DRYDOCKING 101

SPECIAL DRYDOCKING SITUATIONS

There is wide variety of special situations that will inevitably develop when one is involved in drydocking ships over any reasonable period of time. The individual nature of ships and of ship repair requirements assures that these special circumstances will arise.

As the Dock Master has already learned, every drydocking is “special” in that it requires attentive, individual care in both planning and execution. The Dock Master will find that the special drydocking situations will tax his ingenuity, his capacity for original planning, and especially his knowledge of and ability to apply the basic principles that ensure the safe operation of a dry dock. This chapter is aimed toward provoking thought and questions about serious problems every Dock Master may have to face when handling these situations.

Damaged Ships

Much of the work of dry docks involves the repair of damaged ships. The drydocking of damaged ships is a challenging problem as each case is new and unique to itself. Problems arise relating to a ship’s hull form, hull strength, list, trim, stability, and the dry dock capabilities.

The docking of a damaged ship presents to the Dock Master his most challenging assignment:

  1. Each case of damage is different.
  2. Standard docking plans serve as a guide but may require modification.
  3. Standard ship weight distributions may be incorrect.
  4. Ship stability must be corrected for free surfaces and for inclined centerlines if the damage involves flooding.
  5. Ship hull structure may be both grossly distorted and weakened.
  6. The ship may be unable to enter the dry dock until divers clear away damaged side and/or bottom plating.

Ships with compartments open to the sea should be landed slowly, allowing flood water to drain from the ship as it is landed.

Flood water in holds, tanks and other compartments which have progressively flooded or have been flooded during fire fighting may not drain as a ship is drydocked. If damage control dewatering has not been effective, it may be advisable to have a diver open the compartment to the sea to allow the water to drain as the ship is landed.

Because of weakened ship hull girder strength, local weight concentrations in the ship may be abnormally concentrated on the dry dock. This can result in excessive block loading or loading on the dry dock. For this reason, it may be advisable to partially or totally dry dock the ship, affect an immediate hull girder strengthening, and then carefully redock the ship for a final repair.Damaged ships are often unstable. Wale shores are frequently used to provide the needed stability upon drydocking. Sideblocking and spur shores can be carefully fitted after the hull shape has been determined.

Often, the drydocking of a damaged ship is an emergency situation. Planning time is short and advance information is sketchy. The Dock Master must plan and improvise as the situation develops. This will call upon all his expertise and knowledge of the drydocking operation, and especially upon his ability to foresee contingencies.

Hull damage may result in changes in hull form calling for blocking arrangements substantially different from those of the standard Docking Plan. Diver inspection of the hull is important to survey the extent and nature of damage and to determine the location and extent of any protruding members that could interfere with entering the dry dock or landing on the blocks. After landing on the blocks, careful diver surveys should again be made to assure that the blocking conforms to the hull as planned, and that further adjustments and additional blocks are not required.

Hull damage may so weaken the hull that the ship’s overall longitudinal strength has been seriously impaired. In cases of very serious damage, it is sometimes necessary to consider the forward and after portions of the ship as separate sections and plan the simultaneous docking of the “separate” parts so as not to impose further load on the remaining structure.

In case of flooding, the stability of the ship may be impaired. A very careful stability analysis is required. If adequate stability is retained, landing the ship will dewater flooded compartments, reduce free surface effects, and will normally result in a lowering of the center of gravity.

Special Design Ships

Special design ships may have hull characteristics that pose unusual problems to the Dock Master. Each case requires careful and detailed study when it arises. Many naval hull forms with little or no flat bottom and a high dead rise require very high bilge blocking and are unusual in that sense.

Tugs and trawlers also present unusual forms. The operational requirements for both result in a design with a large screw and often a large designed drag. Like many naval ships, many of these ships have no flat bottom, high dead rise, and a very rapid rise of buttock lines aft; all of which lead to high blocking for their size. Many, especially among the trawlers, are fitted with a bar keel rather than a flat keel. This requires special consideration of the keel block design.

Hydrofoils and Surface Effect Ships literally fly over the water, supported not by buoyant forces but by hydrodynamics and aerodynamic forces. Major portions of the hull cannot handle concentrated local hull loads. Special blocking arrangements must be designed to support the craft. Particular care should be taken to follow the Docking Plans for these craft in all required details. For all very light scantling ships, including fast patrol boats, special care must be taken to avoid local structural damage from block loading.

