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234 ity of building wooden boats of green timber to meet the present submarine emergency, the following data on the shrinkage of Douglas fir, from a pamphlet by Howard B. Oakleaf, United States forest service, Portland, Ore., are presented: ‘Douglas fir does not shrink much, and for this reason it is possible to use partially dried material in emer- gencies, without fear that the additional drying after the material has _ been shaped will open the seams or cause un- desirable stresses in the members. The following figures are given for the in- formation of those desiring to know the amount that Douglas fir will shrink under normal conditions from green to air dry: Radially, 1.52 per cent, tan- gentially, 2.37 per cent, and longitudi- nally, 0.0091 per cent.” Tables I and II THE MARINE REVIEW strength values for structural timbers, but in many cases the timbers have been unlike in grades and have varied materially in moisture content. Due to such variations, comparisons, in many cases have been very misleading. This point has been recognized in preparing the ac- companying data, and every effort was made to eliminate comparisons that were not on the same basis. All species of timber show varia- tions in weight and strength. These variations are considerable in some cases, depending on the quality of the clear wood, as well as on the grade and condition of seasoning of the tim- ber. It is essential that the quality of the timbers of any species be determined by due consideration of these factors, rather than locality of growth, etc. Table IV probably contains the best July, 191 weight of from 19 to 36 pounds per cubic foot, there is an accompanying increase in strength (modulus of rup- ture) of from 5500 to 10,500 pounds per square inch. These figures iridicate in. — creases of 47.2 and 47.7 per cent respec- tively for weight and strength, based — on the maximum values. In timbers — of structural sizes, however, such as are used in shipbuilding, this law does not — hold good on account of the influence of the knots on the strength. In such cases, the relation between dry weight and strength is erratic. A knowledge of timber grading is es- sential to the shipbuilder. Different — grading rules are used in different parts of the country, and detailed rule books may be procured from the _ various lumber associations. On the Pacific coast, the standard grade used at pres- State Washington Louisiana Mississippi North Carolina Texas Virginia Wisconsin California Florida Michigan Maine Georgia Pennsylvania South Carolina Tennessee Idaho Kentucky New Hampshire will be found to contain complete data on the strength of the principal Ameri- can woods used for shipbuilding and other structural purposes. While it is difficult to obtain correct comparisons of the strength properties of structural timbers, yet, from a practical point of view, the full structural sizes furnish the data sought by naval architects and shipbuilders to guide them in_ their designs. For Tables I and II we are in- debted to the West Coast Lumbermen’s association, Seattle, O. P. M. Goss, con- sulting engineer. In the preparation of the tables, showing the various proper- ties of structural timbers, every effort “was made to obtain the most reliable and up-to-date figures. In all com- parisons, consideration was given to the size of the timbers, general quality, moisture condition and other factors which affect the strength. Many pub- lications have presented data containing Ce eee oer ee oeeeeee eee ee ees eseoee CD Ce ee Oe eC CC ee eC ee Pe ee Ce ee ee ee Ce ee ee Ce ey Ce Cy were sewer eee e reese eto nees Ce ee et Pe ee Ce CeCe eee woes eee eet tees ereee Table III - Lumber Cut of the United States for 1915 by States From Data Compiled by the United States Forest Service No. of | Production mills in thousand active board feet State 440 3,950,000 News Worle ro, cies 500 3,900,000 OMG ae Seetaah s Cos 1,250 2,200,000 Miaissouti ea ek uck 8 2,900 2,000,000 Undiatia G82) sicacce we 500 1,850,000 Montana. ane 1,150 1,800,000 Vermont ........0+- 410 1,690,000 Massachusetts ...... 1,350 1,500,000 Oklahoma. 3.68.25 2,400 1,500,000 Maryland =< 33 sos .05. +6 600 1,300,000 WINOIS o asccsca eee 150 1,130,000 Connecticut ......... 400 1,110,000 Colorado siteiccccens 600 1,100,000 ATIZONA 22k Bisca cess 450 1,100,000 New Mexico ....... 950. 1,100,000 New Jersey ......... 900 1,000,000 FOWa vier cae hore eens 1,400 1,000,000 WOlA WATE Oc siccces a 1,900 950,00C South Dakota ...... 800 800,000 Wi OMINgs ccs ecu 1,800 800,000 Rhode Island ....... 210 777,000 tah eiieweaw ese ees 1,300 560,000 500 500,000 Totals? seas cece eres available data published in any gov- ernment bulletin covering the strength of different species of structural tim- ber, The data in this table are taken from United States forest service bulle- tin No. 108, page 65. This table shows the results of tests on a large number of stringers, similar to ship keelson timbers, of different species, graded by the tentative grading rule of the forest service. All the timbers were practi- cally of the same grade. The modulus of rupture of Douglas fir is given as 6919 pounds per square inch; the corre- sponding figure for long leaf pine is 6140 pounds per square inch. The dry weight of small, clear speci- mens, particularly for wood containing little or no resinous substance, is a definite indication of the strength of the wood fibre. This fact is shown for Douglas fir in. United States forest service bulletin No. 108, in which it is stated that with an increase in dry No. of | Production mills in thousand active board feet PoP ek Hace PL eRe eae 1,600 475,000 phiret ce eiery ee 850 400,000 REESE Ss REA on aO POR 850 350,000 Pear ERED AS PC SR eC 750 350,000 PEARS Ricur tr Amro rare tI. a 104 328,000 aa cete ie aie liveneaweosss sae 500 260,000 Meeps carsnaiewal ciara caer sterenets 400 250,000 ORES ec A TEECN BALE ARCO 225 230,000 SN iohinee nities men 400 165,000 Sie Ce wate eee ae 350 110,000 Melsleretd at gaene Gio shel 200 90,000 Dahie aia neesr eG uceoesein seat 144 79,500 BR eects aligtere fester as 14 75,915 SUA Se baae waa ce ae ack 43 65,787 Se nee 250 40,000 Gee racene eh oie lanes cleceiaceier eae 125 35,000 SN ar ee aca selec eS ace 75 25,000 SMO N ese gies eek ciewrats 29 23,800 Beeoel eat alee wievsial el tinie g 74 17,400 Bue pi eC ety W iaiac g natal che 25 15,000 See AOE OSES Cae 73 10,892 37,013,294 ent to secure high grade structural tim- bers is “Selected Common”. This grade covers timbers selected from the grade known as “No 1 Common”. No. 1 Common is described as follows: “This grade shall consist of lengths 8 feet and over (except shorter lengths as ordered) of a quality suitable for ordinary construc- tional purposes. Will allow a small amount of wane, large sound knots, large pitch pock- ets, colored sap one-third of the width and one-half the thickness, slight variation in saw- ing and slight streak of solid heart stain. Defects to be considered in connection with the size of the piece. Discoloration through exposure to the elements or: season checks not exceeding in length one-half the width of the piece, shall not be deemed a defect excluding lumber from this grade, if other- wise conforming to the grade of No. 1 Common.”’ From the foregoing specifications for No. 1 Common, the following specifica- tion for Selected Common, suitable for high class constructional purposes, in- cluding bridge timbers, floor joists, ship timbers, etc., designed to carry heavy