Landing through a Surf - BASIC, Because of the hazards of the sea, any seaman is likely to find it necessary to take almost any kind of ship's boat or raft ashore through a surf. He may have a green or exhausted crew whose lives as well as his own depend on his performance; it behooves every seaman to learn all he can of the subject both by study and actual experience whenever the opportunity offers.
A surf never looks as dangerous from seaward as it actually is, especially from a small boat. When there is any possibility of a surf, a beach should be approached with caution, and care should be taken to remain well outside the breakers until ready to make an attempt at running the surf. If there is any possibility of help from the shore, it should be awaited before running a heavy surf. If no help is available and it is necessary to run the surf unaided, two principles should be kept in mind. First, the boat must be kept end on to the surf to avoid broaching and capsizing. Second, the boat must be able to meet and resist the breakers to keep them from driving her toward the beach out of control or, in extreme cases, driving her under or throwing her end over end.
Methods of running the surf vary with the height of breakers, type of beach, set of current, weather, type and trim of boat, gear available, and experience and condition of crew. I will only mention methods considered safest and simplest here.
To understand the dangers in landing through surf, you should be familiar with the characteristics of surf. Surf is caused by winds, local or distant. The nature of the surf, depends on the character of the waves that approach the shore line and on the manner in which these waves are changed as they go from deep water into shallow water.
There are three main breaker types -
Plunging Type The back of the wave continues to be well rounded, but the front of the wave becomes so concave that the crest of the wave suddenly falls forward and breaks. This type of wave occurs mainly on beaches where the bottom has a steep slope.
Spilling Type Both sides of the wave grow more concave as the wave advances, until the wave is so steep and deep that it breaks down by spilling. This type usually occurs on flat beaches.
Surging Type This type usually occurs on steep beaches. It neither plunges nor spills but surges into a peak that it maintains up the beach face until it subsides.
In addition to the ratio of wave height to wave length, the beach slope, winds, currents, and the presence of an offshore bar will also influence breaker characteristics.
When waves run from deep into shallow water, the period, or time between successive crests, will not change to any extent. As the length and speed of the wave decreases, the height increases.
Studies show that a wave will break on a beach when the wave face slope becomes 90 degrees. This occurs at a depth of water between one and one and one-half times the height of the wave. However, the presence of a bar may cause the waves to break in deeper water. This would be indicated by a single line of breakers at high tide and by several diminishing lines at low tide.
Waves usually approach the shore at an angle. When they do, they break at an angle to the shore line, and a current is set up parallel to the beach. This longshore current is very treacherous when landing a boat through surf and is largely responsible for the tendency to broach. As the boat advances into the surf zone, the velocity of this longshore current increases as a result of three factors: increasing breaker height, increasing angle of the breaker with the beach, and steeper beach slopes. The velocity of the longshore current decreases with increasing wave period.
A rip current is a narrow seaward-moving water current that returns to deep water the water carried landward by waves. It can be very useful to the boat handler when approaching the beach because it tends to flatten the surf and allow for an easier passage.