Cycloidal Propellers, Special Oceanographic Facilities have unusual long structures protruding beneath the keel of the ship. Docking Plans for such ships call for unusually high blocking or may require the provision of a recess or pit under the special fitting. The drydocking is further complicated by the need for special planning to move the ship into place over the high blocking.

As ship design changes and advanced ship concepts are introduced, the Dock Master may be confronted with the need to dry dock ships with markedly different underwater forms. For example, the unusual hull features that may be encountered include:

  1. Extreme bulbous bows (on tanker classes).
  2. Extreme below keel bulbous bows or sonar domes.
  3. Hydrofoil craft.
  4. Surface effect ships.
  5. Ships with vertical axis propellers.
  6. Ocean exploring and research vessels.

In most cases, adequate Docking Plans are available. In the case of major, below keel level protuberances such as sonar domes, it has been found necessary in some cases to modify dry docks to permit handling of these ships.

In the case of hydrofoil craft and air cushion vehicles, the lightweight hull construction will require careful analysis. Blocking support can only be provided at points designed to absorb the block loading, or must be widely distributed to limit local loading and pressure.

In the case of hydrofoils, ships with vertical axis propellers and other ships with long, below keel line protuberances, very high blocking may be required. This presents the following problems:

  1. Structural stability of the high blocking must be assured. This is usually accomplished by cribbing.
  2. Adequate clearance between ship and blocks during drydocking and undocking must be assured.
  3. The stability of the ship/dry dock combination during docking and undocking must be checked (floating dry docks).

Since the center of gravity of the ship may be high, the situation may be more critical than that for the routine docking of normal hull forms.

In the case of hydrofoil ships, the beam of the ship in way of the foils is unusually large as compared to the beam of more normal hull forms having about the same displacement. This requires the use of a wide dry dock. In addition, dry dock loading concentrations require study. If the foils are non-retractable and the ship must be landed on the foils alone, the concentration of the load on the dry dock may be extremely high. Construction of special cradles to distribute this load and to partially support the ship by its hull is advisable. If work is to be done on the foils, then hull support is mandatory.

As mentioned above, damaged ships are special cases in the sense that the underwater hull form is unknown. Here, examination by divers can determine the arrangement of blocking that can best be used. At times, it has been found advantageous to bring the damaged ship into the dry dock and lower the water level so it is several feet below the ship’s keel. Divers can then use the dry dock as a working platform while they examine the hull and take the measurements needed to plan the block arrangement. The ship is then removed from the dry dock to erect the desired blocking.

Special Work in Dry Dock

Replacement of sonar domes, sensors, shafting, rudders and hull plates are a few examples of work which can call for repositioning of blocks or for unusually high blocking during a drydocking and may present unusual or unique problems to the Dock Master. The experienced Dock Master will carefully note the work planned and recognized and anticipate special needs.

Multiple Ship Dockings

To efficiently employ ship repair facilities multiple ship drydockings are commonly carried out. A multiple ship docking presents the Dock Master with all of the problems associated with the drydocking of each individual ship, plus the complications that are added because of the multiple ship operation. For each individual ship, all of the drydocking requirements previously discussed must be met. Some of the additional complications of multiple ship operations are discussed below.

Multiple ship dockings can be carried out using a variety of arrangements of ships within the dock basin. The arrangement selected by the Dock Master depends upon a number of factors. Among these are:

