Registration of vessels in New Zealand is governed by the Ship Registration Act 1992 with safety and operational aspects governed by numerous other pieces of legislation and regulations from the Maritime Transport Act 1994 and Maritime Rules to Regional Navigation Bylaws and International Conventions.
As a general departure point all New Zealand owned vessels over 24m in register length are required to be registered on either Part A or Part B of the New Zealand Register of Ships. An exception to the rule is in respect of pleasure vessels (irrespective of the length) which are entitled to be registered as opposed to being required by law to be registered.
The only exception to the requirement to register occurs if you intend to sail/motor your New Zealand-owned vessel to foreign shores, in which case your vessel is required to be registered in either Part A or B.  This is because under New Zealand and international law every vessel is required to have a ‘nationality’ and Flag State (the flag of the country where she is registered and the laws to which she and you as owner are subject to).
New Zealand Ship Registration Requirements
The Maritime New Zealand website contains all required documents for both Parts A and B along with fee schedules and other helpful information.
Part A documents:

1. Application for Registration (Form SR2);
2. Builder’s Certificate (or Form SR23);
3. Evidences of changes of ownership (including Bills of Sale) showing ownership history from the shipyard to the current owner;
4. Declaration of Ownership and Nationality (Form SR4);
5. Evidence that any registration in another country has been closed (Certificate of Deletion issued by the foreign registry (if previously registered));
6. Surveyor’s tonnage certificate and International Tonnage Certificate (if the vessel has been registered overseas previously you need to get these from the Seller).

Part A fees (current as at 18 June 2013):

1. Surveyor’s fees re Tonnage Certificate and International Tonnage Certificate (MNZ delegate this to private companies and commercial rates apply);
2. There are additional fees which are driven by the size of the vessel (generally over 45m and 500GT) and whether International Conventions such as MARPOL (Marine Pollution), STCW (Crew Certification and Watch-keeping) and SOLAS (Safety of Life at Sea) apply to the vessel;

Part B documents:

1. Application for Registration (Form SR3); and
2. Evidence that registration of the ship in another country has been closed (if applicable).

Part B fees (as at 18 June 2013):
Note: Part B registration lasts for 5 years, whereupon you need to re-apply for registration and re-pay the above mentioned fee.