Why marine casualty disputes are different
Few areas of litigation are as fact-intensive as a marine casualty. A collision or grounding is over in minutes, but the evidence is scattered, technical and perishable: voyage data, radar plots, bridge audio, engine movements and witness accounts. A court rarely holds the seafaring knowledge needed to read it, which is exactly why a credible expert is so often decisive.
The instructing team's first job is not analysis but preservation. Voyage Data Recorders (VDRs), required under the IMO SOLAS Convention, overwrite on a loop, often within 12 to 48 hours. Engine and ECDIS logs can be lost on the next voyage. The single most valuable thing you can do in the first day of a marine casualty is secure that data, ideally with an expert already advising on what to ask for.
When to instruct
Instruct as soon as a casualty looks likely to become a claim. Early involvement lets the expert guide evidence preservation, attend any joint survey, and frame the technical questions before positions harden. Waiting until pleadings are exchanged often means working from a degraded record.
Early instruction also helps you test your own case honestly. A good marine expert will tell you where the navigation was sound and where it was not, and that candour is worth far more than a convenient opinion that collapses under cross-examination.
Matching the expert to the issue
"Marine expert" is not one discipline. A collision turns on navigation, watchkeeping and the COLREGs, which is the province of a master mariner or casualty investigator. A question of stability, structure or whether a vessel was fit for service calls for a naval architect. A machinery breakdown or propulsion failure needs a marine engineer. Many casualties need more than one.
Getting this match right at the outset avoids the costly situation of a well-credentialled expert opining slightly outside their true competence, something opposing counsel will find quickly.
What a casualty report should establish
A persuasive casualty report reconstructs events from the evidence rather than asserting a conclusion. It sets out the agreed facts, the data relied on, the assumptions made where data is missing, and a reasoned account of cause and contribution. Where the COLREGs (the IMO Collision Regulations) are in play, it should map the conduct of each vessel against the rules: give-way and stand-on obligations, lookout, safe speed and the actions a prudent mariner would have taken.
Crucially, it should be candid about uncertainty. A report that overclaims, attributing precise blame the data cannot support, invites a damaging cross-examination. The expert's overriding duty is to the court under CPR Part 35, and the strongest reports read as though written for the tribunal, not the client. If you are new to the process, our guide on how to instruct an expert witness sets out the essentials.
Single joint expert or party-appointed?
In narrowly technical or lower-value casualties, courts and arbitrators increasingly favour a single joint expert. Where the issues are central and genuinely contested, say a high-value collision with disputed navigation, each party may instruct its own, with a joint statement narrowing the differences before trial. Consider the proportionality question early, because it shapes how you scope the work and the budget.