You got me hooked. I had a closer look into this. I do not know the site, but if the requirements are listed here https://www.longmontcolorado.gov/departments/departments-a-d/city-clerk/licenses-and-permits/special-events-permits
All you need is Certificate of Insurance:
1) Combined Single Limit of $1,000,000; ("This is General Liability. the Limit is pretty low. You should get a reasonable quote")
2) Must name the City of Longmont as an Additional Insured; ("Usually an usual extension for the General Liability Insurance, this should come at no additional premium")
3) If serving/selling alcohol, must include Liquor Liability ("Well, this might be unavoidable - good that this is not required in Germany")
Name of Gowrie Group had been raised before. They offer a complete package https://www.gowrie.com/USSailingPrograms/BurgeeProgram.aspx which you do not need to cover those requirements. So all you need is explained here e.g. http://skippersplan.com/sail-canada/water-regatta-liability/ .
Hope this helps..