47 



der forøvrigt er lukket, kommer omtrent 0. m 5 (20 Tommer) 

 under Skibsbunden og visende ret forefter. Denne Afstand 

 fandt vi var den hensigtsmæssigste. En mindre Afstand 

 bragte Hullet for mer det af Skibsbunden medslæbte Vand, 

 en større Afstand rønnede for meget paa det fritstaaende 

 Rør under større Fart. Pakningsskruen c tilskrues. Oven- 

 for c bor Koret a have en mindre Kran d. Fra a's ovre 

 Ende gaar et tyndt Blyrør til Stigerøret g, der har omtrenl 

 10"" (4 Tommers) Diameter. Hette maa placeres midt- 

 skibs. vertikalt og saa lavt. at dets nedre Ende er godl 

 under laveste (nederste) Vandlinies Plan. Det er forsynet 

 med Blænde, for at ikke Våndet under Skibets Bevægelse 

 skal pumpe i Roret. I dette Stigerør er anbragt en Fly- 

 der, fra hvilken der gaar en Snor over en Metalrulle paa 

 Toppen af Røret, derfra over en anden Rulle paa Toppen 

 af Skalaen, og Tampen er stukket gjennem et lidet Blylod, 

 der vandrer mellem to tynde Messingstænger langs Skalaen, 

 og som fæstes til Snoren ved at man trykker ind en liden 

 Trækile nedenfra i det Hul. gjennem hvilket Snoren er 

 trukket. 



Under Skibets Fart forover trykkes Våndet op i Stige- 

 røret, og ettersom Flyderen kommer hojere. synker Loddet 

 langs Skalaen. Saasnart Farten er bleven jevn. staar Lod- 

 det uforandret paa samme Højde paa Skalaen, hvor Fartens 

 Størrelse da kan afkeses i et Øjeblik. 



Vandloggen er. som man ser. en speciel Anvendelse 

 at 1'itofs Rør. Kaldes den Højde, hvortil Våndet stiger i 

 Stigerøret over det Niveau, det indtager, naar Fartøjet 

 ligger stille. //. Skillets Hastighed r. Tyngdens Acceleration 

 g og er 31 en ( 'oefticient. saa har man 1 



/; = -1/ 



2g 



Coetticienten M har etter Dubuats Forsøg en Værdi, 

 der er større end 1. men bliver mindre, naar Hastighederne 

 bliver større, uden dog at naa Enheden. Ved en Hastighed 

 af l.«8 pr. Sekund fandtes M = 1.08. 



Ved Vandloggen, saaledes som den er indrettet af 

 Lieutenant Petersen, er Coefticienten .1/ sat lig 1. Rigtig- 

 heden eller Tilstrækkeligheden af denne Antagelse til ethvert 

 praktisk Brug tilsos. selv paa lange Rejser. er godtgjort 

 ved den Anvendelse. Apparatet har havt paa "Voringen" 

 under 1877 og 1878 Aars Expeditiouer og under dens Gang 

 i Fragtfart paa Østersoen og Spanien. hvor lange Strek- 

 ninger er udsejlede uden Afbrydelse. Endvidere har det 

 samme Resultat vist sig af Vandloggeus Anvendelse paa 

 Oplodningsdampskibet -Hansteen" hvert Aar siden 1875 

 og paa Korvetten "Nornen" paa et Togt til Vestindien. 



bottom, till the small aperture at its lower end. which for 

 the rest was elosed up. bad been made to project about 



20 inches beneath the bottom of the vessel, while pointing 

 straight forward. This we found. by repeated experiment, 



to lie the riuht distance. [f diminished, it would bring the 

 aperture ton near the water carried along by adhesion to 

 the vhip's bottom: and if increased. it would, with greater 

 speed, expose the projecting tube to a serious strain. The 

 gland c has iiow to be screwed on. A little above the 

 gland, the tube " should have a smaller stopcock d. From 

 the top of <t a slender leaden pipe led to the upper tube 

 g. which bad a diameter of nearly 4 inches. This tube 

 must be given a vertical position amidships. and tar enough 

 down to briug its lower extremity well below the level of 

 the lowest load water-line. It was provided with a blind, 

 to prevent the water trom pumping in the tube by reason 

 of the motion of the vessel. ln this upper tube there was 

 a float, from which a line passed first over a brass roller 

 at the top of the tube and then over another at the top 

 of a graduated sea le. the end of the line being rove through 

 a small leaden weight that played against the scale between 

 two slender brass rods. and was made fast to the line by 

 inserting from below a small wooden wedge into the open- 

 ing through which the former passed. 



Now, on the ship moving ahead, the water will be 

 forced into the upper tube and the weight descend along 

 the scale as the float rises. So soon as the speed has 

 become uniform, the weight will keep stationary. at the 

 same point on the scale. and the rate niav then be read 

 off at a gla nee. 



The water-log is obviously a special adaptation of 

 Pitot's tnhi-. Let // he the height to which the water in 

 the upper tube rises above jts level when the shi]) is sta- 

 tionary ; V the speed of the vessel ; g the acceleration of 

 gravity; and 31 a coefticient. — we shall then have the 

 formula 1 



31 



-'.'/ 



The coefticient M bas. according to Dubuat. a value 

 greater than 1. which decreases however with the increas- 

 ing velocities. though without reaching unity. Kor a velocity 

 of 1.8'" pr. second, the value of 31 was found to be 1.08. 



For the water-log on Lieutenant Petersens construc- 

 tion. the coefticient M is put equal to 1. And this 

 is practically correct, even for comparatively long voyages, 

 as shown from experience derived on the cruises of the 

 •■Voringen" in 1877 and 1x78. and on her voyages in the 

 freight-trade to the Baltic and to Spain. very considerable 

 distauces having then been run at a stretch. Equally 

 favourable results have been obtained, too. by the use of 

 the water-log (since lsTn) on board the Coast Survey 

 steamer -Hansteen." and on a cruise of the steam-corvette 

 •'Nornen" to the West Indies. Now. supposing the coef- 



Bresse, Cours de mécanique appHquée. Seconde partie, p. 333 



Iivrv^,.. Cours de mécanique appliquée. Seconde partie, p. i:'-"'. 