  1. Dry dock dimensions and ship dimensions
  2. Dry dock strength – Most dry docks are designed for keel block loading along the centerline, and at one or more off-center lines located above longitudinal bulkheads or side girders. The Dock Master must be familiar with the structural arrangement and the limitations of his dry dock with regard to points and magnitude of loading.
  3. Dry dock lifting capacity (floating dry docks) – When a multiple ship drydocking is planned with total lift near dry dock lifting capacity, the ships will have to be placed so that their combined center of gravity is close to the center of buoyancy of the dry dock when it is raised to its working freeboard. If not, ballast water must be retained in order to control dock list and trim, and adequate working freeboard of the pontoon may not be attainable. The “Differential Pumping,” explained in Chapter Two, discussed the concerns centering on overall dry dock strength. For sectional dry docks, this consideration combined with the requirements for differential pumping may serve as a bar to certain multi-ship drydockings. While the total lifting capacity of the dry dock may be adequate, drydocking stresses may generate an unacceptable weight distribution.
  4. Repair requirements – In many dry docks, rudder work and propeller work are most conveniently done with the stern of the ship near the end of the dock. This normally provides maximum working space unencumbered by the proximity of adjacent ships. This consideration, or other significant repair work requiring working space, may affect the placement of the ships in the dry dock.
  5. Repair schedules – It is possible in a dry dock, to drydock and undock one ship while a deeper draft ship remains firmly landed on the blocks. Such a maneuver obviously involves planning the placement of ships in the basin and must be planned and coordinated with repair work very carefully.
  1. Centerline drydocking – The differential pumping plan can be developed just as for the single ship drydocking, knowing the load distribution for each ship and assuming no ship load for the space between ships.
  2. Side-by-Side drydocking – Both longitudinal and transverse dry dock loading must be calculated. These are essential to minimize both longitudinal and transverse dry dock stresses.
  3. Echelon drydocking – Presents one of the more complex problems associated with multiple ship dockings. Longitudinal and transverse loading are a concern. In a floating dry dock, not only must longitudinal and transverse bending be monitored, but also twisting loads must be avoided. Well planned and executed differential pumping will eliminate this problem. Monitoring and control of twisting involves the following:
  4. The dry dock must be carefully monitored throughout the drydocking or undocking for torsional deflection. This monitoring cannot be done by checking the deflection along each wingwall, or by checking deflections across the dry dock.
  5. The twisting distortion can be most readily observed by detecting the displacement and direction of movement with transits established for diagonal as well as longitudinal and transverse checks of the dry dock’s reference plane.
  6. 9. Multiple Pairs, Abreast – Can present the same problem of twisting distortion as echelon drydocking. Thus, the same type of distortion monitoring should be employed. Multiple ship drydockings are most easily performed if ships are close to zero trim.

When two or more ships are to enter or leave the dry dock at the same time, it is advantageous if the Dock Master can concentrate upon one ship at a time. Differences in ship’s draft will often allow this approach. If a deep draft and a shallow draft ship are in dry dock, the shallow draft ship will lift off and clear the blocks while the deep draft ship remains firmly landed.

When two ships of the same drafts are drydocked, it is sometimes possible to arrange loading so that the draft differences allow significantly different landing or lifting off drafts. The same result can be obtained if the dry dock is prepared and blocked so as to land the first ship on a higher baseline than the second. In the case of centerline or echelon drydocking, moderate dock trims can also be used. The advantages are not only that the Dock Master can deal with the lifting off of one ship at a time, but if the first ship has to be relanded, the second ship is still firmly on the blocks and need not be refloated, unless desired. Note that ships in dry dock are idle ships. If the first ship floated has to be relanded, it is often desirable to completely undock both ships so that the second ship is out of the dry dock and then re-dry dock the first ship. The Dock Master must now organize and set the priorities of his intentions regarding this contingency.

VITAL NOTE: The ability to float off but one drydocked ship is an advantage of all dry docks except graving dry docks. In graving dry docks, since they must be flooded to harbor level, all ships in dry dock must be undocked and then relanded if they are to remain in the dry dock.

  1. Hauling a Ship in Off-Center

Modern ships often have appendages or protuberances that extend below the line of the keel. These include propellers, rudders, sonar domes, and a variety of transducers. In some cases, these are retractable and are specified to be above the keel line at drydocking. However, even in the retractable case, a malfunction of equipment can result in a below-keel obstacle.

It is essential that such a protuberance not strike the keel blocks for two reasons:

  1. The appendage may be damaged.
  2. The keel blocking or side blocking may be damaged.

The force that damaged an appendage may also cripple several blocks, or it may break a timber free so that it fouls another keel block, resulting in damage to the ship’s hull and to the blocking.

The Dock Master must control the ship’s movement into the dry dock so that he is sure of adequate clearance between the ship and appendages and the blocking system. The ideal situation would be to have a large depth of water over the blocks so that it would be impossible for inadvertent contact to occur.

In most cases, however, it is not possible to provide adequate depth over the blocks to do this. If the dry dock has ample width, a ship with a centerline appendage such as a sonar dome can be brought into the dry dock several feet off centerline. This will provide additional clearance depth relative to the height of the keel block system.

In planning, the Dock Master is well advised to work with cross sectional drawings of the dry dock and its block system, together with cross sections of the ship, so that he can easily visualize the actual amount of clearance between ship, dry dock, and blocks as the ship is moved into or out of the dry dock. By this method, he can develop an exact, safe approach for bringing the ship into the dry dock.

