The class rules are here
Mosquito Building Rules and Regulations

The spinnaker rule is not yet included in the document but reads like:

21 SPINNAKER
"Either the NMCC or a state authority may choose to run an event in which the use of a spinnaker is permitted, in which case this rule shall apply. This rule also applies to Mosquito class boats sailing with a spinnaker at any other events."
21.1 The spinnaker pole shall be attached to the centre of the main beam, and shall be fixed in a fore and aft position.
21.2 No part of the spinnaker pole or its fittings may extend more than 3030mm from the front of the main beam.
21.3 The head of the spinnaker shall not be hoisted more than 6380mm from the top of the main beam.
21.4 The maximum luff length shall be 6950mm.
21.5 The maximum foot length shall be 3500mm.