A detailed study into the safety of roll-on/roll-off (Ro-Ro) ferries has revealed critical discrepancies between theoretical stability assumptions and actual operational practices, culminating in a new, evidence-based recommendation for maximum wave height limits. The research highlights how common onboard conditions, particularly openings on the vehicle deck, significantly impact vessel stability and safety.

**Background: The Gap Between Theory and Reality
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In standard maritime procedure, the stability approval process for a vessel is conducted under the assumption that all openings on the main or freeboard deck are securely sealed and watertight. This theoretical condition ensures that the compartments below the freeboard deck contribute fully to the ship's buoyancy. However, investigations from previous vessel accidents indicate that a primary cause of total loss is the ingress of water into compartments at a rate that exceeds the capacity of pumps or other dewatering methods.

This study was initiated to bridge the gap between these theoretical evaluations and real-world scenarios. Its central objective was to define a safe operational wave height limit for ferries by analyzing the actual conditions found in the field. As a preliminary reference, the research acknowledged the safety advice from Indonesia's Meteorology, Climatology, and Geophysics Agency (BMKG), which identifies wind speeds over 21 knots and wave heights exceeding 2.5 meters as high-risk conditions for ferry crossings.

Methodology: A Two-Pronged Approach

To achieve its objective, the research employed a two-part methodology combining on-site verification with advanced computational analysis.

Field Surveys: Investigators conducted comprehensive field surveys to gather data on the actual operating conditions of ferries. This phase involved direct observation and interviews with operators and crew members across 30 Ro-Ro ferries. The surveys were focused on six key crossing routes in Indonesia:

Tanjung Api-api – Muntok (6 vessels)

Merak – Bakauheni (5 vessels)

Ketapang – Gilimanuk (4 vessels)

Padangbai – Lembar (5 vessels)

Kayangan – Poto Tano (8 vessels)

Bira – Pamatata (2 vessels)

Stability and Seakeeping Analysis: The data collected from the field surveys served as direct input for sophisticated stability and seakeeping analyses. Using Maxsurf Stability and Motion software, researchers modeled vessel behavior to determine the maximum wave height that would lead to water reaching the identified openings on the freeboard deck.

**Results and Key Findings
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The analysis yielded several critical insights into common operational practices and their impact on vessel safety.

Operational Findings from Field Surveys:

Openings on Deck: A striking 97% of the surveyed ferries operated with openings on the vehicle deck left open. These openings, which include doors, small hatches, manholes, and other access points to the compartments below the freeboard deck, directly compromise the watertight integrity assumed in stability calculations.

Cargo Securing: The study found that vehicle cargo is generally not lashed down. While some vehicles were chocked with wooden blocks, the lack of proper lashing presents a significant risk of cargo shifting in rough seas.

Cargo Arrangement: Vehicles are typically arranged parallel to the vessel's length. An exception was noted on the Ketapang-Gilimanuk route, where side-loading ramp doors necessitate that some vehicles are parked transversely, potentially altering the vessel's center of gravity and response to rolling motions.

Computational Stability Analysis:

Downflooding Angle (DF): The downflooding angle—the angle of heel at which water begins to enter the vessel through deck openings—was found to be between 8.2∘ and 26.6∘. The average DF was 18.26∘ for a fully loaded condition and 16.08∘ for a 30% overload condition. The analysis also showed a positive correlation where larger vessels tended to have a larger downflooding angle.

Cargo Shift Precedes Downflooding: A crucial finding was that the angle at which cargo begins to shift is reached before the downflooding angle. The analysis determined that a truck is likely to shift at a heel angle of 15∘and a car at 18∘. In an overload condition of 30%, a truck shift would occur concurrently with the vessel reaching its downflooding point. In a standard full load condition, both truck and car shifts would have already occurred by the time the vessel heels to the point of downflooding. This creates a dangerous cascading effect where a loss of stability from shifting cargo exacerbates the risk of taking on water.

Conclusion and Recommendation
The study concluded that the wide variety of hull designs among the sample ferries led to a scattered distribution of wave height results. However, the consistent and critical field findings—namely the prevalence of open access points on the freeboard deck and the lack of vehicle lashing—point to systemic risks not accounted for in standard stability approvals.

Based on the comprehensive analysis of these real-world conditions, the research establishes a definitive operational limit. The study recommends that the maximum wave height for the operation of Ro-Ro ferries should be limited to 2.37 meters. This data-driven recommendation provides a crucial new safety benchmark designed to mitigate the risks identified through the investigation