Handling in different conditions
What to do before and when the weather turns: reading the forecast, the different kinds of seas, bars, fog, wind at the dock and at anchor, and emergencies.
Forecasts & warnings
- Reading the marine forecast Power & sail
The National Weather Service (NWS) forecasts marine weather by zone. Know which zones you boat in, where to hear the forecast aboard, what the numbers really mean and what each headline means. Small Craft Advisory thresholds differ by region and even by office.
Sea state
- Wind, waves and swell Power & sail
Wave size depends on how hard the wind blows, for how long, and over how much open water. Swell arrives from distant storms. The wave period tells you how steep the sea will feel: at the same height, a shorter period is rougher and more dangerous. - Beam seas and rolling Power & sail
Seas on the beam make a boat roll hard, and a breaking wave on the beam can knock it down. Zigzag across the seas instead of running broadside, turn to meet any wave that looks like breaking, secure everything aboard, and use stabilizers or flopper-stoppers if you have them. - Wind against current and tide rips Power & sail
When wind or swell runs against a strong tidal current, waves get shorter, steeper and quicker to break. Plan passes, straits and bars for slack water or a fair current using current predictions, not tide times.
Boat handling
- Running into head seas Power & sail
Driving into the seas pounds the boat and the crew. Slowing down, trimming the bow down and taking the waves a little off the bow usually give a safer, drier ride. Decide early whether to carry on, change course or turn back. - Running with following seas Power & sail
Seas from astern can lift the stern, take away your steering and swing the boat broadside (a broach). Control speed so the boat stays under command, keep the stern square to steep seas and keep watching astern. Skippers disagree about drogues and other storm tactics. - Crossing a bar or inlet Power & sail
River and harbor bars can turn deadly in minutes when swell meets shallow water and an ebb current. Check Coast Guard bar conditions and restrictions before you go, plan to cross with the flood, watch the sets from outside, and wait at sea rather than force a crossing. - Docking and undocking in wind and current Power & sail
Wind and current do much of the work when docking, for you or against you. Know how prop walk, twin engines or a thruster move your boat, approach slowly into the stronger of wind or current, and let spring lines do the heavy lifting. - Anchoring as the wind rises Power & sail
An anchor that held in the afternoon calm may not hold in a night blow. Anchor with enough scope for the wind you expect, confirm the anchor is set, watch for dragging, and decide early whether to add scope, re-anchor or leave. - Sailboats: reducing sail and heaving to Sailboats
On a sailboat the first defense against rising wind is less sail, set early. Know how to reef your boat before you need to, reef when you first think of it, and learn to heave to so you can stop, rest or ride out bad weather.
Fog & night
- Fog and restricted visibility Power & sail
In fog the Navigation Rules change how you must behave: go at a safe speed with engines ready, keep a lookout by sight and hearing, sound the fog signals and use radar properly. AIS helps, but many boats don't transmit it. - Running at night Power & sail
At night you navigate largely by the lights other vessels show. Learn the common light patterns from Rules 20 to 31, keep your own lights right, and protect your night vision: it takes many minutes to build and is lost in a moment.
Emergencies
- Thunderstorms, squalls and lightning Power & sail
Thunderstorms and squalls bring sudden violent gusts, wind shifts, lightning, blinding rain and sometimes waterspouts. The best defense is not being out in them: watch the forecast and the sky, head for shelter early, and know what to do if one catches you. - Crew overboard Power & sail
A person in the water can be lost from sight in seconds and, in cold water, may have only minutes of useful strength. Shout, point, throw flotation, mark the position and stop near them. Getting a person back aboard is often the hardest part: plan and practice it on your boat. - Cold water immersion Power & sail
Falling into cold water can kill within minutes through gasping and loss of muscle control, long before hypothermia sets in. Wear a life jacket, dress for the water temperature, and know what to expect and what to do in the first minutes.
Preparation
- Heavy-weather preparation Power & sail
Most heavy-weather trouble is avoided before leaving the dock: a good forecast, a float plan, a boat secured for sea and a briefed crew. If you are caught out, slow down or reef early, get everyone into life jackets and harnesses, and head for shelter while you still can.