Note that this manner of handling the ship does have an additional hazard. In the case of adequate depth over the blocks, the blocks and the appendage cannot be damaged as the ship is positioned on the dry dock. But in this case, a deviation from the planned approach can cause damage. The Dock Master’s control of ship position must be such that he positively knows that the ship has not struck the blocking system during entry and positioning.

  1. Cold Weather Precautions

Below freezing weather presents major problems to ship repair work and to dry dock operation. The Dock Master should have a cold weather plan for his dock.

The following are typical items that should be noted:

  1. A ship docked under extreme cold weather conditions may face severe and unexpected problems. Waterborne, the underwater hull is never exposed to temperatures below 28 degrees. In a severe cold spell, a drydocked ship may have hull temperatures much lower than freezing for several days. This should be discussed at the Drydocking Conference.
  1. Both during drydocking and undocking, harbor ice may enter the dry dock. Plans to prevent ice interference with dry dock operations and for ice clearance must be made.
  2. Freezing will cause problems in ballast tanks, ballast lines, and in pontoon or basin drains. Do not overlook the chance of ice build-up in vent lines resulting in clogged tank vents.
  3. Freezing can cause inoperable or faulty reading of remote depth indicators.
  4. For both the ship and the dry dock; firemain, sanitary systems, and potable water will require precautions to prevent freezing.
  5. Deck machinery and other exposed systems need special attention.
  6. Extreme Overhangs

The case of a long overhang of the ship structure without block support usually arises in two instances:

  1. It is sometimes necessary to drydock a ship longer than the dry dock. In such a case, one or both ends of the ship overhang the dry dock.
  2. Certain types of ships, especially naval ships, tugs and trawlers, have a major cutaway of the hull aft so that the keel blocks do not bear on the after part of the hull.

The problem is usually not one of overall ship girder strength. Overhangs of 1.5 times the depth of the ship girder (main deck to keel) usually impose only modest stresses in the ship.

The Dock Master does have concern about both keel block loading and dry dock loading in the case of such overhangs. These issues deserve careful examination.

The Dock Master must recognize that the weight of the overhanging portion of a ship/s hull is being borne by the blocks and not by the section of the dry dock under the overhang. Thus, the dry dock loading calculations must be based upon the load carried by the keel blocks and not solely upon the longitudinal distribution of weight in the ship. It can occur that an end section of the dry dock carries no ship weight although a significantly large ship weight is located geometrically above it.

In the case of a ship which is cut away aft, there can be such an overload that the pressures on the blocks at the knuckle is beyond the crushing strength of the blocking. This will be found most often in the case of small ships, such as tugs, where there is a relatively long overhang combined with a very narrow bar keel or skeg at the after end of the keel bearing line. The high load can be spread to a larger keel blocking area by the use of steel plates on the top of the keel blocks with the soft crushing caps under the steel plate. This will distribute the concentrated load of the narrow skeg or keel. It is common practice to use butted blocks rather than spaced blocks in the knuckle region.

Self drydocking floating dry docks

Sectional floating dry docks are constructed so that it is possible to drydock sections of the dry dock in the remainder of the dry dock for repair and maintenance. The dry dock operating instructions for each dry dock detail these operations.

Some self drydocking floating dry docks are so constructed that it is possible to drydock the two end sections in the center section, or to drydock the center section upon the two end sections. The handling of the two end sections detached from the dry dock is a particularly critical operation. There are stages in the operation when the stability of the independent end sections is critical. Each end section must be flooded down so as to clear the center section, and then it must be further flooded down to a draft that will allow it to be drawn under the center section and the center section loaded on it and lifted clear by dewatering both end sections.

Before any self-drydocking maneuver, the Dock Master must be thoroughly familiar with all aspects of the operation as set forth in the Dry Dock Operating Manual. In addition to self-drydocking, the Dock Master should be thoroughly familiar with the capabilities of the dry dock as far as listing and trimming at light draft are concerned. Considerable repair and maintenance of certain underwater portions of the dock can be accomplished in this manner without the need for disassembly and self-drydocking. Dry dock stresses and stability need careful attention when attempting such operations.

