Bad Weather and Rough Water

By Captain Bob Figular, reprinted with permission from Mariner's Learning System

Entering or Exiting a Port

While operating your boat there will be times when you will need to either exit or enter a port in rough and challenging conditions. Although certain inlets and rivers have extreme conditions much more often than others, learning how rough weather affects the various harbours and entrances throughout your local area is necessary to operate safely. Knowing as much information as possible prior to entering a harbor, inlet, or river in rough weather will help guard against potential dangers or impending problems. In these cases local knowledge can make the difference between a safe passage or getting you and your crew in trouble. If you are operating in an area which is new or unfamiliar to you “local knowledge” can also be gained through the use of cruising guides or Coast Pilots found in many ship stores or online. Here are a few things you should be aware of before entering any of these areas:

1. Watch where waves break. Know how far out into the channel, whether near jetties or shoals, or directly across the entrance the waves break.
2. Pay close attention to how the entrance affects wave patterns. An entrance that has jetties may push waves back across an entrance where they combine with the original waves.
3. Some entrances have an outer bar that breaks, and then additional breaks farther in. Others are susceptible to a large, heaving motion that creates a heavy surge as it hits rocks or structures.
4. Know where the channel actually is. If shoaling has occurred, room to maneuver may be significantly reduced.
5. Know the actual depths of the water. Account for any difference between actual and charted depth due to water stage, height of tide, recent rainfall, or atmospheric pressure effects.

When entering a harbor, inlet, or river you will need to pay special attention to the direction of the current and seas. The most challenging condition you can encounter is when the current opposes the seas when operating near an entrance. In this case the current will have the effect of shortening the wavelength, and increasing the wave height. This makes waves much more unstable and closer together. While heading into the oncoming seas, you will find that the current is coming from behind your vessel thus pushing your boat into the seas at a relatively higher speed. You can reduce this effect (which will also give more time to react between waves) by slowing your vessel, although the current is coming from behind you will still need to keep enough headway to ensure effective steering. Do not to allow the current to push your boat into any large cresting waves or combined waves that are peaking together.

Transiting an Entrance

When transiting an entrance, you will find that maneuvering room is often very limited. The only safe water may be found in the area that you just left. Be ready to back down and avoid the breaking crest of a wave. This situation can become critical in following seas with a head current. The waves will overtake your vessel at a higher rate and will break more often. The current will reduce your boat’s speed over the ground (SOG) which will expose your vessel to more waves. In this condition it is important to remain calm and not panic. Remember that with all following seas, you need to stay on the back of the wave ahead. As these waves become unstable they tend to break more quickly, use extra caution to ensure that you do not go over the crest of the wave ahead. Concentrate both on the crest in front of you and the waves behind. You must keep a hand on the throttle and adjust your power continuously. In many entrances, there is not enough room to maneuver allowing you to take a breaking wave bow-on. Learn to understand and anticipate the flow and direction of the waves. If a wave looks like it is going to break, your only out may be to back down before the wave gets to the vessel. Stay extremely aware of any wave combinations and avoid spots ahead where they tend to peak. If they peak ahead in the same place, chances are they will peak there when you and your vessel are closer. Do not let a slightly different wave or wave combination catch you by surprise!

In a situation when the current and seas are going in the same direction, current has the effect of lengthening the waves. Longer waves are more stable, with the crests farther apart, with this said you still need to use caution.

While heading into the seas and current, your boats forward speed over the ground (SOG) will be lessened, this in turn will require more time transiting the entrance. Increasing your boat speed may be necessary to maintain forward progress. However, do not increase your boat speed to a point that makes negotiating the waves hazardous. If you have increased your overall boat speed to maintain forward progress you will need to reduce the boats speed as you approach each wave crest individually to maintain control.

With following seas and current, your speed over the ground will be increased. Because the waves are farther apart, the effort required to ride the back of the wave ahead should be easier. Because the current is coming from behind your vessel, more forward way will be required to maintain steering control. As with all following seas, stay on the back of the wave ahead. Do not allow yourself to be lulled into a false sense of security. With higher speed over the ground and less maneuverability due to the following current, there is not as much time to avoid a situation ahead. Keep a hand on the throttle and adjust power continuously. Because less time will be spent in the entrance, stay extremely aware of any spots ahead to avoid. Maneuver early, as the current will carry the boat.

Dealing with High Winds

In addition to coping with the current and state of the seas it is also necessary to understand how to deal with high winds and the effects they will have on your boat when transiting harbours, inlets, or rivers. Depending on your vessels design and sail area, it may be necessary to steadily apply helm to hold a course in high winds. As a boat operator you should be able to “read” the water to identify stronger gusts. The amount of chop on the surface will increase in gusts, and extremely powerful gusts may even blow the tops off waves. The effect of a gust should be anticipated before it hits your boat. In large waves, the wave crest will block much of the wind when the boat is in the trough. Plan to offset its full force at the crest of the wave. The force of the wind may accentuate a breaking crest, and require steering into the wind when near the crest in head seas. Depending on the vessel, winds may force the bow off to one side while crossing the crest. For light vessels, the force of the wind at the wave crest could easily get under the bow sections (or sponson on a RIB), lift the bow to an unsafe angle, or force it sideways. Though a light vessel must keep some speed to get over or through the crest of a large wave, do not use so much speed that the vessel clears the crest, most of the bottom is exposed to a high wind. Be particularly cautious in gusty conditions and stay ready for a sudden large gust when clearing a wave. If your boat is fitted with twin-engines, be ready to use asymmetric propulsion to get the bow into or through the wind. As with all other maneuvers, early and steady application of power is much more effective than a “catch-up” burst of power. Vessels with large sail area and superstructures will develop an almost constant heel during high winds. In a gust, sudden heel, at times becoming extreme, may develop. This could cause handling difficulties at the crest of high waves. If the vessel exhibits theses tendencies, exercise extreme caution when cresting waves. Learn to safely balance available power and steering against the effects of winds and waves.

By following these simple procedures and considerations when transiting harbours, inlets, or rivers you be ready to handle even the toughest challenging conditions.