2 eixos vs 1 eixo

[sandro_peres]

Em relação à questão em anexo:

Concordo que o primeiro item esta errado, no entanto, o segundo nao pode estar certo pois o efeito de descarga dos helices, granto a ré, variam de um pra dois eixos um função do diferente formato da parte da popa que estará recebendo esta descarga.

Além disso tem o SHALLOW SUBMERGENCE EFFECT que é mais raro de ocorrer no caso de dois eixos.

Poderiam me auxiliar?

Obg.

Sandro

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[fabio]

1 – Quando parado na água, as forças laterais produzidas nos propulsores dos navios de eixo duplo são da mesma magnitude que estas forças nos navios similares de eixo único. (alternativa correta)

Pag. 28 – When the ship is dead in the water, the side forces experienced from the propellers alone are of the same magnitude as those encountered in a single-screw ship. When backing, the side forces from a twin-screw installation are usually somewhat smaller than with a conventional single-screw ship because the structure into which the helical discharge is directed is less extensive.

2 – O efeito de “inclined flow” é consideravelmente menor nos navios de eixo duplo em comparação aos de eixo único. (errado, o efeito é tão pronunciado quanto)

Pag. 26 – The inclination of the shaft axis to the direction of flow is just as marked with twin screws as with single. Not only is the upward motion of the wake still present, but, as shown in the side view of Figure 2-8(b), the inclination of the shaft is downward. Since the engine is inside the huil and hence the shaft must pass through the bottom to reach the propeller in any type of ship, the inclination effect is present in all types of ships.

3 – O efeito de descarga do hélice nos lemes é consideravelmente menor nos navios de eixo duplo em comparação aos de eixo único, se houver um leme para cada hélice, pois a área e altura do leme é relativamente menor. (errado, o efeito pode ser até maior por causa do formato do leme nesses tipos de navio)

Pag. 27 – If the ship has a single rudder, it will probably not be within the region of helical discharge current, so this effect will be absent in such ships. In a twin-rudder ship, on the other hand, this effect is not only present but is greatly augmented by the shape of the rudder. Normal twin-rudder design for warships uses a spade rudder (narrower at the bottom than at the top, as seen from the side), and frequently the rudder extends only slightly below the axis of the propeller. Consequently such a rudder feels the upper half of the dlscnarge current much more than the lower half, and the helical discharge effect is very large.

4 – Quanto maior o segmento a vante, maior será a tendência de guinar para bombordo que um navio e eixo único e passo fixo direito terá devido às forças laterais do hélice. (errado, o segmento avante diminui, e pode até anular ou inverter a tendencia)

Pag. 25 – In summary then, in a normal single-screw ship, the side force acts in a direction as though the blades were bearing against the bottom, and the direction of the side force depends only upon the direction of rotation of the propeller. When operating with little way on or backing, this is clearly the case; but when proceeding ahead, the conflicting forces may reduce the side force markedly or even reverse it. There may be cases where a single-screw ship has a tendency to veer to the right when moving ahead.

5 – Um navio com máquinas em marcha a ré, parado na água, está sujeito aos efeitos de descarga do hélice na popa, e a “shallow submergence”, que se somam e empurram a popa para bombordo. Estas forças podem ser anuladas pelo leme carregado para boreste, dependendo das RPM. (errado, não depende das RPM, mas sim da velocidade a ré)

Pag. 25 – Since the suction current is much less concentrated than the discharge current, it has little effect on the rudder of a single-screw ship when backing. Consequently, such a ship must rely nearly entirely on sternward velocity for rudder effectiveness. For this reason it is necessary for a single-screw ship to build up appreciable sternway before the tendency to back to port can be overcome by use of this rudder.

[Autor]

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