To start, you may be asking, "What is a marine survey?" Basically, a survey is a physical inspection of a vessel by a qualified professional. More broadly a marine survey has several definitions. Here is the Society of Accredited Marine Surveyors (SAMS) description:

 Pre-Purchase Survey 

This s the most comprehensive type of inspection and is strongly recommended when purchasing a new or used vessel. Marine surveyors examine the condition and overall operational capability of the vessel which includes structural integrity, out of water inspection, sea trial, electrical systems, propulsion system, fuel system, machinery, navigation, miscellaneous onboard systems, cosmetic appearance, electronics, and overall maintenance.

The prospective buyer should be aware that if the survey is done at any port for the seller, it might not be accurate and could cause damage that would require extensive repairs.

  Insurance Survey 

This is performed so the insurance company can determine whether or not the vessel is an acceptable risk. They are interested in its structural integrity and safety for the vessels intended use. Most of the insurance companies require a survey on older boats, and they also want to know the vessel's fair market value.

 Appraisal Survey  

Thisis performed to gather enough information to justify or determine the fair market value of a vessel. This is normally needed for financing, estate settlements, donations, and legal cases.

 Damage Survey  

This is performed to assess the extent of damage, recommend repairs, estimate repair costs, and if requested, the probable cause of the damage.

 What a survey includes: 

(Sailboats) A trip aloft (given that time, weather, condition of running rigging, and experience of the crew permit).

(Sail/Power boats) Sea trial. The sea trial is a part of the pre-purchase survey and can be accomplished in one hour (sea trial time, or time under way during the sea trial, in excess of one hour may result in addtional charges, see "Rates")