Electric grounding in ship

You will find many such as this, if you only search for them

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STANDARD PRACTICE FOR SHIPBOARD BONDING, GROUNDING, AND OTHER ...

Avoid this type of grounding at all cost:

Oops:The cruise ship Spirit of Glacier Bay is stranded after it ran aground in Glacier Bay National Park and Preserve in Alaska

Read more: http://www.dailymail.co.uk/news/article-1033232/Pictured-The-cruise-liner-ran-aground-Alaska.html#ixzz1VDiy8CGY

All ac distribution systems on U.S. Navy ships are ungrounded. However, certain avionics shops, aircraft servicing systems, and landing craft air cushion (LCAC) servicing outlets are supplied from three-phase, four-wire systems that are supplied by transformers with a grounded, wye-connected secondary and single-phase, three wire grounded outlets with two pole ground fault current interruption (GFCI) protection are provided where required by the user equipment. Only one ground connection point is allowed for each grounded power system. Ungrounded electrical systems have no intentional connections between the electrical conductors and the ground (ship's hull). These systems were chosen for their higher reliability because grounding of a single conductor will not typically produce enough fault current to interrupt power. Grounds must be removed as soon as possible to maintain this advantage however, because a second ground on another phase will cause a power loss and could endanger personnel.

U.S. Navy reference: Naval Ships' Technical Manual, Chapter 320, Electric Power Distribution Systems, S9086-KY-STM-010/CH-320R2

A drag chain and an anchor could give you a bona fide earth ground...if you really wanted one.

Google floating neutral

Regards JD

In the same way as it is done anywhere else: the earth conductor is there to operate the circuit protective device(s) in the event of a fault, thereby protecting personnel from injury/death.

We can have ungrounded system without any problem.

Un grounded systems are used where we do not want service interruption due to possible ground fault conditions.

That's one good reason. Another is to avoid galvanic corrosion from the hull being electrified.

A single phase-to-ground (hull) fault can be detected by a ground fault light, without interrupting power (yet). But two different phases-to-ground faults is a short circuit, and will normally trip a breaker or fuse.