• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
Littoral  Current
Figure 6-10.-Sample surf worksheet.

Aerographers Mate 1 & C
Page Navigation
  123    124    125    126    127  128  129    130    131    132    133  
. 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 refraction  occurs. . Longshore current - current parallel to beach due to breaker angle, height, period, and beach slope. OBJECTIVE TECHNIQUE FOR FORECASTING SURF 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 the  worksheet. 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  Aerographer’s 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 INDEX 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, COMNAVSURFPAC/COMNAVSURFLANTINST 3840.1.  By  following  the  listed  procedures  on  the Modified   Surf   Index   Calculation   Sheet   the Aerographer’s  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 breaker height. For more information on amphibious operations, see Environmental Effects on Weapon’s Systems and Naval Warfare (U),  (S)RP1. FORECASTING  SURFACE CURRENTS LEARNING   OBJECTIVES:   Distinguish between tidal and nontidal currents. Define the terms  associated  with  currents. Classify 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 6-15







Western Governors University

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.