Members used in the sled construction with components contributing to 

 fp and f i , have "pipe-equivalent" diameters in the range 4.87 milli- 

 meters (0.016 foot) < Di < 27.3 centimeters (0.896 foot). The distribution 

 of Reynolds numbers dependent on Di is : 



Umax (6)i Di 

 Re = — - , (8) 



v 



with a kinematic viscosity of 9.29 X 10 -3 square centimeters per second -1 

 (1 X 10 -5 square feet per second -1 ) (Fig. 2) indicates the steady flow 

 Co = 1-2 is applicable in all but the case of the two cylinders. The 

 variation of Re in the vertical is the result of the variation of U max 

 (6 = 0°) with depth, for case 5-B (Fig. 3) and for case 3-D (Fig. 4). 

 Figures 3 and 4 also show the depth-dependent distribution of the hori- 

 zontal acceleration for 6 = 20° which is near the maximum for fi. As 

 fDmax an d fimax are not in phase (Figs. 5 and 6), the maximum total 

 force on the sled can vary (6 = 22° to 45° when f± is nonnegligible) . 

 The maximum force corresponding to the wave crest is always larger than 

 the maximum under the trough of the wave. 



The representative wave parameters for case 5-B are H = 3.53 meters 

 (11.6 feet), T = 12.25 seconds, and d = 9.14 meters (the normal limit of 

 seaward excursion). The total drag force, calculated for case 5-B is 

 fp = 4,151.2 newton and the inertia force is 168.3 newton; this is balanced 

 by the submerged weight of the sled (225.89 kilograms or 498 pounds). The 

 overturning moment, combining both fp and f±, is 18,853 newton meters 

 (8,741.6 foot pounds) against 2,886.65 newton meters (2,196.8 foot pounds) 

 resistance along the short axis of the sled, and 3,376.44 newton meters 

 (2,490 foot pounds) in the direction of towing. Therefore, the sled will 

 be unstable under these wave conditions. 



In the examples of breaking wave conditions (case 3-D), only a part 

 of the sled is submerged. The overturning moment along the short axis 

 is 1,115.58 newton meters (822.7 foot pounds) (inertia forces not contrib- 

 uting), balanced by 2,978.86 newton meters (2,196.8 foot pounds) of resis- 

 tance. This demonstrates that the sled is operable in 1.52-meter depths 

 (5 feet) and 1.34-meter-high (4.38 feet) breakers at T = 10 seconds, 

 commonly encountered under fair-weather conditions in coastal areas. 



The above examples demonstrate that the danger of overturning in deep 

 water is greater than in the breaker zone. Where the combined forces 

 become excessive the corresponding sea state usually prevents operations 

 a priori. However, with the sled parked offshore for continuous measure- 

 ments, the possibility of loss in changing wave conditions is real. 



b. Construction and Materials . The two main functional components of 

 the sea sled are combinations of a mast and spars used to support oceano- 

 graphic instrumentation and a pair of runners on which the device slides 

 along the ocean floor. The runners are constructed of a 1.27-centimeter 

 (0.5 inch) aluminum plate, a 7.62- by 1.5-centimeter (3 by 1.5 inches) 

 aluminum channel, and a 8.89-centimeter-diameter (3.5 inches) aluminum 

 pipe. The center platform is 0.61 meter (2 feet) square, constructed 



