. Wave steepness index - ratio of the deep water
wave height to deep water wave period squared
l Breaker height index - ratio of breaker height to
deep water wave height.
. Breaker type - classification of breaker as to
spilling, plunging, or surging.
. Breaker depth index - ratio of depth of breaking
to deep water wave height.
. Width of surf zone - horizontal distance in yards
between the outermost breakers and the limit of wave
uprush on the beach.
. Refraction index - ratio of depth of breaking to
the deep water wave length.
l Coefficient of refraction - percent of breaker
height that will actually be seen on the beach after
. Longshore current - current parallel to beach due
to breaker angle, height, period, and beach slope.
OBJECTIVE TECHNIQUE FOR
Figure 6-10 provides an example of the surf
worksheet that may be used in a surf forecasting
procedure. The steps in the method conform to steps on
Equipped with an understanding of the terms
discussed above, the surf forecast worksheet, figure
6-10, and the step-by-step procedures listed in Surf
Forecasting, NAVEDTRA 40570, the Aerographers
Mate can prepare accurate surf forecasts.
The presentation to the user can be made in any
manner that is agreed upon; however, figure 6-11
illustrates one of the most commonly used methods.
FORECASTING THE MODIFIED SURF
The Modified Surf Index is a dimensionless number
that provides a measure of likely conditions to be
encountered in the surf zone. The Modified Surf Index
provides a guide for judging the feasibility of landing
operations for various types of landing craft.
The Modified Surf Index Calculation Sheet,
breaker, period, and wave angle modification tables
are listed in the J o i n t S u f f M a n u a l,
3840.1. By following the listed procedures on the
Modified Surf Index Calculation Sheet the
Aerographers mate obtains an objective tool to be used
by on-scene commanders.
The Joint Surf Manual also lists modified surf limits
for various propeller driven landing craft. The modified
surf index is not applicable for the Landing Craft Air
Cushion (LCAC). LCAC operations use the significant
For more information on amphibious operations,
see Environmental Effects on Weapons Systems and
Naval Warfare (U), (S)RP1.
LEARNING OBJECTIVES: Distinguish
between tidal and nontidal currents. Define the
terms associated with currents.
currents as wind driven, coastal, or tidal.
Identify publications available to obtain tidal
and current information.
Although the forecasting of surface currents has
been performed by aerographers for a number of years,
the prominence of such forecasting became more
evident when a number of incidents involving large
sea-going oil tankers occurred. Collisions and
grounding involving tankers caused great amounts of
pollutants, mainly oil, to be spilled on the water surface.
The movement, both direction and speed, of such
contaminants is directly controlled by the surface
currents in the affected area. More concerned emphasis
has now been placed on the ability of forecasters to
predict the movement of such contaminated areas.
In the past, NAVMETOC units have provided
forecasts to assist in the location of personnel or boats
adrift in the open sea as well as forecasts used in
estimating ice flow.
With the growing concern about pollution and
contamination of ocean waters, it is anticipated that
more requests for current and drift forecasts will be
directed to NAVMETOC units.
In this section, we will discuss the general
characteristics of currents, how they form, and the
different types of currents. There are presently no hard
and fast rules or techniques that are universally