Unusual Weight Concentrations

When waterborne, each portion of the ship is supported by the buoyancy forces acting along the ships underwater hull. The strength of the ship’s hull structure distributes these weight concentrations along the hull. The hull flexes to accommodate this distribution of load, and of course flexes to respond to the loads imposed by the action of the sea.

In a graving dry dock, with its fixed and nearly unyielding concrete floor, the concentrated weights in the ship are transmitted directly from the ship to the keel blocks and to the dry dock floor. Soft cap blocking does permit some deflection of the ship’s hull and redistribution of the load; however, current keel blocking practice using concrete blocks with only a small amount of timber allows but little compression for load redistribution.

In contrast, the floating dry dock is an elastic structure, roughly as flexible as or even more flexible than the ship itself. The maximum load a dry dock section can provide to support the ship above it is limited to the displacement of that section of the dry dock less the dry dock weight and the weight of contained water.

The longitudinal bending flexibility of the dry dock and ship will distribute the concentrated load when the lift of the dry dock is at a point exceeded by the weight of the ship above it. Thus, the floating dock is kinder to the ship’s structure than is the rigid graving dry dock. However, the differential pumping plan has to be followed with care so as to control the stresses imposed upon the dry dock itself.

From his differential pumping plan, the Dock Master can estimate the load being carried by each section of the dry dock, and thus the average keel block load and pressure on the blocks in that section. For the case of very heavy shipboard weight concentrations, calculation of these block loads and pressures is warranted. It may be found that additional block area is desired to reduce the effect of anticipated values.

The same sort of calculation is advisable in the case of a damaged ship where many keel blocks may have been omitted. Knowing the lifting force the dry dock section allows estimating the total block area to be arranged so that reasonable block pressures and loads result.

Some ships in themselves constitute a weight concentration when placed in a floating dry dock. Both submarines and icebreakers are uncommonly heavy for their length. This means that they will produce unusual loading of a dry dock. In preparation for the docking of such ships, the Dock Master should review Docking Plans with care together with the structural limitations of the dry dock. Special blocking arrangements to distribute the concentrated load of a submarine or of an icebreaker may be required. Some dry docks have been specially reinforced to enable them to dock submarines.

Drydocking Ships with Shores

When designing a docking plan for a ship, we soon learn the importance of taking the majority of the weight on the keel, with the bilge blocks only serving to keep the ship upright, typically carrying only 15% to 25% of the total weight of the ship. If this maxim is forgotten, there is sure to be damage because the bilges of a ship are typically not strong enough to take any more weight (note-some wide flat bottom vessels are designed with keel blocks supporting 33-50% of the ship’s weight and the bilge blocks on each side of the vessel supporting 17-25% of the ship’s).

But why not take ALL of the weight on the keel, and use shores to prevent the vessel toppling over?

History

When graving docks were first invented this was the normal way of docking a ship. Bilge blocking was introduced long after ships were being regularly docked with side shores, and it was only accepted as a normal alternative when ships started to be built without deadrise.

We do not operate a dry dock ourselves but my company (Butchdesign sas) is frequently asked to provide technical help for drydocking yachts and small ships in other yards. There are a few graving docks in the world where they still prefer to use shores to support a ship. Two of our clients, one in Marseille and the other in Martinique, are among them.

Although the normal excuse is simply that “We have always done it this way”, there are some very good reasons why the old way is often better than the new:

  1. There is no problem if the underwater shape of the ship is unknown. A conventional docking plan is not necessary.
  2. Apart from the bottom of the keel the entire underwater surface of the hull is exposed for repair, cleaning or repainting.
  3. It saves time because a series of ships can be drydocked without needing to drain the dry dock between each one for moving bilge blocks. *
  4. The longitudinal positioning of the vessel in the dry dock is less critical than it is when bilge blocks are used.
  5. A vessel with a substantial deadrise in the bottom of the hull puts a lateral load onto bilge blocks that require special provisions for holding them in place. This is not a problem with side shores.

* This assumes that they all have a horizontal keel, although it also applies to a series of vessels with the same rake of keel. (Technically the crush blocks should be replaced each time but this is not always done.)

Dry Dock

Traditionally, graving docks were built with steps each side, specifically so that shores can rest on a step at a height suitable for the vessel being drydocked and butt up against a solid backing to take the compression load.

Shores butted against these steps are held firmly and will not slip.

In order to use shores, it is much simpler if the graving dock has similar steps to this one and also the drydock must not be too wide. You cannot drydock two vessels side by side.

