SAN DIEGO -- San Diego police are investigating a rising number of rapes in which rapists assault women who go on drinking binges and become too intoxicated to fight back or say "no," it was reported Tuesday.

The number of rapes in the city of San Diego rose by 38 percent during the first six months of this year compared to the same time period last year, from 129 to 178, according to recent crime statistics.

San Diego police Lt. Carolyn Kendrick, who heads the sex-crimes unit, said victims know their attackers in 90 percent of the cases the unit investigates, The San Diego Union-Tribune reported.

"The majority are young women who start out in bars or at a house party and end up drinking too much," Kendrick told the newspaper. "They can't consciously make a good decision, like say no and leave. Or maybe they've had too much to drink and can't leave."

Domestic-violence rapes are also common but stranger rapes that tend to make headlines and fuel public fears account for less than 10 percent of rapes in the city, according to the Union-Tribune.