BA RULES

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This is the Maritime Rule which makes it a requirement for every boat to carry a correct size, serviceable 'PFD' (which stands for personal flotation device) for each person on board. The term "lifejacket" can only strictly be applied to PFDs which have a full buoyant collar. A range of PFDs are approved and all comply with the requirements for 'lifejackets' under the law.

http://www.msa.govt.nz/Recreation/rulepart91.htm