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If you can find the guy (hopefully, a police report was conducted), and he was stopped in the lane of traffic, your insurance company should file a claim against his for payment on the boat under the tort theory of negligence per se. This legal theory is commonly known as the "but for" rule. The analysis is: but for this guy stopping in the lane of traffic, you would not have had to swerve and your boat would not have left the trailer and become totaled.
Stay on your insurance company to pay your claim. It has the right to subrogation against his insurance company if it chooses to pursue it.
The botXXXXX XXXXXne is that you should get paid from your insurance company or the guys insurance company.