Captain Bill discusses the Beaufort Scale, how to analyze wind and waves in bad weather, and how to adjust your driving according to the storm’s intensity
When it comes to driving a boat in rough water, every person has a different comfort zone. Some people I know want the water to be dead calm before they will go boating, while others seem to enjoy riding in challenging waves. Combine this reality with the fact that almost every boating location presents different water conditions and you can see that the definition of what constitutes “rough water” varies dramatically.
Because of this, the best way for me to provide useful information on how to be safe and comfortable in rough water is to look separately at the different water conditions and wind speeds that you will encounter. Some driving procedures will be the same for all rough water conditions, while some will come into play as water becomes more turbulent. The universal definition for what type of water is produced by different wind speeds is the Beaufort Scale, so I will use its water descriptions for different levels and suggest the steps you should take for each one.
Rough water begins with wind. Okay, sometimes it can be an under sea volcano and sometimes rip tides, but lets just limit this article to the sort of nasty water that we are most likely to encounter in our boating lifetime. Energy is transferred from the wind to the water’s surface by friction. It figures, therefore, that the greater the distance that a wind has the opportunity to stir up a water surface, the choppier the water surface will become. The distance for which a wind can affect the water surface is called “reach.” The greater the reach, the choppier the water. That is precisely why you never see ocean swells on a small lake.
When the wind is less than 8 mph, there is generally little cause for concern. You may encounter what are called ‘wavelets,’ but even boats under 20 feet will travel comfortably across such water. Once the wind exceeds 8 mph, however, you will notice a significant difference in the water surface. As winds exceed 15 mph, wavelets become small waves and you will see the waves growing and becoming more frequent, with some demonstrating breaking crests. This is the point where a different driving technique is necessary.
The first step is to head directly into the waves and adjust your throttle setting until you find a speed that provides a comfortable ride. Once this speed is found, turn slightly to your desired heading and add a little throttle to bring your boat speed up to the point where you are coming into the waves with the same frequency that you did when you had a soft ride heading straight into them. Boats over 28 feet will ‘bridge’ the waves at this level and the ride will be acceptable with little change to your driving procedure. Boats 28 feet and under will have more difficulty when maneuvering in canals and marinas. The solution here is to stay ahead of the problem by constantly anticipating wind effect and maneuvering accordingly.
Winds 19 to 24 mph are number 5 on the Beaufort Scale. Waves are more pronounced and longer with some white caps that can project spray into boats under 28 feet. At this Beaufort level, some passengers will raise objections, more from concern that the weather will get worse than from any serious discomfort with the existing ride. Nonetheless, if your boat is less than 35 feet, you should consider the possibility of further weather deterioration and plan how you will handle things if it does. Speedy travel times cease to be a priority and you should move your throttle to different speed settings until you find the speed that minimizes the pounding. If you are more than a few minutes from your destination, you should break out the life jackets and have them at the ready.
When the wind is between 25 and 38 mph (that’s number 6 and 7 on the Beaufort Scale), things will become uncomfortable for everyone onboard. A weather advisory called a “Small Craft Advisory” is issued. While Coast Guard waffles on exactly what boat length constitutes a small craft, there is general agreement that the warning applies to any boat under 65 feet. With wind speeds in this category, waves are significant and they can have white caps that produce spray. Water will be seen blowing in streaks along the direction of the wind. As you motor through wave troughs, some water will spill into smaller boats. Any boat under 40 feet can expect some sharp thumps when coming off waves. As a captain, you should tell everyone onboard to don a life jacket, even just as a precaution. Driving will require far more regular adjustments of motor trim and/or stern trim-tabs to keep you in smoother rhythm with the waves. Through experimentation, find a direction as well as a throttle setting that reduces the negative wave effect. Remember that when heading downwind, you should add UP trim and don’t allow the waves to overtake you. This reduces the chance of broaching. When heading upwind add DOWN trim, reducing the chance of doing ‘air time’ over a wave only to stuff the bow into the following wave.
When the winds exceed 39 mph, your driving objective must change from arriving at your original destination to locating the nearest safe moorage and setting a new heading in that direction. Look for a protected bay or the lee side of a larger land mass where the wind speed will not be as strong. Crests of waves will begin to topple and holding a desired course will become difficult. Pay close attention to your boat’s position relative to the direction of the waves, and try to hit the oncoming waves head on if possible. You don’t want to allow a large wave to catch you broadside. Winds of this category will make things difficult for even large yachts and for small pleasure boats it represents a serious concern. When you decide to retreat to a refuge bay or land mass, be aware that as waves reach shallower water near shore they convert to steep waves These reflected waves can produce a multi-directional chop that interferes with maneuvering into what you thought was a “safe” bay. If you have experienced winds in this category, you will be surprised to learn that there are still four higher wind levels on the Beaufort Scale. Don’t go there.
Whatever your status, if you feel genuinely threatened do not hesitate to radio a “Pan” to Coast Guard and other boats in your vicinity (but remember that once you are safe, you must broadcast a cancellation for your Pan in order for the Coast Guard to stand down). To feel more confident driving in poor conditions, compare your actual on water situation to the above descriptions and then follow the matching instructions.
Of course the best way to handle all nasty water is to avoid it. As the expression goes, “an ounce of prevention is worth a pound of cure.” Before making a firm commitment to go boating, get in the habit of checking the local weather, paying special attention to wind speeds and direction. This is simple logic. If wind is forecast and you decide to proceed, pack rain and head gear, protective glasses, towels and waterproof charts. And be sure you have a working life vest for everyone on board.
Of all the challenges you will face as a boater, handling your boat in bad weather conditions may be the most difficult. You are likely reading this article to see if you can learn some new tips for driving your boat on that dreaded day when you find yourself trapped in rough water and serious waves. Perhaps reading this article a few times will help.
You might also like:
QuickTips – Navigating Bad Weather
QuickTips – What to Consider Before Heading Out in Bad Weather
QuickTips – Boating in Waves
Understanding Marine Weather Forecasts and Isolated vs. Scattered Storms