下面看一下Wikipedia作出的解释：

“A sister ship is a ship of the same class or of virtually identical design to another ship. Such vessels share a nearly identical hull and superstructure layout, similar size, and roughly comparable features and equipment. They often share a common naming theme, either being named after the same type of thing or person (places, constellations, heads of state) or with some kind of alliteration. Typically the ship class is named for the first ship of that class. Often, sisters become more differentiated during their service as their equipment (in the case of naval vessels, their armament) are separately altered.”

此外，香港《商船（海员）（费用）规例》（Merchant Shipping (Seafarers) (Fees) Regulation）对“sister ship”的规定如下：

“

In this Part, sister ship (姊妹船) means a ship—(E.R. 4 of 2019)

(a) the crew accommodation of which in respect of the overall size, location and disposition thereof and the arrangements for heating, lighting, ventilation, water services, deck sheathings and insulations corresponds with another ship which has already been inspected or which will have been inspected prior to the inspection of that ship; and

(b) as to which, prior to the inspection, application is made in writing by or on behalf of the owner for that ship to be treated as a sister ship, accompanied by a declaration that it complies with the foregoing requirements.

在本部中，姊妹船(sister ship)指一艘船舶——

(a) 其船员舱房在整体的大小、位置及布置上，以及在暖气、照明、通风、供水设施、甲板复层及绝缘方面，与已经检查的另一艘船舶或在检查该船舶前与应已检查的另一艘船舶相符；及

(b) 在进行该项检查前，该船舶的船东或由他人代该船东以书面提出将该船舶作姊妹船的申请，而且该项申请附有声明，说明该船舶符合前述规定。”