Insurance surveys are done for the owner of the vessel and it is usually the owner that commissions (and pays for) the survey. However, in some cases the insurance company may commission the surveyor to inspect the vessel on its own behalf (and at its own expense). In most cases however, the insurance company notifies the owner that it requires a "C & V survey" by a certain date to continue the coverage. It is then up to the owner to commission (and pay for) a survey and forward it to the insurance company. The insurance company may require this survey on initial start-up of the policy and may require a re-survey at certain intervals - usually 5 to 7 years but sometimes as little as 3 years.
Insurance surveys inspect the vessel for structural integrity and proper installation of systems and proper safety gear. Insurance companies what to know if the vessel they are covering is reasonably sound and that there are no obvious flaws that may cause a loss potential (the "Condition" part of a C & V). Basically, the C & V survey reports on the safety and seaworthiness of the vessel. A value is then determined for vessel (the Value part of C & V).
Insurance surveys generally inspect the vessel for the same structural integrity and proper installation of systems as the Pre-Purchase survey but unlike the Pre-Purchase survey, systems are not usually operated and secondary and minor deficiencies are not generally reported in a detailed sense. A C & V survey is sort of like a "de-tuned" Pre-Purchase survey. Hence, the survey usually costs less. If you are purchasing a boat and need to get insurance a Pre-Purchase Survey can be used as a C & V.
Most insurance companies will accept a C & V survey with the vessel in the water, however, sometimes they may require it to be out of the water. If your insurance requires you to get a survey when the vessel is in the water ask them if an "in water" survey is acceptable before proceeding with the survey. If your vessel is out for winter storage and you know you need a C & V survey, try to get it before the vessel is launched.