Fabio,
O trecho do cap5 considera o rebocador convencional “towing on a line” com o cabo partindo de sua popa e passado na proa do navio conforme ilustrado nas figuras 5.11 e 5.12 do livro.
Tug propellers should be as far as possible away from a ship’s hull. Conventional tugs, towing on a line, have their propellers closer to a ship’s hull compared with tractor tugs, reverse-tractor and ASD-tugs. The latter two types, when towing or pulling over the bow, have their propellers furthest away from the ship’s hull. This is of special importance for tugs operating at a ship’s side or in narrow harbour basins where they often have to work on short towlines due to limited manoeuvring space. VS tugs have less pronounced propeller wash compared with conventional tugs and tugs with azimuth thrusters, in particular those with propellers in nozzles. Consequently, the negative effect of VS propeller wash hitting a ship’s side is less. Tugs with azimuth thrusters can set their thrusters at a small angle, at least with independently controlled thrusters, thus deflecting the wash. pg142
O rebocador convencional não amarra no costado com o cabo partindo de sua popa. A afirmativa 3 considera o rebocador convencional “ao atuar no costado”, nesse caso a desvantagem é a baixa potência AR e a falta de controle direcional do rebocador ao puxar com o cabo passado na sua proa.
Em relação à segunda dúvida: 6cm/seg é equivalente a 0,116631 nó.
This formula is based on zero final speed and the calculated force is in tons. Final safe approach speeds for VLCCs are generally a maximum of 6-8 cm/sec. pg141
Abraço,
Luiz
