Using an engine or tow to gain momentum before the preparatory (4 minute) signal is a wily, but legal, trick, dating back to when massive J boats were used in the America's Cup. It is used to best effect when the wind is light or non-existent.
Heavy displacement boats can carry their forward momentum for several minutes after their engine is shut down at the preparatory signal. If this momentum is used to make apparent wind to fill the sails, so much the better. Every one else will be drifting, trying to maintain steerage.
The legal beagles of ISAF were asked if this practice of gaining momentum through pre-start use of the engine was legal. Apparently so, as their rule interpretation is clear with Case 69. http://game.finckh.net/reg_gbr/cases/case69.htm
Heavy displacement boats can carry their forward momentum for several minutes after their engine is shut down at the preparatory signal. If this momentum is used to make apparent wind to fill the sails, so much the better. Every one else will be drifting, trying to maintain steerage.
The legal beagles of ISAF were asked if this practice of gaining momentum through pre-start use of the engine was legal. Apparently so, as their rule interpretation is clear with Case 69. http://game.finckh.net/reg_gbr/cases/case69.htm