A recent question on the upper shrouds came from Stuart Austin, rebuilding USA 440, a 1969 Dubdam. Stuart writes, "Rule 62 states that the lower ends of the shrouds should be "impossible" to adjust while racing. How do you achieve controls that can be tuned conveniently but still meet the rule?"
The rule references the "lower end" which is referring to the teminal attachment of the shroud to the chainplate or whatever hardware affixed to the boat. This does not refer to the critical adjustment mechanism that lengthens or shortens the upper shroud. The rule is stating that the attachment point of the shroud may not be movable while under way. The effect of this is that on an FD, you are not allowed to move the shroud fore, aft or athwardships while racing. To be sure, many boats allow for this type of adjustment to be made between races.