the inspector/OCMI.
It should concentrate on hull appurtenances (propellers, rudders, bilge
keels, sea chests, etc.) as well as any areas of damage. Although it may
not be necessary to cover every inch of every weld on the underwater body,
the attending inspector/OCMI should be satisfied as to their satisfactory
condition. [NOTE: The owner should provide a copy of the audiovisual tape
and the written report by the diving company to the OCMI.]
- Photography. Still photography, particularly
35mm, provides generally improved detail as compared to TV pictures. This
is particularly useful in specific or localized applications such as damage
or deformation. Its use is highly recommended when questionable areas are
found on a hull.
- NDT Procedures. These may consist of the
diver's visual examination, magnetic particle inspection, or ultrasonic
testing. For crack detection or. help in determining the extent of cracks,
magnetic particle methods are available. For thickness gauging, ultrasonic
testing is recommended. In any case, operators should be appropriately
qualified and qualifications should be verified. Equipment calibration
is likewise necessary. It is recommended that NDT personnel be ASNT Level
II qualified (American Society for Nondestructive Testing).
- Acceptable Underwater Repairs. Limited
underwater repairs are possible, utilizing newly developed techniques or
materials. Some applications of welding, both wet and dry, below the water's
surface are possible. Presently, any underwater weld should be considered
a temporary repair, subject to reevaluation at subsequent inspections and
haul outs. Fabrication and quality assurance standards for underwater welding
can be found in the American Welding Society's, "Specifications for Underwater
- Evaluating Results of the Survey. The not
prevent the underwater survey from satisfaction of the inspector. If the
with the results of the survey, credit ship's operating schedule should
being conducted to the complete OCMI is not completely satisfied will not
be given for the survey.