UNDER WATER SURVEY OF VESSELS (All about UWILD / IWS /UWS/ In Water Survey Notations)


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The inspection of vessel in the presence of attending surveyor of a recognised organisation (classification society), whether scheduled or unscheduled, for accessing the condition of hull, it’s paint, markings and it’s fittings below the waterline and some part of exposed area of hull and it’s fittings which frequently goes under water, is called underwater survey.

Different Classification Societies provide different notations for under water Survey in the class certificates

Following are examples of few Notations related to under water survey provided by different classification societies

  • UWILD – American Bureau of Shipping (ABS)
  • IWS – Class NK
  • UWS – Lloyd’s Register (LR)
  • IN WATER SURVEY – Indian register of shipping (IRS)
  • INWATERSURVEY – Bureau Veritas (BV)
  • Bottom-In water Survey – RINA


A scheduled under water survey which is often termed as “Under Water Inspection In lieu of Drydocking(UWILD) or In Water Survey (IWS) is generally a part of intermediate survey. Following to be satisfied for vessel to go for inspection under UWILD/IWS.

  1. Vessel must have an approved UWILD or IWS plan also called as “Booklet for In water survey”
  2. Vessel must have the maintained UWILD or IWS notation in it’s certificate of compliance.

Unscheduled Under water inspection:

  1. For measuring hull fouling. In some countries like New Zealand and Australia, hull fouling is a serious issue. Vessel visiting these countries must take necessary precaution in regard of hull fouling. Hence under water inspection and cleaning becomes necessary if vessel is visiting the above-mentioned ports.
  1. Vessel Performance Issues: If vessel is facing Speed-fuel Consumption issues, underwater inspection and cleaning should be carried out.
  1. Damage/repair/accident survey for accessing the extent and severity of damage. 

How to get UWILD/IWS Notation?

  1. All requests for Underwater Inspection in Lieu of Drydocking Survey are to be forwarded by owner/operator/shipbuilding yard to the applicable Office of classification society for review and authorization.
  1. The concerned class will provide the guidelines for getting the UWILD/IWS notation.
  1. An initial survey is planned for the vessel, vsl notified, survey fixed after paying the survey fee.
  1. All arrangements made as per the guidelines provided by class. Plans showing the following items are to be submitted to the attending Surveyor, together with the proposed inspection procedures for review, well in advance of the inspection.
    • Location of bottom shell seams and butts (Shell Expansion), including any doublers, straps, bottom plugs, appendages and all underwater openings.
    • Hull markings or other means to orient the diver and identifying photographs, which entail specific areas of plating, (e.g., locations of bulkheads or tanks) sea suction and discharge openings, propeller blades and rudder surfaces. Such preparations may include a weld bead grid system on the hull, a contrasting colour coating system, a movable grid, an acoustic locating system, or any other arrangement that is satisfactory to the Surveyor.
    • Reference data and instructions to the diver for any necessary underwater operations such as means of access to sea chests to inspect the external side of hull connections and sea values, to rudder bearings to determine clearances of rudder bearings or to propeller shaft strut and stern bearings.
    • Most recent gauging and it’s report from last Special Periodical Survey and the as-built scantlings for the underwater body.
  1. Initial survey of vessel carried out in following manner
    • New vessel survey is carried out during construction period.
    • Existing vessel survey is carried out of water, that is in Dry dock.
  1. The results of initial survey are documented and submitted for further review.
  1. After a satisfactory review and approval of the UWILD plan the vessel is issued a certificate of compliance or included in the class notation. The UWILD notation is mentioned in the section “Additional Notations” of this certificate.


What are the limitations of UWILD/IWS?

  1. UWILD/IWS is applicable if Vessel has no outstanding recommendations for hull and it’s fittings.
  1. If damage affecting the fitness of the vessel is recorded during the course of the survey, the vessel has to be docked to carry out the necessary repairs.
  1. For vessels 15 years of age or over and subject to the Enhanced Survey Program (ESP), Underwater Inspections in Lieu of Drydocking (UWILD/IWS) are not permitted as an alternate to Drydocking Surveys.
  1. Non-ESP vessels 15 years of age or over applying to maintain UWILD/IWS notation are subject to special consideration based on the following review and examination before being permitted to have underwater inspection
  • Review of vessel’s records to ensure that no unusual repairs have been required/made
  • Internal examination of representative tanks and cargo holds
  1. Underwater Inspection In Lieu of Drydocking Survey (UWILD/IWS) may be restricted or limited where there is record or indication of abnormal deterioration, existing recommendation, or damage to underwater body, rudder, or propeller.
  1. Flag Administrations may have specific regulations for Underwater Surveys in Lieu of Drydocking, including requirements for enrolment, hull markings, extent of visibility and procedures for older vessels.

