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Validloggen er, som man ser. en speciel Anvendelse
af Pitot’s Rør. Kaldes den Højde, hvortil Vandet stiger i
Stigerøret over det Niveau, det indtager, naar Fartøjet
ligger stille, h, Skibets Hastighed v, Tyngdens Acceleration
g og er M en Coefficient, saa har man1
h = M v
Coefticienten M har efter Dubuats Forsøg en Værdi,
eier er større end 1, men bliver mindre, naar Hastighederne
bliver større, uden dog at naa Enheden. Ved en Hastiglied
af 1-8 pr. Secund fandtes M = 1.08.
Ved Vandloggen, saaledes som den er indrettet af
Lieutenant Petersen, er Coefficienten M sat lig 1.
Rigtigheden eller Tilstrækkeligheden af denne Antagelse til
ethvert praktisk Brug tilsøs, selv paa lange Rejser, er godtgjort
ved den Anvendelse, Apparatet har havt paa "Vøringen"
under 1877 og 1878 Aars Expeditioner og under dens Gang
i Fragtfart paa Østersøen og Spanien, hvor lange
Strækninger er udsejlede uden Afbrydelse. Endvidere har det
samme Resultat vist sig af Vandloggens Anvendelse paa
Oplodningsdampskibet ;’Hansteen" hvert Aar siden 1875
og paa Korvetten ’’Nornen" paa et Togt til Vestindien.
Sættes Coefficienten M lig 1, Kvartmilen lig */<so af en
Ækva-torsgrad og g lig 9.m8l0 (50° N. Br.), saa faar man den
følgende Tabel for Skalaens Inddeling.
The water-log is obviously a special adaptation of
Pitot’s tube. Let h be the height to which the water in
the upper tube rises above its level when the ship is
stationary; v the speed of the vessel; g the acceleration of
gravity; and M a coefficient, — we shall then have the
formula1
The coefficient M has, according to Dubuat, a value
greater than 1, which diminishes however with increasing
velocities, though without reaching unity. For a velocity
of l.m8 per second, the value of M was found to be 1.08.
For the water-log on Lieutenant Petersen’s
construction, the coefficient 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
"Vøringen" in 1877 and 1878, and on her voyages in the
freight-trade to the Baltic and to Spain, very considerable
distances having then been run at a stretch. Equally
favourable results have béen obtained, too, by the use of
the water-log (since 1875) on board the Coast Survey
steamer "Hansteen," and on a cruise of the steam-corvette
"Nornen" to the West Indies. Now, supposing the
coefficient M to equal 1, a mile to equal 1/60 of an equatorial
degree, and g to equal 9.m8l0 (in lat. 50° N.), we have
the following series of figures for graduating the scale.
Fart. {Spied.) Kvartmil i Timen. (Miltt au Hour.) Meter. (tTiru.) Skala. Stall ) Norske Fod. (.Vom. Fat.) Enjr. Fod. (Eng. Feil.)
I O.OI4 0.043 O.O44
2 O.054 0.172 O.I78
2-5 0.085 0.270 O.278
3 0.122 0.388 O.4OO
3 5 O.166 0.529 O.544
4 O.217 0.690 O.7I I
4-5 0274 0.874 O.899
5 O.338 T.079 I.I IO
5-5 O.4IO 1.305 <343
6 O.487 1-553 1-599
6-5 O.572 1.823 1.876
1 Bresse, Cours de mécanique appliqu’e. Seconde partie, p. 3:>’>.
2 Ved 80° Bredde med g – 0. mK30 bliver .Skalastregen for 12
Miles Fart 1.04.") Meter, altsaa kan 4""n forskjellig fra Tabellens. For
de mindre Hastigheder bliver Forskjellen forholdsvis mindre.
’ Bresse, Cours de mécanique appliquée. Seconde partie, p. 33">.
3 In lat. S0° N.. where g = !).m830, the division on the scale
denoting a speed of 1*2 knots will correspond to l.m94">, and thus
exhibit a difference of only 4""" as compared with the figures in
the Table. For less velocities, the difference will be proportionally
reduced.
7 0.663 2.114 2.176
7.5 0.761 2.427 2-498
8 0.866 2.761 2.842
8.5 0.978 3.117 3.209
9 £.096 3.495 3.597
9.5 1.222 3.894 4.008
10 1.354 4.314 4.441
10.5 1.492 4.756 4.896
11 1.638 5.220 5.373
11.5 1.790 ! 5.706 5.873
12"’ 1.949 6.2 13 6.395
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