Planning to go to your desired area by boat can be a stressful situation at first. Some sailors use their previous sailing trips as benchmarks to determine the optimal time to leave the docks. But if you haven’t made this particular type of sailing trip before, past experience may not be a great guide. Instead of using past boating experiences to predict the approximate arrival times, we can use a simple calculation to help you estimate approximately how long to sail 100 miles.
Of course, we can only get a rough estimate from this number, as a variety of other factors such as weather conditions, wind speed, obstacles, etc. will play into the final result.
But let’s start with the basics.
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How Long to Sail 100 Miles?
Here’s a scenario.
Let’s say you want to sail to an island 100 nautical miles (nm) away. The trip will be in open water with reasonably favorable wind and water conditions.
You figure you’ll be traveling at a speed of 8 miles an hour. And with the traditional D = S x T formula, you can calculate how long it takes to sail 100 miles. Here are all of the variations of this equation.
Time, Distance, and Speed Equation Variations
- T (Time) = D (Distance)/ S (Speed)
- S (Speed) = D (Distance)/ T (Time)
- D (Distance) = S (Speed) x T (Time)
Measurement Conversions
And when determining the time, you have to remember that it’s not the same as calculating your distance. However, if we calculate the time using mph alone, you’ll have an inaccurate result and arrival time.
Instead, we have to convert the mph into knots. Since you’re sailing, you’ll want to use the knots measurement as it determines nautical miles per hour.
- 1 mph = 0.868976 knots (kts)
- The island is 100 nautical miles away.
- The boat is cruising at a speed of 8 mph.
So let’s convert the 8 mph into knots.
- 30 x 0.868976 = 6.9 knots.
Let’s round it up to 7 knots. That’s a pretty aggressive speed for an average-sized boat with a typical displacement-style hull.
So How Do We Calculate the Time?
Now that we have the Distance (100 nm), and the boat’s speed (7 knots), you can use the previous formula to find the time. While there are many factors in determining the speed of your boat (i.e., wind speed, weather, boat size, etc.), we’ll explain those later.
Moving forward, this is how you can calculate how long it takes to sail 100 nm.
Time = Distance/Speed
- Time = 100 mph / 7 kts
- Time = 14.2 hours
Based on this equation, it will take you about 14.2 hours moving at an average speed to reach the island goal a far 100 nm away.
However, that’s just the basics. Weather and other factors will play a role. Here’s how to consider some additional factors.
Weather, Speed, and Distance
The weather is one of the main factors you’ll have to consider when putting together your sailing plans. Summer warmth brings along with it an increase in opportunity but along with it more varied weather. Being proactive with how you track day to day or hour to hour weather reports will allow you to prepare for any variable that will impact your overall plans.
We suggest that you monitor the marine forecast for the most accurate details specific to your intended trip. Out on the water, the weather can change quickly, leaving you dealing with delays, harsher weather than expected, or worse.
If the forecasts note that there is heavy rain or unpredictable surges, it’s best to save your sailing trip for another day.
How to Prepare for Adverse Weather
From rapidly changing clouds and wind directions to severe hurricanes, boaters can experience a myriad of weather threats while sailing.
Thunderstorms are a more common threat to sailors because they can develop quickly, especially in warmer climates.
According to both the National Weather Service and the Coast Guard, sailors should not venture out if there is a possible chance of thunderstorms. If you’re sailing in open water and notice an approaching storm, it is best to return to shore immediately or attempt to avoid the storm.
If you’re unable to return to shore, you should “stay inside your cabin and avoid touching any electrical or metal devices.” If your vessel doesn’t have a cabin, then remain as low as possible. Here are some signs that the weather is changing:
- A sudden increase or decrease in temperature
- A sudden shift in wind direction or increased wind speed
- Horizon flashes
- Flat clouds are becoming thicker and lower
- Static AM on your radio, which can be a sign of early thunderstorms.
Wind Speed & Waves
When the wind starts to push more powerfully across the water, at first, there are subtle effects that occur. It creates slightly ripples, which are visible when observing the surface.
However, the wavelet movements are slower than the wind, and the pushing wind will increase the size of the ripples until they are steep enough to break. This wavelet movement occurs when the wind reaches a three on the Beaufort scale.
As the wind size increases, the number of breaking waves and waves will increase.
Average Wind Speed and the Beaufort Scale
So what is the Beaufort scale?