Method

The vessel is brought into the drydock.

In each position designated for a shore, a pad with a soft surface against the hull is placed on the topsides and secured in position. The pads have a socket to locate the shore.

The pads are generally placed at the level of the main deck, aligned with a bulkhead. They can also be placed on a rubbing strake, but in this case the pad should be specially shaped.

The water is pumped out of the dock as normal. When the vessel has just touched over the full length of the keel, pumping is stopped and shores are placed in position with a crane. The outboard end of the shore rests on a step. Wedges are placed between the end of the shore and the riser of the next step. Note the angle of the shores. The end on the ship must be higher than the end on the drydock wall.

The shores are either solid wood or steel tubes, approximately 200-300mm diameter, but this varies with the size of ship and the unsupported length of the strut. The big advantage of using wooden shores is that they can be cut to length with a chainsaw as required. (Inevitably this means that shores are slowly shortened with repeated use, and replacement shores have to be provided at maximum length from time to time.)

After the shores are in position, the pumping can restart.

When the vessel has settled, the wedges are hammered home. Note that as the sacrificial soft-wood caps on the keel blocks are crushed down, the descent of the ship compresses the shores.

On the right we are supporting this ketch entirely on its external keel. There is no risk in doing this provided the longitudinal centre of gravity is over the bottom of the keel and provided the rig is still in place. This allows the stays that hold up the mast to hold up the ends of the vessel. However, we did put in a bow support when a gale was forecast.

A more extreme example (which we were not involved with) is the docking of “Reliance”, the Herreshoff design for the America’s Cup. In this case the bow support would only have been placed after the dock had been largely pumped out. Reliance in the Erie Basin drydock, Brooklyn, on August 17th, 1903

Note how difficult it would have been to support Reliance in the drydock with bilge blocks.

The French navy was perfectly happy for us to dry dock their ships with shores in Martinique.

And there is no limit to the size of ship that can be supported in this way, although super tankers and other large ships with flat bottoms are better suited to being supported on bilge blocks.

Docking Plans

A docking plan for a ship being supported with shores is a very simple document, but it is specific to the graving dock. You need an accurate plan of the dry dock to prepare one.

On a single sheet we show sections of the vessel at each shore:

And on a second sheet we show plan & elevation views of the setup.

In addition to the drawing we would normally include a calculation (top right above and enlarged on left) to indicate the safety factor we are working to.

In Martinique the trade winds blow down the axis of the dock, not across it so the maximum wind is assumed to be relatively light. If the docking is done during the hurricane season a higher wind strength would be used.

Underneath the calculation there are various notes covering, for instance

  • The precautions to be taken to protect the paintwork.
  • That the struts (or shores) are to be made of 10” (273mm) diameter schedule 40 (9.3mm wall) mild steel pipe.
  • A table giving the lengths of all the shores required for the drydocking but we also point out that strut lengths are approximate and direct measurements should be made on site for confirmation.
  • Etc.

Technical aspects

We have only worked with drydocks that already have their own steel or wooden shores. If steel, the yard will provide a list of all the lengths available and it is generally possible to adapt the layout of shores so they match the available lengths.

If we need to mount shores towards the bow or stern, we orient them to they remain at right angles to the hull, or at least have the same angle to the hull as they have to the dock wall. This reduces the risk of them sliding out sideways, but we put lateral guy ropes onto the struts at both ends to be sure.

In the absence of wind, if the vessel is upright when brought into the drydock one can assume that its transverse centre of gravity is on the centreline. In this case the only load on the shores is going to be due to wind. However, when calculating the shores we assume a heel angle to account for any elasticity in the system. Bearing in mind that the hull itself is largely shielded from the wind by the sides of the dry dock, the overturning moment is not very high, and you can mathematically justify putting in very few side supports. However, we generally put in enough shores each side to keep the owner and crew happy. when looking through historical photographs it is reassuring to see how few shores were habitually used in the past.

A few years ago we had a French navy frigate in the graving dock in Martinique when I was horrified to hear reports of an earthquake having hit the island. I immediately rang the Dock Master and I was very relieved to be told that although the shores had bounced around during the ‘quake, when it was all over they were still in place and apart from swaying about a bit, the vessel itself hadn’t moved!

  1. Shores are a great way of supporting a ship in a drydock. Perhaps we need to turn the clock back and rediscover the old way (…more)

 

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