This article isn't legal advice: your DPA, your flag state and your management company are the authoritative sources for what your vessel must do. What follows is the baseline under SOLAS Chapter III and how it tends to land on a working yacht.
The rule crews ask about most often is the one that bites hardest in the season, when people join and leave in ones and twos: if more than 25% of the crew has not taken part in an abandon ship drill and a fire drill on board that particular ship in the previous month, drills must be held within 24 hours of the ship leaving port.
It is about participation, not headcount on the crew list
The wording matters, and it is the part most often misread. The test is not "have more than a quarter of the names on my crew list changed". It is whether more than a quarter of the people currently on board have not participated in those drills on this vessel in the previous month.
Two crew members who joined three weeks ago and drilled on board last week do not count towards the 25%. A crew member who has been aboard all season but missed last month's drills does. So does someone who has drilled extensively — on their previous boat.
That last case catches people out. Experience does not transfer. The drill has to have happened on this ship, because the point of it is knowing this vessel's stations, this vessel's escape routes and this vessel's equipment.
Working out whether you are over the line
The calculation is simple arithmetic on the crew actually on board:
- Count everyone on board who is part of the muster organisation
- Of those, count how many have not taken part in both an abandon ship drill and a fire drill on this vessel in the previous month
- If that second number is more than a quarter of the first, the 24-hour clock applies on your next departure
On a yacht with twelve crew, four people who have not drilled puts you over. On a crew of eight, three does. The margins are small, which is why the answer on most yachts is to drill after a crew change rather than to work out whether you have to.
Why yachts trip over it more than merchant ships
A cargo ship changes crew in blocks, on a schedule, in port. A yacht changes crew continuously through a season — a stew leaves in Antibes, a deckhand joins in Palma, someone goes home sick mid-charter. Nobody experiences that as "a crew change", so nobody starts the clock. The 25% threshold gets crossed a person at a time.
The other yacht-specific trap is the definition of "leaving port". A vessel moving from a marina berth to an anchorage a mile away, or repositioning between two ports on the same coast, has still left port. Short hops do not exempt you.
New vessel, major modification, new crew
Alongside the 25% rule sits a stricter one: when a ship enters service for the first time, after a modification of a major character, or when a new crew is engaged, the drills are held before sailing — not within 24 hours of leaving port.
For a yacht coming out of a yard period with a substantially new crew, both conditions can apply at once. In practice the safe reading is the stricter one: drill alongside, before you go anywhere.
Evidencing it, which is where most vessels come unstuck
Knowing you drilled is not the same as being able to show it. An auditor or a port state inspector asking about the 25% rule is asking a question about records: who was on board, who took part, on what date, in what scenario.
A log book entry saying "abandon ship drill carried out" answers none of that. What answers it is a per-person record — and that is the awkward part to keep by hand, because the crew that changes is exactly the crew whose participation you are trying to track.
How The Muster App helps: every drill run on the iPad records which crew members mustered, by name, with a timestamp and the scenario. Because crew are added and removed in the admin panel as they join and leave, the Sessions log shows participation against the crew who were actually on board that day. When someone joins mid-season, their record starts empty and stays visible — so the question "who on this boat has not drilled since joining?" has an answer you can read rather than reconstruct.
The practical policy most yachts settle on
Captains who stop worrying about this rule tend to have adopted one of two habits:
- Drill on the crew change. Anyone new does an abandon ship and fire drill in their first days on board, before the boat moves. The 25% question never arises because nobody is ever outside the previous month.
- Drill on a fixed date each month, and catch joiners with a short familiarisation drill when they arrive. This suits vessels with a steady programme and a predictable crew.
Both satisfy the rule. Neither requires anybody to do the arithmetic under pressure on a departure morning, which is the real value of having a policy at all.
Related reading
- How often must drills be run? — the monthly rule per crew member and the weekly rule on passenger ships
- SOLAS and ISM drill requirements — the full baseline these rules sit inside
- Crew familiarisation — ISM 6.3's before-sailing instructions for anyone joining