The Beaufort scale is a set of measurements that relates to wind speed that can be observed on land or sea. Here is a table that shows the Beaufort Scale.
| Wind Force | Description | km/h | mph | knots | Specs |
|---|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <1 | Smoke will rise vertically in air |
| 1 | Minimal Air | 1-5 | 1-3 | 1-3 | Ripples will appear, but no foam crests are present. |
| 2 | Light Breeze | 6-11 | 4-7 | 4-6 | Small, short wavelets are formed. The crests give a glassy appearance and don’t break. |
| 3 | Gentle Breeze | 12-19 | 8-12 | 7-10 | Large wavelets are formed while crests start to break. |
| 4 | Moderate | 20-28 | 13-18 | 11-16 | Small, but longer waves start to appear. |
| 5 | Fresh Breeze | 29-38 | 19-24 | 17-21 | Moderate waves with small chances of sprays occurring. |
| 6 | Strong Breeze | 38-49 | 25-31 | 22-27 | Large waves start to form, with a small chance of spray. |
| 7 | Near Gale | 50-61 | 32-38 | 28-33 | Moderately high waves. The foam is blown in streaks based on the wind direction. |
| 8 | Gale | 62-74 | 39-46 | 34-40 | Moderate waves with more length |
| 9 | Strong Gale | 75-88 | 47-54 | 41-47 | High waves. Dense streaks of foam start to appear. |
| 10 | Storm | 89-102 | 55-63 | 48-55 | Very high waves with low hanging crests. The surface of the sea begins to take a white appearance. |
| 11 | Violent Storm | 103-117 | 64-72 | 56-63 | The sea is fully covered with white foam patches on the wind’s direction. |
| 12 | Hurricane | 118+ | 73+ | 64+ | The area is filled with spray and foam, and the visibility is highly affected. |
Note: These are mean speeds, meaning that they are averaged via convention, and don’t account for the wind gust speeds.
With the Beaufort scale, it’s easy to look at the sea and determine if it’s safe to travel. As a rule of thumb, we suggest that you plan your 100-mile trip if it’s at a 1-6 on the Beaufort scale.
However, there will be times when the seas are unpredictable. If you’re sailing and experience sea current at a 7-12 on the Beaufort scale, you should try to get back to shore, or move out of the band of nasty weather.
Under no circumstances should you sail at a 10-12, as chances are you’ll capsize your ship, placing you and your passengers at risk.
Coastline vs. Open Water
Coastline water is where the land is connected to the ocean or a line that creates a boundary between the land and the lake or sea. If you’re sailing along the coastline, you have a better chance of getting back to shore safely if an emergency arises.
Coastline Travel
If you’re sailing along a coastline, you’ll have to be much more aware of objects that might be in your way, no-travel zones, sandbars, and other potential obstacles that will require you to route your boat around them.
If you need to add distance to your travel to avoid obstacles or certain areas, of course, this will increase your overall distance, and therefore overall travel time.
Open Water Travel
There are far fewer worries in terms of objects, obstacles, and no-go zones when traveling in open water. But of course, open water creates its own set of concerns.
The further you are from shore, the more cautious you have to be about safety. If your ship capsizes 50 nm into your 100-mile journey, you’re going to need to stay alert and calm to come back to shore, which is why having emergency notification equipment and a flare gun on hand is an absolute necessity.
No matter where you are planning to sail, always tell someone where and when you’re going. This will help if an emergency arises and you are unable to contact anyone.
Boat Size and Hull Type
Often larger sailboats will be able to travel at faster speeds than smaller boats, due to the size of the hull. The more hull area that is in contact with the water, the less drag. This will translate into a faster maximum speed. It is often assumed that the more hull you have in the water, the more drag there will be, but this is not the case.
Of course, this won’t be true of certain hull types like catamarans, trimarans, and other hulls that don’t displace water. These boat hulls don’t work under the same physical properties as traditional displacement hulls.
Improve Sailing has an excellent article that goes over the theoretical maximum speeds of various hull types.
Conclusion
Depending on the size of your boat and the maximum cruising speed, a 100 nm sailing journey typically takes in the range of 10-16 hours. Using the calculations shown above, you can adjust how far you’re going, and the conditions, and get a rough idea of your timing.
Plan for all possibilities as the weather can change at any moment. Through understanding marine weather forecasting, the size of your boat, and other factors, you’ll be reaching that island party at no time.
Sources:
https://improvesailing.com/questions/average-sailboat-speed
https://www.jetdock.com/knowledge-center/how-to-calculate-travel-time-&-distance-by-boat.asp
https://www.sailmagazine.com/cruising/coastal-cruising-101
http://weather.mailasail.com/Franks-Weather/How-To-Use-Marine-Weather-Forecasts