A Successfully completed Underwater survey is the alternative to intermediate Drydocking survey which can be held at 2.5th year, 7.5th year and 12.5th year intervals hence an ESP vessel such as Bulk carriers can take up minimum 3 under water surveys till the age of 15 years and after that no more underwater survey in lieu of drydocking. A non-ESP vessel (vessel other than Oil tanker, Bulk carriers, Combination carriers and chemical tankers) after 15 years of age can be further allowed to opt for in water survey in lieu of drydocking if condition of vessel is sound and no unusual repair has been carried out previously.


What are the areas covered in the under-water survey? 

Hull part:

  • Condition of random area of hull plating which includes condition of paint, any sign of damage, dent and amount of corrosion and fouling
  • Condition of Bulbous bow
  • Condition of bilge keel
  • Condition of rudder trunk area.
  • Condition of plugs securing and their identification marks punched over them and to be provided on hull in the form of weld beads
  • Echo sounder and speed log fittings no damage.
  • Sea suctions, gratings, their numbers in full weld beads and painted and amount of fouling
  • Overboard valves openings their numbers in full weld beads and painted.
  • Various hull markings like tug push marks, bulbous bow marks painted.
  • Condition of Stern Frame any damage, amount of fouling.
  • Condition of anodes and it’s securing, percentage of consumption.
  • Condition of other ship specific underwater fitting such as thrusters, stabilizers etc.


  • Condition of propeller blades for any damage, fouling etc
  • Condition of propeller boss and fins if applicable.
  • Wear down of stern bush (propeller drop): Wear down/Poker gauge reading
  • Condition of rope guard and anything entangled with propeller
  • Condition of stern frame


  • Condition of pintle and neck bearings, clearance of bearings checked by surveyor where ever possible depending upon the arrangement of the rudder stock.
  • Condition of rudder plating 

What are the key features to be incorporated in to vessel’s design in order to get UWILD notation and carryout under water inspection there after? 

  1. Rope guards to be provided an access hole and a diver’s grip on top and bottom. Accesses holes to be aligned with gauge position.


2. Blade Positions on propeller and boss to be marked so that propeller is kept locked in the same position each time the survey carried out.


3. Rudder lower pintle to be fitted with a removable Box and Inspection Hole to facilitate the measurement of lower pintle clearances.


4. Identification marks, all marks to be welding beads and painted. Below shows sea chest’s and discharge over board’s identification marks for reference.

5. Hinged sea chest Grids for ensuring the diver that sea suction openings are clear and clean if necessary


6. Bottom plugs of to be fitted flush with shell on each water ballast tank in double bottom, peak tanks, fuel oil tanks in double bottom, Bilge separated oil tank, fuel oil overflow tank, bilge tank and stern tube cooling water tank.

7. Each bottom Plug to be punched marked and welding bead on shell plate to be provided for identification purpose.


How to Go ahead with Under water Survey 


  1. Ship schedule closely monitored both by vessel and office between the window period of intermediate survey of vessel.
  2. To decide on the vessel schedule when it is in light condition. Where possible, the underwater examination should be carried out in protected waters, preferably with weak tidal streams and currents and with the vessel at light draft.
  3. Office sends the formal survey request to the class. Class suggests the availability as per tentative vessel’s schedule along with the quotation.
  4. Office reviews the quotation and confirm the Survey request.
  5. A class approved Diving company is booked for the scheduled date, the diving company has to employ fully qualified divers approved by class. Class may request to arrange a cleaning of hull prior undertaking the survey for having a meaningful examination of the Hull.
  6. Office notifies vessel about the booking of class surveyor and Diver company.
  7. Vessel liaise with surveyor and diver company and keeps them update with latest vessel schedule.
  8. Necessary info is shared among vessel, attending surveyor and diver company for close coordination and better in water survey preparation.
  9. Master sends the port agent details to surveyor and diver company. Both surveyor and diver company directly liaise with agent for coming onboard. All necessary permission required from port control for diving operation is obtained by diving company with the help of port agent or any other local agent.
  10. Master informs port control, with assistance of the agent, and attain permission to carry out the diving operation for survey purpose.

