MGN165 Amendment 2 — Fishing Vessels: The Risk of Flooding

29 Vessels Lost, Same Cause, Eight Years Running

Between 2016 and 2024, 86 UK fishing vessels were involved in flooding or foundering incidents. Twenty-nine of them were lost. MAIB investigations into fishing vessel losses keep coming back to the same root cause: flooding, usually starting small and unnoticed, not a single dramatic hull breach. On 23 July 2026, the MCA published MGN165 Amendment 2 (F), updated guidance on bilge systems and flooding prevention aimed at designers, builders, owners, skippers and crew.

The Legal Minimum, by Vessel Size

Mandatory bilge system requirements already exist, set out across three size-banded instruments: MSN1871 (under 15m LOA), MSN1872 (15m to under 24m registered length), and MSN1873 (24m registered length and over). MGN165 Amendment 2 sits on top of these as recommended good practice — the kind of thing worth doing even where it isn't the strict legal minimum for your vessel's size band.

What the Updated Guidance Actually Recommends

• Bilge alarms in fish holds and compartments below the waterline, with a secondary alarm at a higher level on a separate power supply — so one point of failure doesn't take out your only warning.
• “Circuit healthy” indicators, so you know the alarm itself is working, not just silent because there's nothing to detect.
• Weekly bilge pump tests, daily alarm tests — not just at survey time.
• Monthly valve exercising (open/close every valve to stop it seizing) and weekly strainer cleaning.
• Minimise sea inlet valves, use corrosion-resistant materials, and reject bandaged repairs or welded patches on pipework — a known failure point on older vessels.
• Label every watertight compartment “TO BE KEPT CLOSED AT SEA,” and actually keep weathertight closures shut when not in use.

Shelter Deck Vessels (15m–24m, Built Before 23 November 2002)

If that's your vessel, MGN165 Amendment 2 flags specific drainage requirements: rapid drainage via scuppers or tonnage valves, an independent wash-water pump capable of at least 1.5× the supply rate, and powered drainage if the tonnage valves would immerse at 10° of heel or less. Unattended deck wash pumps are specifically flagged as a risk — don't leave one running unsupervised.

If Flooding Actually Starts

The guidance is blunt about sequence: alert the Coastguard immediately via DSC, get lifejackets on, check every plausible point of water ingress, close the relevant sea valves, get bilge pumps running, and keep the Coastguard updated as the situation develops — don't wait until it's clearly serious to make the first call. Monthly emergency drills are mandatory, with a debrief afterward to catch what didn't go to plan.

The Real Point

None of this is complicated engineering. It's mostly maintenance discipline — testing things that are easy to assume are fine, and not letting a bandaged pipe repair become permanent. The vessels lost in MAIB's flooding statistics weren't, on the whole, lost to freak events; they were lost to small, known gaps that had been living on a boat for a while before the day it mattered.

Test Your Knowledge

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Related Reading

• Cornishman — another fishing vessel investigation where a known, ordinary-looking gap was the real cause