Blog Post 07: Repair Afloat vs Dry Dock — How to Decide
Title: Repair Afloat vs Dry Dock: How to Decide for Your Vessel
Target Audience: Technical Superintendents, Fleet Managers, Shipowner Directors, Operations Teams.
Core Keywords: Repair Afloat, Dry Dock, In-Water Survey, IWS, Decision Framework, Off-Hire, Cost Comparison, Operational Window, Class Survey, Regulatory Compliance.
The Decision That Every Superintendent Faces
At some point in every vessel's operational life, a repair is needed, and the question arises: can this be done afloat, or does it require a dry dock?
The answer is rarely binary. Most repairs occupy a grey area where afloat execution is technically feasible but requires specific conditions — weather, permits, Class approval, operational schedule. The decision framework is not "afloat vs dry dock" but rather "under what conditions can this repair be safely and compliantly executed afloat, and when does the risk or cost of afloat execution justify the greater cost and off-hire of a dry dock?"
This article provides a structured framework for making that decision.
The Decision Framework
The decision between afloat repair and dry docking rests on four axes:
1. Regulatory and Class feasibility. Can this repair be executed afloat under the applicable Class society rules and flag State requirements? IACS UR Z10.2 defines the conditions for in-water surveys, but individual Class societies may impose additional restrictions on specific repair types — particularly hot work, structural welding, and repairs affecting statutory systems.
Action: Submit the repair scope to the attending Class society for a preliminary assessment before committing to either path.
2. Operational window and schedule impact. How long will the vessel be available at the operational location, and does this window align with the conditions required for afloat repair (weather, sea state, daylight, permit acquisition, surveyor availability)?
| Factor | Afloat Repair | Dry Dock |
|---|---|---|
| Off-hire duration | 2–5 days (typical) | 10–20 days (including transit, docking, undocking) |
| Schedule flexibility | Dependent on weather and port window | Fixed by shipyard booking |
| Location dependency | Must be at a suitable port or anchorage | Must transit to shipyard location |
3. Technical complexity and risk. Is the repair within the scope of proven afloat techniques, or does it require the controlled environment of a dry dock? Steel renewal below the waterline, stern tube work, and major machinery overhauls typically favour dry docking. Hull cleaning, anode replacement, valve overhauls in accessible locations, and non-structural welding are routine afloat repairs.
4. Total cost comparison. The cost comparison is not afloat cost vs dry dock cost in isolation. It must account for:
- Direct repair cost (materials, labour, equipment).
- Transit cost and off-hire to reach the shipyard.
- Mobilisation cost for afloat intervention team.
- Risk-adjusted cost: probability of scope growth in either scenario.
- Opportunity cost: what else could the vessel be earning during the additional off-hire days?
When to Choose Afloat Repair
Afloat repair is the preferred option when the following conditions are met:
- Regulatory acceptance is confirmed. The Class society and flag State have confirmed, in writing, that the proposed repair method is acceptable afloat.
- The operational window is sufficient. Weather, sea state, and port or anchorage conditions are within acceptable parameters for the full duration of the intervention.
- The scope is well-defined and contained. The repair is limited to known defects without high probability of hidden additional findings (which is the risk of afloat repair: if unexpected structural issues are found, the vessel may still need to dry dock, incurring both costs).
- The cost advantage is clear. Total cost (intervention + off-hire + risk contingency) is significantly lower than dry dock cost.
Typical candidates for afloat repair:
- Propeller polishing and blade fairing.
- Anode replacement.
- Sea chest cleaning and valve overhaul (with cofferdam).
- Non-structural welding above or near the waterline.
- In-water surveys (IWS) for Class credit.
- Rudder inspections and minor repairs.
When to Choose Dry Dock
Dry docking is the appropriate choice when:
- The repair affects structural integrity below the waterline. Steel renewal in way of the hull shell, bilge keels, or critical structural members below the waterline is not reliably executable afloat.
- Class requires dry dock attendance. Some Class surveys (e.g., special survey, tail shaft survey) mandate dry docking.
- The operational window is not reliable. If weather conditions in the operating area make it unlikely that the afloat repair can be completed within the available window, the risk of aborting the afloat intervention and still needing to dry dock outweighs the potential cost saving.
- The scope is uncertain. If the full extent of the repair cannot be determined without opening up the system in a controlled environment, dry docking provides the certainty that afloat repair cannot.
Typical candidates for dry dock:
- Major steel renewals (shell plating, deck plating).
- Tail shaft survey and stern tube seal replacement.
- Boiler survey and repairs.
- Ballast tank full coating renewal.
- Major machinery removals requiring crane access.
The Hybrid Scenario
Some repairs can be partially executed afloat and completed in dry dock. For example:
- An in-water survey identifies a rudder bearing issue that can be diagnosed afloat but requires dry docking for the full repair.
- A pre-docking survey (afloat) confirms the steel renewal scope, allowing the shipyard to prepare materials and plan the work before the vessel arrives — reducing dry dock time.
In these cases, afloat work reduces the dry dock scope rather than eliminating it entirely, which still reduces total off-hire and cost.
Decision Matrix Summary
| Condition | Afloat Repair | Dry Dock |
|---|---|---|
| Class acceptance confirmed | Proceed | — |
| Structural repairs below waterline | — | Proceed |
| Well-defined, contained scope | Strong candidate | — |
| Uncertain scope, high finding probability | — | Strong candidate |
| Reliable operational window (weather, port) | Proceed | — |
| Unreliable or short operational window | — | Proceed |
| Total cost (incl. risk) lower | Preferred | — |
| Total cost (incl. off-hire transit) lower | — | Preferred |
Atlantech Marine's Approach
We assess every repair on its technical, regulatory, and operational merits before recommending afloat or dry dock execution. Our team prepares the method statement, coordinates Class acceptance, acquires the necessary permits, and executes the intervention to the same standard regardless of location.
If afloat repair is feasible, we execute it with full documentation and Class coordination. If dry dock is the right answer, we plan and supervise the docking. We do not have a preferred method — we have a preferred outcome: a controlled, documented, compliant repair.
Need help deciding? Submit a service request with the vessel location and defect description, and our technical team will assess both options.
Atlantech Marine — Afloat repair and dry dock supervision for mid-size shipowners. Based in Malta. Operating across the Mediterranean and West Africa.
