Originally Posted by PCP
... For what I can understand they don't use it in very strong winds neither in very light ones. They don't use it also when they are trying to go as downwind as they can. They use it in all other conditions even if some use it more than others.
I do not agree that the use of a staysail with a spinnaker in what regards racing is only useful on the mini racers but on the mini racers, or in any boat with a big spinnaker pole, it will be more effective. Well, I don't know any racer with a pole as big in proportion with its size as a mini-racer so Erick is right in pointing that it is specially useful on those boats.
These are very fast, planing boats that can create a strong and especially sharper incoming apparent wind. So even at let's say 120° true they can still keep a laminar airflow around the sails because the apparent wind will be somewhere around the beam.
Slower boats will be in the much less efficient turbulent airflow mode with only negative interaction between the sails (masking).
Dead downwind I think they only let the solent up to prevent the spinnaker from wrapping around the forestay when gibing.