Insurance coverage question.

[Almost-There]

Does anyone know if of any companies that will write liability plus a small agreed value for the vessel? I've asked my local agents here in NJ and they looked at me like I was nuts. Basically my boats have always been cash and sweat equity purchase's and basic coverage for my home waters was plenty. But I'm planning to go abroad and the company I've used won't cover me.
What I'm looking for is a policy similar to what Hagerty does for my cars. I have liability plus a agreed value for the car that I'm able to adjust as I've restored them.
Are there any companies that will write a similar policy? I know it's not wise to under insure but generally speaking I usually have less than the market value in my projects and I'm willing to absorb some of the risk if I can save money. But on the other hand I don't want to be without any coverage either.