What constitutes heavy weather depends on the type and size of boat and the experience of the crew. In any given boat, the weather turns heavy when the winds increase 5 knots beyond anything previously experienced by the crew.
A powerboat in heavy weather is vulnerable because its high freeboard exposes a large surface area to the force of the wind and seas. Most powerboats also have large windows, which if broken can allow large quantities of water below. In heavy weather the powerboat’s options are limited to: running for cover, defensive course selection, or station keeping.
Running for cover
A powerboat’s main defense, especially the smaller boats, is speed and vigilance. The probability of successfully riding out a severe storm at sea is considerably less for a small powerboat than a small sailboat. The sooner a storm can be predicted the better chance the boat has to make it to safety. Boat speed places a limitation on how far a small powerboat can prudently get from sheltered conditions. In setting this limit, the skipper should be aware that a boat that can do 20 knots in flat water cannot do 20 knots once wind-generated waves are present, especially if the course is into those waves.
As the wind rises, a boat heading into the wind will have to reduce its speed or change its course to prevent pounding. If the waves are short and steep, the screws may come out of the water as well. Changing course so that the boat is running 45 degrees into the weather extends the boat’s path on the wave and reduces the pounding. This course is very uncomfortable due to the part roll and part pitch motion of the boat and lengthens the run for cover. Turning the boat downwind reduces the apparent wind on the boat by the speed of the boat and the motion is more comfortable. Downwind is the best direction to run for cover.
If the desired course of the boat places its beam to the seas, it may become necessary for the powerboat to tack towards its destination, running first 45 degrees into the wind then 135 degrees off the wind. It should be pointed out that the most vulnerable position for a boat in severe conditions is beam on to the wind and seas.
Defensive course selection
If it becomes necessary to ride out a storm in a powerboat, the major decision is whether to run into the waves or with them. The question of whether to run into or away from the storm is hotly contested and depends on the individual vessel, storm and skipper. Each skipper must judge the storm conditions and the behavior of the boat in choosing which course they think is best. The right choice early in a storm with steep, short seas may be different than later in the same storm when the seas lengthen and flatten.
Running downwind decreases the velocity of the wind by the speed of the boat and increases the length of the waves, which in turn reduces the forces the boat and crew must resist. For example, it is possible for a powerboat going 12 knots to run with a six- or seven-foot wave using the 2-knot orbital current on the crest to keep the boat on a single wave. This is not necessarily as good an idea as it sounds; because the boat will tend to surf down the wave front. When surfing, the water and the boat are moving at the same speed, helm control is reduced and the tendency to broach is increased. It is better to lose a little distance on the wave and regain helm control.
The general guidelines are that in short, steep seas it is best to slow the boat down and let the waves run under the boat. If the waves are high and long, hold as much speed as possible and run away from them.
Running downwind, the skipper should be mindful of the increased chance of pitchpoling, broaching or being pooped by a following sea, especially early in a storm. The seas are cycloidal in the early stages of a storm and their steep faces and sharp crests can cause considerable trouble. Negotiating short, steep seas safely requires the boat speed to be carefully controlled. The speed needs to be slow enough so the bow does not plunge into the trough or wave ahead causing the boat to be flipped by the wave coming from behind, yet fast enough to maintain steerage control and avoid broaching or being pooped by a following sea. Slowing a powerboat running downwind may not be an easy task. The wind force on the superstructure alone will drive it at surprisingly high speeds. Towing warps to slow a powerboat should be avoided. Any lines strung out behind a powerboat may become fouled on the prop with disastrous consequences.
Station keeping is very similar to heaving to with a sailboat. Enough power is maintained to keep the boat heading between 50 degrees off and directly into the wind. Just slightly off the wind is generally a little more comfortable where the motion is mostly pitch. The more off the wind the more power that can be applied, but the greater the danger of being caught by a gust and forcibly turned sideways to the wind and waves. In this position, the boat is very susceptible to broaching.
Holding the head into the wind by using a drogue, sea anchor or trailing warps off the bow may or may not work. According to the pre-eminent book on storm performance, Heavy Weather Sailing by Adlard Coles, the experience of sailboats using this method is poor. Certainly the sea anchor will keep the head into the seas and places the bow in a position to split the waves. However, the boat can no longer be powered forward with the engine or it will over run the lines. This is not a method to consider in a powerboat unless no other options are available.
If warps or sea anchors are to be set, it is best to attach them using a harness that is attached just aft of amidships rather than to the bow. Heavy loads on the bow will tend to depress it and increase the possibility of taking green water over the bow. The lines need to be protected from chafe and long enough to reach several wave lengths ahead of the boat. The amount of drag is important; the object is to slow and stabilize the boat, not to stop it. Too much drag will stop the boat and subject it to the full force of the breaking waves. The boat must be allowed to fall back with the wave so that the immense force of the wave will be dissipated and less damage will occur. This necessary backward movement places abnormal loads on the rudder and may damage it.
Changing course or removing warps in mid-storm is difficult. Recovering any warps in the midst of a storm is practically impossible and, if it becomes necessary, will probably require the warps to be cut loose. Radical course changes that require the vessel to pass beam to the weather are difficult and dangerous, especially if the crest of a wave hits the boat while it is beam to the weather. Try to make any turns beam to the weather on the backside of waves. It may not be possible to time the maneuver so that the boat can turn a full 180 degrees before the crest of the next wave hits, but breaking the turn into two segments may reduce the exposure. First, turn the boat 45 or 50 degrees off the wind and hold this course until a suitable sea approaches. Then, as the crest passes, make the remaining portion of the turn.
Don Dodds is the author of Modern Seamanship and Modern Cruising under Sail.