Reference tables
Beaufort wind force scale
| Force | Wind (knots) | Name | Wave height, open sea: typical (max) | What the sea looks like |
|---|---|---|---|---|
| 0 | Less than 1 | Calm | 0 ft | Flat and glassy. |
| 1 | 1-3 | Light air | Under 1/2 ft | Scaly ripples, no foam crests. |
| 2 | 4-6 | Light breeze | 1/2 ft (1 ft) | Short small wavelets; crests look glassy and don't break. |
| 3 | 7-10 | Gentle breeze | 2 ft (3 ft) | Larger wavelets; crests start to break; a few scattered whitecaps. |
| 4 | 11-16 | Moderate breeze | 3 ft (5 ft) | Small waves getting longer; whitecaps fairly common. |
| 5 | 17-21 | Fresh breeze | 6 ft (8 ft) | Moderate, longer waves; many whitecaps; some spray. |
| 6 | 22-27 | Strong breeze | 9 ft (12 ft) | Large waves forming; white foam crests everywhere; likely some spray. |
| 7 | 28-33 | Near gale | 13 ft (19 ft) | Sea heaps up; foam from breaking crests starts to blow in streaks downwind. |
| 8 | 34-40 | Gale | 18 ft (25 ft) | Higher, longer waves; crest edges blow off as spindrift; clear foam streaks. |
| 9 | 41-47 | Strong gale | 23 ft (32 ft) | High waves; dense foam streaks; crests topple and roll over; spray can reduce visibility. |
| 10 | 48-55 | Storm | 29 ft (41 ft) | Very high waves with overhanging crests; the sea looks white; heavy tumbling seas; poor visibility. |
| 11 | 56-63 | Violent storm | 37 ft (52 ft) | Exceptionally high waves; the sea is covered in foam patches; visibility badly reduced. |
| 12 | 64 and over | Hurricane | 45 ft and over | Air full of foam and spray; sea completely white; visibility very seriously reduced. |
Wind speeds and wave heights follow NWS Portland's chart. Heights are for the open ocean after the wind has blown long enough over a long fetch; sounds, straits and short fetches give much lower waves, while shoals, bars and opposing current make them steeper. NWS's Weather Prediction Center and the USCG boat crew handbook give height ranges instead (force 4: 3.5-5 ft; force 12: 52 ft and over). Some NWS pages call force 9 'severe gale'.
Sources (4)
weather.gov · wpc.ncep.noaa.gov · weather.gov · higherlogicdownload.s3.amazonaws.com
NWS marine advisories and warnings
| Product | Wind or sea criteria | Notes |
|---|---|---|
| Small Craft Advisory: Eastern Region (Maine to South Carolina, Lakes Erie and Ontario) | Sustained winds or frequent gusts of 25-33 kt (lower limit 20-25 kt in harbors, bays and lakes, set by area) and/or seas 4-7 ft or more (4 ft on Chesapeake Bay) | Varies by office. NWS Baltimore/Washington lists 18-33 kt or waves 4 ft or more for Chesapeake Bay and the Tidal Potomac. |
| Small Craft Advisory: Central Region (Great Lakes, Minnesota to Ohio) | 22-33 kt and/or waves over 4 ft | Region-wide range from the NWS directive; check your local office. |
| Small Craft Advisory: Southern Region (Georgia to Texas, Caribbean) | 20-33 kt and/or seas 7 ft or more expected for over 2 hours | Some offices also headline 'Small Craft Should Exercise Caution', e.g. Jacksonville for 15-20 kt or 6 ft seas (local criteria). |
| Small Craft Advisory: Western Region (Washington to California, including Puget Sound) | 21-33 kt and/or waves over 10 ft, or wave steepness past local limits | Also issued for rough bar conditions at coastal bars; the 'WHAT' line gives the cause. |
| Small Craft Advisory: Alaska | Sustained winds or frequent gusts of 23-33 kt; rough-seas advisory at locally set heights of at least 8 ft | Region-wide range from the NWS directive. |
| Small Craft Advisory: Pacific Region (Hawaii, Guam, American Samoa) | 25-33 kt and/or seas 10 ft or more; Guam and Northern Marianas 22-33 kt and/or 10 ft; American Samoa 20-33 kt and/or 8 ft | The weather.gov/marine/cwd page words the Hawaii criteria slightly differently. |
| Gale Warning | Sustained winds or frequent gusts of 34-47 kt | Same everywhere. Not tied to a tropical cyclone. |
| Storm Warning | 48-63 kt | Same everywhere. Not tied to a tropical cyclone. |
| Hurricane Force Wind Warning | 64 kt or more | Same everywhere. Used for strong storms that are not tropical cyclones. |
| Tropical Storm Warning | Sustained 34-63 kt expected within 36 hours | Tropical, subtropical or post-tropical cyclone; 24 hours in the western North Pacific. Tropical headlines override all others. |
| Hurricane Warning | Sustained 64 kt or more expected | Issued 36 hours before tropical-storm-force winds are expected (24 hours in the western North Pacific). |
| Special Marine Warning | Thunderstorm or squall winds or gusts of 34 kt or more, hail 3/4 inch or larger, or waterspouts; usually lasting 2 hours or less | Short-notice warning, also used for strong fronts and squall lines; placed on NOAA Weather Radio at once. |
| Hazardous Seas Warning | Wave height and/or steepness at or above locally set criteria | Criteria set by each office. |
| Dense Fog Advisory | Visibility down to a locally set limit of no more than 1 nm | Local limit varies. |
| Freezing Spray Advisory / Heavy Freezing Spray Warning | Ice building on a vessel at under 2 cm (0.8 in) per hour / 2 cm per hour or more (0.7 cm per hour in Alaska) | Cold-season hazard; ice weight up high reduces stability. |
| Watches (Gale, Storm, Hurricane Force Wind, Hazardous Seas) | Same thresholds as the matching warning | Risk is up, but timing or location is still uncertain. |
'Frequent gusts' means gusts lasting more than about 2 hours within a 12-hour forecast period. When a forecast range crosses a threshold, the higher category is used. Since December 2019 the separate Small Craft Advisories for winds, hazardous seas and rough bar are issued as one Small Craft Advisory. Region ranges come from NWS Instruction 10-303 (March 2025); the local office's own definitions govern its zones.
