916 HYDROGRAPHIC MANUAL PaGE 830 



In regions where boulders, ledges, coral heads, or similar dangers probably exist, it is very desir- 

 able to mention that fact. Where boulders are common, a warning should be given that vessels should 

 avoid those places where the depth does not exceed the draft by so many feet. 



There is no need to list each one of a number of dangers in a locality. A description of the most 

 prominent, or possibly the one farthest offshore, with a general statement, will generally be sufficient. 

 (See Bars.) 



DANGERS, OUTLYING.— Describe and give Directions for clearing them. 



DATE OF A COAST PILOT. — A new edition of a Coast Pilot is given the date to which it is 

 corrected. This is usually the date of the latest Notice to Mariners used in correcting the proof. 

 This date is entered on the galley proof at the end of the preface. 



DATE OF INFORMATION. — Where information, such as depths in channels, or in docks, is 

 subject to change, the date of the soundings, or information given, is very important. Generally 

 both the month and year should be given, although the year alone is sufficient in some cases. (See 

 Channels.) 



DATUMS. — ^Refer depths and elevations to the same datums used on the charts of the 

 region. Explain this clearly and immistakably in the "Important" note (9135A(6)), and state what 

 the datums are, as mean low water, mean lower low water, mean high water, as the case may be. 

 Do not give the datums in the text, except for some special reason, as when some other datum is referred 

 to. Abbreviations for datums may be used, but must be in accordance with the Symbols and Abbre- 

 viations chart (fig. 189), e. g., MLW, MHW, etc. An explanation of these abbreviations should 

 be included in the "Important" note. 



DEFENSIVE SEA AREAS. — Define by general statement or reference to the chart, and give 

 the special regulations affecting navigation. These may be obtained from the Federal Register 

 and the Notices to Mariners. The regulations may be grouped in one place and referred to elsewhere 

 in the text. 



DEFINITIONS.— Refer to "A Glossary of Sea Terms," by G. Bradford, and to the "Port 

 Dictionary of Technical Terms," published by the American Association of Port Authorities. 



DELETE. — A term which is much used but whose meaning is not as clear to some as the term 

 "strike out." Use the latter in Supplements. 



DEPTH AND DRAFT. — In general, give depths; there are exceptions, but care must be used 

 in recommending channels for certain drafts, since it cannot be known what the condition of the 

 sea may be or how a vessel will handle. There may be a number of special conditions under which 

 & channel would not be safe for a draft that could be carried through it under ordinary conditions. 

 In some cases squat or list must be allowed for. In river channels the freshness of the water is some- 

 times a controlling factor. (See Channels.) 



DEPTH UNITS. — Use the same unit that is used on the specific chart being described, 

 but omit the datum. (See Datums.) Do not give meters, but include conversion tables in the 

 appendix. (See Meters.) 



DERATIZATION. — If certificates are required or issued, explain the conditions. If regulations 

 •concerning rat guards, etc., are effective, include whatever detail appears to be required. 



DETAIL. — Avoid including too much detail where not needed, as in channels that are well 

 marked, even if they are winding. This type of sailing direction may be best handled in some cases 

 by a simple statement to "follow the aids." 



Too much detail may be confusing and involves too many changeable features. It is often 

 impossible to keep such descriptions corrected in the Supplements. 



DIRECTIONS. — The field reviser should obtain all possible information about different routes, 

 established ranges, precautions that may be necessary on account of set of the current or lack of 

 turning room, whether local knowledge is necessary, and whether any unusual caution must be observed. 



Note all ranges or features that are of value in making courses good. 



In Chapter 3 of the Pilot, after the description of routes, such Directions are tabulated that 

 cover more than one chapter of the text (see 9135B(3)). Local Directions (those included within 

 any one chapter) for entering ports, etc., are given in place in the text with other information about 

 the place referred to. Local Directions may be given either in paragraph or tabular form, but the 

 latter should be avoided unless the Directions are of unusual length, since they cost more and usually 

 give less information. 



Local Directions should be headed, "Directions, ", the name of the port 



or route to which they apply being always included. Where Directions are in paragraph form, the 

 heading should be bold-faced as should all figures denoting courses. Important Directions, or those 



