CIMIC have published a comprehensive, short report on the impact of Somali piracy; behind a free registration wall via their website:https://www.cimicweb.org/Pages/cimicwebWelcome.aspx

According to 18 August 2011 data presented by ICC International Maritime Bureau (IMB) Piracy Reporting Centre, piracy in Somalia this year has led to 178 incidents, 22 hijackings, 362 hostages, and 7 deaths. IMB further found that pirates are currently holding 19 vessels and 377 crew members.
Using a convoy system:
This convoy system would, in the opinion of the authors, O’Hanlon and Solarz, drastically increase the safety of merchant vessels transiting the Gulf of Aden, but would require the employment of approximately fifty military vessels. This requirement far exceeded the resources then available in 2009 which ranged from 15 to 20 vessels.
Armed guards:
It is estimated by the ISS that approximately one out of every ten vessels transiting the Gulf of Aden employs private armed security personnel.