Sources (6)
weather.gov · weather.gov · weather.gov · weather.gov · weather.gov · weather.gov
Common sound signals (Rules 34 and 35)
| Situation | Signal | Rule |
|---|---|---|
| In sight, power-driven. International: 'I am altering course to starboard'. Inland (meeting or crossing within 1/2 mile): 'I intend to leave you on my port side' | 1 short | 34(a) |
| International: 'I am altering course to port'. Inland: 'I intend to leave you on my starboard side' | 2 short | 34(a) |
| Operating astern propulsion | 3 short | 34(a) |
| Inland: power-driven vessel intending to overtake on the other's starboard side / port side | 1 short / 2 short; the other vessel answers the same if it agrees | 34(c) Inland |
| International, narrow channel: 'I intend to overtake you on your starboard side' / 'on your port side' | 2 prolonged, 1 short / 2 prolonged, 2 short | 34(c) International |
| International, narrow channel: agreement to be overtaken | 1 prolonged, 1 short, 1 prolonged, 1 short | 34(c) International |
| Doubt or danger: you don't understand the other vessel's intentions or doubt it is doing enough | At least 5 short and rapid blasts | 34(d) |
| Nearing a bend or obstruction that could hide other vessels (answered by any vessel beyond it) | 1 prolonged | 34(e) |
| Inland: power-driven vessel leaving a dock or berth | 1 prolonged | 34(g) Inland |
| Restricted visibility: power-driven vessel making way | 1 prolonged, at least every 2 minutes | 35(a) |
| Restricted visibility: power-driven vessel underway but stopped | 2 prolonged about 2 seconds apart, at least every 2 minutes | 35(b) |
| Restricted visibility: sailing vessel, fishing, towing or pushing, not under command, or restricted in ability to maneuver (International also: constrained by draft) | 1 prolonged, 2 short, at least every 2 minutes | 35(c) |
| Restricted visibility: last vessel of a tow, if manned | 1 prolonged, 3 short, right after the towing vessel's signal if practicable | 35(e) |
| Restricted visibility: at anchor | Bell rung rapidly for about 5 seconds, at least every minute; may add 1 short, 1 prolonged, 1 short to warn an approaching vessel | 35(g) |
| Restricted visibility: fishing vessel at anchor, or vessel restricted in ability to maneuver working at anchor | 1 prolonged, 2 short instead of the anchor bell | 35(c) Inland; 35(d) International |
| Restricted visibility: aground | 3 separate bell strokes, rapid ringing, 3 separate strokes; may add a whistle signal | 35(h) |
| Restricted visibility: pilot vessel on duty (optional identity signal) | 4 short | 35(k) |
| Boats 12 m (39 ft) to under 20 m | Bell signals optional, but must make some other efficient sound signal at least every 2 minutes | 35(i) |
| Boats under 12 m | May use any efficient sound signal at least every 2 minutes instead of the signals above | 35(j) |
| Inland: boat under 20 m anchored in a Coast Guard special anchorage area | No anchor sound signal required | 35(l) Inland |
A short blast lasts about 1 second; a prolonged blast 4 to 6 seconds (Rule 32). Vessels of 12 m or more must carry a whistle, and 20 m or more a bell as well (Rule 33). Inland maneuvering signals state intentions and need an answer; International ones announce an action. Inland, agreement reached by VHF radio can replace the whistle signals (34(h)). Where International and Inland rules differ, check which applies where you are.
Sources (1)
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.