Here is the super simple bullet form list of requirements for boat owners.  The following amounts are recommended to ensure your properly covered for the following:
Protection & Indemnity / Liability:         $500,000
Fuel & Other Spill Liability:                      $997,100*
Hull / Machinery Coverage:                      In the Amount of Vessel
*Fuel-spill liability: Some policies only pay the cost of cleaning up a fuel spill if it occurs due to a “covered loss.” So if your sunken boat wasn’t covered because the outdrive bellows failed due to wear, tear or corrosion, the resulting fuel spill won’t be either.  Sometimes fuel spill coverage is subtracted from other liability payments.   A better insurance policy separates out fuel-spill liability and provides coverage up to the maximum amount you can be held liable for under federal law, the Clean Water Act, which is $997,100.
COMMERCIAL VESSELS require the following statement on their policy:
Include in remarks on Certificate of Insurance: “Policy includes coverage for commercial operation of vessel including but not limited to charter, construction, fishing, or other marine related commercial endeavors”