insurance underwriting is done on a case by case basis- factors like the owner's experience, navigation
territory, the type of vessel (Catamaran, Monohull
, Performance Powerboat, Trawler), the condition of the vessel, and the brand of the vessel, are all taken into account along with hull
Most insurance companies give the most weight in premium calculations to the hull
value, so a $500,000 cat should cost about
the same to insure as a $500,000 monohull.
But note I did say "most". A few companies do charge a bit more for cats, presumably on the basis that in the event of a partial loss, there tends to be more equipment
to replace. Example: we had a claim for a charter
cat that was partially submerged. It was re-floated, but both engines had to be replaced. If it had been a monohull, there would only have been one engine
to replace. I'm sure you can make lots of arguments to the contrary, and I don't agree with it, but that's the current
Anyway, the difference in insurance premium, (if any),
would not be, in my opinion, a big enough factor to affect the mono vs multi-hull decision.
And a good insurance agent will know which company offers the best rate for each type of boat, and will steer you toward the one that is the best fit for your situation.