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Offshore Drilling
Published in Sukumar Laik, Offshore Petroleum Drilling and Production, 2018
The block-and-tackle system is comprised of the (1) crown block, (2) traveling block and (3) drilling line. The drilling line passes from the draw works to the top of the derrick. From here it is sheaved between the crown block and traveling block to give an 8-, 10- or 12-line suspension. The line is then clamped to the derrick floor by the deadline anchor. The principal function of this block-and-tackle system is to provide the means for removing equipment from or lowering equipment into the hole. The block-and-tackle system develops a mechanical advantage, which permits easier handling of large loads. The positioning of the drilling equipment in the hole is also a function of the block-and-tackle system, as well as providing a means of gradually lowering the drilling string as the hole is deepened by the drill bit. A schematic diagram of the hoisting elements of a rotary rig are shown in Figure 4.1.
Engineering, machines, power, and energy
Published in Jill L. Baker, Technology of the Ancient Near East, 2018
These ancient pulleys probably had stationary wooden rollers consisting of wooden block(s) through which a rope was threaded. The immovable wooden rollers may have been lubricated with olive oil or some other lubricant to help the rope slide more easily. Like today’s pulleys, the wooden blocks bore the weight of the load being hoisted and allowed the person to lift heavier loads. Block and tackle pulleys were used to transfer power over a distance via ropes, and could lighten the hoisting load or change its direction (Landels 2000:10). The mechanical advantage corresponds to the number of blocks through which the rope (tackle) travels. The block and tackle reduce the input force by the lifter, thus allowing the lifter to move heavy objects with relative ease.
Wirework and Rigging
Published in David House, Seamanship Techniques, 2019
The term block and tackle, or purchase as it is sometimes called, refers to the two blocks together with the wire or rope rove between them. It is a common mistake made by young seafarers and others to refer to just a block as a tackle or pulley. It should be clearly understood that the tackle is the combination of the cordage passing over a sheave contained within the block; a second block is suspended by the standing and running parts of the cordage.
Exaggerated post exercise hypotension following concentric but not eccentric resistance exercise: Implications for metabolism
Published in European Journal of Sport Science, 2019
Jon Stavres, Stephen M Fischer, John McDaniel
After the baseline assessment, subjects were taken to the strength laboratory where they performed a brief 3-minute warm-up on an upper and lower body ergometer (Schwinn Airdyne). The warm-up was succeeded by one of three different exercise protocols. These included a concentric-only (CONC), eccentric-only (ECC), or traditional exercise (TRAD) protocol for the same 6 exercises for which they performed the 1RM on visit 1. Repetition rate was controlled at 3.5 s with a metronome, and resistance was set to 65% of the 1RM. ⩒O2 was analysed continuously throughout each exercise session with face mask and metabolic cart (ParvoMedics, Sandy, UT), and is reported as the average increase above baseline for each session. Prior to data collection, a proper seal with the facemask was verified. During the CONC and ECC sessions, a 3:1 block-and-tackle pulley system was used to isolate the desired contraction (depicted in Figure 1). Specifically, the top of the pulley system was secured to the rafters above the weight stack for each machine and the base of the pulley supported the weight stack prescribed for each subject. This allowed the subject to perform only the concentric phase of each exercise during the CONC session while the investigator utilised the pulley system to perform the eccentric phase and vice versa. Therefore, subjects actively performed the desired contraction (i.e. concentric), and were passively moved through the opposing contraction (i.e. eccentric). All of the sessions were matched for total work (calculated as the absolute value of force x displacement). Thus, the number or reps performed during TRAD (3 × 10) was half that performed during ECC and CONC (3 × 20) since TRAD included both eccentric and concentric phases of the exercise. Furthermore, the CONC protocol, which was deemed most difficult during pilot testing, was performed 1st (2nd visit). The order of the ECC and TRAD sessions were counterbalanced. This allowed the investigators to adjust the repetitions performed in the ECC and TRAD sessions to match the number of repetitions successfully completed during the CONC session (group average of 305 ± 45 reps) thereby matching mechanical work across all three conditions (group averages of 305 ± 45 and 153 ± 21 for ECC and TRAD, respectively). Lastly, each set was separated by a 90s rest.