Preparation for diving operation 

  1. Initial meeting comprising Master, chief engineer, diving team supervisor and attending class surveyor is done and scope of work discussed. The scope of work to be sufficient to include all items which would normally be examined if the vessel was on drydock.
  2. Plans containing Location of bottom shell seams and butts (Shell Expansion), including any doublers, straps, bottom plugs, appendages and all underwater openings discussed.
  3. Hull markings or other means to orient the diver and identifying photographs, which entail specific areas of plating, (e.g., locations of bulkheads or tanks) sea suction and discharge openings, propeller blades and rudder surfaces.
  4. Reference data and instructions to the diver for any necessary underwater operations such as means of access to sea chests to inspect the external side of hull connections and sea valves, to rudder bearings to determine clearances of rudder bearings or to propeller shaft strut and stern bearings.
  5. Most recent gauging and gauging report from last Special Periodical Survey and the as-built scantlings for the underwater body.
  6. A safety checklist to be followed which also help in preparations for carrying out diving operation safely. Please refer Appendix-A “CONTENTS OF A TYPICAL INWATER SURVEY REPORT” for check list.
  7. All arrangements made for carrying out diving operation safely and Means are provided to enable the Surveyor to accomplish visual inspection of area outside of the shell plating above the waterline and exposed portions of appendages (such as propeller, rudder and rudder bearings).

Commencement of diving operation:

  • Once everything is ready Diving Flag is raised, master informs port control about commencing diving operation. Commencement of diving operation is logged in to port log.
  • Underwater inspection begins by qualified divers under the surveillance of the attending Surveyor and one representative from vessel, preferably master or chief engineer.
  • A good two-way communication between the Surveyor and divers is to setup.

  • The vessel’s underwater body is to be sufficiently clean and the sea water is clear enough to permit meaningful examination and photography by the diver. “Sufficiently clean” is taken to mean that sections of the underwater body, including flat keel plating forward, amidships and aft, are cleaned to the extent that the Surveyor can determine the condition of the plating, the welding and the coating. Additional cleaning may be necessary. Overall or spot cleaning may be required at the discretion of the attending Surveyor.
  • An examination of the entire vessel below the waterline is to be carried out by a Class approved diver using closed-circuit television with two-way communication. The progress of the dive is to be monitored by the onboard Surveyor as required and is to be photographically documented along with videos. Items that must be recorded on the tape/photograph include but are not limited to:


  1. Time at which dive commences
  2. Point of commencement
  3. Time viewed
  4. Hull parts
    • Conditions of hull markings
    • Random areas of plating
    • All sea chests
    • All inlets and discharges

5. Rudder

    • Pintles

6. Propeller: Follow Appendix-B for detailed procedure

7. Time and point of completion of the dive


Completion of diving operation:

  • Port control is informed about completion of diving operation.
  • Time of completion to be recorded in port log.
  • The ship system which was locked or isolated for the safety reasons can be returned to normal.
  • The above examination is to be supplemented by the diver’s report describing and attesting to the conditions found. A copy of this report and pertinent photographs are to be submitted to the attending Surveyor. Copies are also to be retained onboard. Please refer Appendix-A “CONTENTS OF A TYPICAL INWATER SURVEY REPORT”

If no abnormality noted by attending surveyor, underwater inspection may be credited as an alternative of Drydocking Survey.

  • If the Underwater Inspection reveals damage or deterioration that requires further attention, the Surveyor may require that the vessel be drydocked in order to undertake a detailed survey and necessary repairs.


  • If by some reason the attending surveyor is not able to determine the condition because of dirty water, the diving operation may be suspended, class may grant extension till the next port.
  • An ESP Vessel above 15 years of age, seeking extension, an in-water survey is carried out which is only for postponement purpose and docking is not credited 


Ashish Goyal

Chief Eng. Dockendale Ship Management

Email: ashishgoyal@marinetecs.com



Below are following appendixes for references.


  • Appendix-D:







  • Class NK Rules For IWS
  • Section 1. Of Rules for Classifications: Ship – DNVGL-RU-SHIP-Pt6Ch9. Edition October 2015
  • Bureau Veritas Classification e-rules on In-water Survey (INWATERSURVEY), Ch1, Sec2, [6.14.3]
  • In water Survey Booklet of Different vessels
  • Consultation with Cpt. Stetson Jude Rebeiro, Master with Dockendale Ship Mgmt. (India) Pvt. Ltd.