probably not a good idea to run without an air filter for any length of time. It prevents foreign particles entering the engine which could cause premature damage to cylinder bores . Taken in perspective, I would never run a car engine on the highways without an air filter simply because of the dust and bugs in the air. But you would probably get away wit it on a boat for several days, not much dust about out there. However that would be bad practice. So always ensure that the air filter is clean and dry. When you weigh up the cost
the cost of the new filter to that of an engine it's a no- brainer.