Boat traffic, and being seen from the surface
Explainer · Last reviewed 2026-08-17
A diver at the surface is almost invisible from a boat at any distance, and propeller strike is a recognised cause of death — which is why the float is safety equipment before it is fishing equipment.
Safety
Boat traffic and being seen — Can cause serious injury or death
A diver at the surface is effectively invisible to an approaching vessel. Propeller strike is a recognised cause of death and injury among spearfishers and freedivers.
What reduces it: A large high-visibility float carrying the locally recognised dive flag, avoiding channels and moorings, planning around traffic and light, looking up on ascent, and surfacing with a raised hand.
A person in the water presents almost nothing to see. A head is small, dark, at wave height and moving with the surface, and a helmsman scanning ahead at planing speed will not pick one out in time to alter course. Add chop, sun glare or low light and the effective detection distance falls close to zero.
The consequence is that a diver relying on being seen is relying on nothing. What can be seen is a float: large, brightly coloured, held high, and — where the local convention uses one — carrying a dive flag.
FLAGS AND CONVENTIONS DIFFER. The blue-and-white Alpha flag is the international signal for a vessel with a diver down and restricted manoeuvrability; the red-and-white diagonal is used in North America and elsewhere for divers in the water. Which applies, and what obligations it places on passing vessels, is a local regulatory matter — and this is one of many places where FishingHQ explains the concept and points the reader at their own maritime authority rather than stating a rule.
WHAT THE FLOAT ALSO DOES. It marks the diver's position for the buddy, gives a resting point at the surface, carries the catch away from the diver's body, and provides something to hold in a current. The safety functions and the practical ones are the same object, which is why a float is not optional equipment in any serious account of the discipline.
Where the risk concentrates
Boat traffic is not uniform. It concentrates in channels, around harbour entrances and moorings, along popular coastal routes and at the times of day when leisure craft are moving.
A diver planning a session should know where the traffic is before entering the water, and should treat channels as areas to cross deliberately rather than to hunt in. Surfacing under a boat is a specific and preventable event.
LOW LIGHT MULTIPLIES EVERYTHING. Dawn and dusk are good diving conditions and bad visibility conditions for the people who need to see you. Reflective tape on a float, a high-visibility float colour and a light where appropriate all help, and none of them substitutes for staying out of traffic.
AND SURFACING DELIBERATELY. Looking up on ascent, and surfacing with a hand raised, is standard practice for exactly this reason — it puts the diver's eyes on what is above before their head arrives there.
Authoritative guidance
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on surface marking, dive flags, boat traffic and surfacing procedure.States this directlyCitation checked — the work exists and is described correctly
- RNLI water safety guidance: cold water shock and Float to Live — Royal National Lifeboat Institution (Water-safety or diver-training authority)Relied on for: Water safety guidance on visibility, cold water and the difficulty of spotting a person in the water.Background and mechanism onlyPassage read and verified
Where to go next
Where it matters
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Shore diving
Where the exposure is highest for shore-based divers.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on surface marking, dive flags and vessel traffic.States this directlyCitation checked — the work exists and is described correctly
Gear this affects
- Dive floats and float linesA float is the only thing about a diver that a helmsman can realistically see.
- Suits, masks, fins and cutting toolsHigh-visibility colour and reflective tape extend the distance at which a diver can be picked out.
- Surface marking and signallingFlag conventions differ by jurisdiction, and what obligations they place on passing vessels is a local matter.
What these connections rest on (3)
Authoritative guidance — 3 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Dive floats and float lines
The float's primary function is visibility rather than fishing.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on surface marking, dive flags and vessel traffic.States this directlyCitation checked — the work exists and is described correctly
Suits, masks, fins and cutting tools
The equipment answer to a detection problem.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on surface marking, dive flags and vessel traffic.States this directlyCitation checked — the work exists and is described correctly
Surface marking and signalling
Signalling equipment exists for this hazard and its rules are regional.
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance on surface marking, dive flags and vessel traffic.States this directlyCitation checked — the work exists and is described correctly
Sources for this page
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance including surface marking and vessel traffic.States this directlyCitation checked — the work exists and is described correctly
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