In the event that your Certificate of Documentation has been stolen, lost, mutilated, or similar, there are multiple ways to proceed.
Use this link to obtain a Certified Copy of your Certificate of Documentation.
Another option: you can use this link to apply for a replacement of your US Coast Guard vessel documentation certificate.
The sooner you take action, the better. A vessel documentation certificate that has been expired for more than 30 days cannot be renewed, rather, it has to be reinstated. In that event, you can use this link to reinstate your boat documentation.