HARMONIC PREDICTION . Method of predicting tides 

 and tidal currents by combining the harmonic con- 

 stituents into a single tide curve. The work is 

 usually done mechanically by means of a machine 

 designed for the purpose. (14) 



HARMONIC TIDE PLANE . See INDIAN SPRING LOW WATER. 



HARPOON LOG . A log which consists essentially of 

 a rotator and distance registering device combined 

 in a single unit, which is towed through the water. 

 It has been largely replaced by the taffrail log, 

 which is similar except that the registering device 

 is located at the taffrail, with only the rotator 

 in the water. (17) 



HAULAGE ROPE. See WIRE ROPE. 



HAWSER. See WIRE ROPE. 



HAYCOCK . An isolated ice cone rising above the 

 surface of LAND ICE or SHELF ICE as a result of 

 pressure or ice movement, (25) 



HEAD SEA . A sea in which the waves move in a 

 direction approximately opposite to the heading. 

 The opposite is FOLLOWING SEA. Those moving in a 

 direction approximately 90° from the heading are 

 called BEAM SEA, and those moving in a direction 

 approximately 45° from the heading (striking the 

 quarter) are called QUARTERING SEA. See CROSS SEA. 

 (17) 



HEADLAND . A point or portion of land jutting out 

 into the sea, a lake, or other body of water; a 

 CAPE or PROMONTORY; now, usually specifically, a 

 promontory especially bold and cliff-like. (11) 



HEAVE . 1. The motion imparted to a floating body 

 by wave action. It includes both the vertical 

 rise and fall, and the horizontal transport. 



2. The up and down motion of the center 

 of gravity of a ship. (12) 



HEAVY FLOE. A FLOE that is more than 10 feet thick. 



(25) 



HEAVY ICE . Any SEA ICE more than 10 feet thick. 

 (25) 



HETERODYNE . The action between two alternating 

 currents of different frequencies in the same 

 circuit; they are alternately additive and sub- 

 tractive, thus producing two beat frequencies which 

 are the sum of, and difference between, the two 

 original frequencies. (20) 



HI-FIX DECCA . Hi-Fix is a short range navigational 

 survey system which uses the 2 to 3 megacycle band. 



Some of the outstanding features of the Hi- 

 Fix system are: 



It uses one frequency. If lane identification 

 is desired, then a second frequency is needed, 

 which does not have to be harmonically related to 

 the first. 



The signals are not modulated, and therefore 

 give very little interference to other services. 



The system can be arranged either as a two- 

 range (for single party operation) or hyperbolic 

 (for unlimited parties), without any additional 

 equipment. If the Master is placed on the ship, 

 it becomes a two-range system. 



Regardless of what frequency is used, the lane 

 width in a two-range system remains fixed. Any 

 prearranged unit (feet, yards, or meters) may be 

 chosen. This is important as all boat sheets can 

 be prepared with the same lane widths regardless 

 of frequencies. 



If the ground stations are duplicated at 

 separate frequencies the system is then capable of 

 lane identification. The duplicate systems may be 

 run simultaneously and fixes can be had from both 

 systems to check one against the other. This 



guards against the failure of one system. There 

 are no signals transmitted between ground stations. 

 Ground stations can be located without regard to 

 the lane in between the two stations. (29) 



HIGH-PASS FILTER . A high-pass filter is a wave 

 filter having a single transmission band extend- 

 ing from some critical or cutoff frequency, not 

 zero, up to very large or infinite frequencies. (9) 



HIGH TIDE . See HIGH WATER. 



HIGH WATER (HW) (HIGH TIDE) ■ The maximum height 

 reached by a rising tide. The height may be due 

 solely to the periodic tidal forces or it may have 

 superimposed upon it the effects of prevailing 

 meteorological conditions. (14) 



HIGH WATER LINE . In strictness, the intersection 

 of the plane of mean high water with the shore. 

 The shore line delineated on the nautical charts 

 of the Coast and Geodetic Survey is an approxima- 

 tion to the high water line. (14) 



HIGH WATER OF ORDINARY SPRING TIDES (HWOST) . A 

 tidal datum appearing in some British publications, 

 based on high water of ordinary spring tides. (11) 



HIGHER HIGH WATER (HHW) . The higher of the two 

 high waters of any tidal day. The single high 

 water occurring daily during periods when the tide 

 is diurnal is considered to be a higher high water. 

 (14) 



HIGHER LOW WATER (HLW) . The higher of the two low 

 waters of any tidal day. (14) 



HINDCASTING, WAVE . The calculation from historic 

 synoptic wind charts of the wave characteristics 

 that probably occurred at some past time. (11) 



HINTERLAND . The region inland from the coast. (11) 



HIRAN. See SHORAN. 



HMMFC . House Merchant Marine and Fisheries Com- 

 mittee -- Subcommittee on Oceanography. 



HO. Hydrographic Office. (Now officially de- 

 signated U.S. Naval Oceanographic Office) 



HODOGRAPH. In general (mathematics), the locus of 

 one end of a variable vector as the other end re- 

 mains fixed. A common hodograph in meteorology 

 represents the vertical distribution of the hori- 

 zontal wind. (12) 



HODS . Hydrographic Oceanographic Data Sheets. 



HOLDFAST. (1) Flattened disklike tip of a tendril, 

 used in attachment; (2) basal part of an algal 

 THALLUS , which attaches it to a solid object; may 

 be unicellular or composed of a mass of tissue. 

 (18) 



HOLDING GROUND . The condition of the bottom of an 

 anchorage area; called good or bad according to 

 whether or not the material of which the bottom 

 is composed will prevent a ship's anchor from 

 dragging. (27) 



HOLME SUCTION GRAB . In this device the force 

 required to suck in a sample of the sediment is 

 provided by a 'Vacuum" chamber (containing air at 

 atmospheric pressure) which is mounted above the 

 collecting tube. On striking the bottom the cham- 

 ber is put into communication with the outside and 

 the water pressure forces the sample into the col- 

 lecting tube. The pressure chamber itself is a 

 strong brass tube closed at the upper end by a 

 lid and held firmly in position by a clamp. A 

 sampling tube is fixed below the chamber and ex- 

 tends upwards into it. Between the upper and 



56 



