Sandro,
Tug on a hawser é um clássico. Significa que o rebocador está pela proa com cabo longo.
Os outros dois termos que voce pergunta ( “in irons” e “shallow submergence” ) precisam de contexto.
Imagino que o contexto seja esse:
“There are occasions when a conventional harbor tag can be put on a
hawser, most commonly when handling a dead ship or a ship with such a
light draft that it is not possible to make up alongside. In this case, keep
the ship’s speed and the use of the ship’s engines to a minimum to avoid
getting the harbor tug in irons, abeam the hawser, and rolling her over.”
Significa o navio ultrapassar o rebocador que esta amarrado na proa, fazendo-o atravessar e bater contra o costado do navio.
Sobre Shallow submergence effects preciso saber onde voce viu, pra entender o contexto, mas creio que voce se refere ao livro “Naval Shiphandling”, que descreve isso como o efeito resultante do hélice estar pouco submerso.
“Shallow submergence effect
If a vessel is at light displacement, the propeller may break surface and cause a
decrease in transverse force in the upper arc. When the ship has little way on, the
propeller frequently draws air from the surface when appreciable power is applied,
and experiments have shown that the effect is the same as if the blade broke the
surface. In either case it is as though the blade were working in a less dense
medium. The shallow submergence effect, then, is to tend to move the stem to
starboard and cause the ship to veer to the left.”
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