Safe wind speed for boating: what the number does not tell you

"What wind speed is safe for boating?" has no single answer, and anyone who gives you one number is selling simplicity. The honest version is that the wind speed matters less than four other things: your boat, your experience, the direction the wind is coming from, and whether it is building or easing.

Rough working ranges

For a small powerboat under about 25 feet, with a competent but not expert skipper:

• 0-10 knots — comfortable for everybody, including first-timers.
• 10-15 knots — pleasant with some chop. Fine for most, spray on the way upwind.
• 15-20 knots — getting real. Manageable with experience; not the day to take guests who have never been on a boat.
• 20-25 knots — demanding. Slow going upwind, wet, tiring, and docking becomes the hardest part of the day.
• Over 25 knots — small craft stay home. This is where a Small Craft Advisory typically sits, and it is a warning issued by people who know the local water.

Sailors read these numbers differently: 15-20 knots is often the best sailing of the year, and the relevant question is when to reef rather than whether to go.

The four things that matter more than the number

Gusts. Gusts routinely exceed the sustained wind by 30-40 percent. A forecast of 18 knots gusting 28 is a 28-knot day, because the gust is what hits you when you are half-way into a slip.

Direction, relative to your route and your harbour. An offshore wind flattens the water near the beach and feels deceptively gentle — while it is quietly pushing you away from land. An onshore wind builds a lee shore and makes the harbour entrance the most dangerous point of the trip.

Fetch. The same 20 knots across a mile of protected bay and across fifty miles of open water produce completely different seas. Fetch, not wind speed, builds waves.

Wind against current or tide. When wind opposes a moving body of water, waves stack up short and steep. This is why some inlets are dangerous in conditions that look mild everywhere else.

The question that replaces the number

Instead of "is 18 knots safe?", ask four questions:

1. Is it building or easing? Going out in a dying breeze is nothing like going out ahead of a front.
2. What will it be when I come back? Sea breeze peaks in the afternoon on most coasts; the return leg is usually the harder one.
3. Where is my shelter? Knowing the bay or harbour you can duck into, and how far it is, changes what risk is acceptable.
4. Who is on board? The boat's limit is usually well beyond the crew's. Children, guests and anyone prone to seasickness lower the threshold considerably.

One rule worth keeping

Decide before you leave the dock and write the decision down as a condition: "we turn back if it hits 20, or by 4 pm, whichever comes first." Decisions made in advance, on land, are far better than decisions made two hours later while wet, tired and reluctant to admit the day is over.

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