I once asked from an insurance company director about how they insure their own fleet of cars. The answer was simple: no insurance.
On the long run, self-insurance is likely to be more economical especially for all none-essential stuff, i.e. your living does not depend on it.
The only exception to this is if you think you are atleast 25-30% more risky than the average insurance customer of that policy. If you can get a "normal" insurance or home insurance to cover your photographic and diving equipment, it might be worth it. But if you select a more specialized insurance, it is more likely to match the increased risk via higher insurance payments.
If you think you cannot afford to self-insure due to high replacement costs, consider that the insurance payments as "down-payments" of your future replacement camera IF the accident actually happens. However, it is far more likely that no accident will happen, and, those "downpayments" are lost forever and you cannot use that money to finance your next new camera.
N.B. self-insurance is not suitable for home insurance or anything where you might be liable to third parties.
- SwiftFF5 likes this