Starting engine out of water
Sure you can. You just have to make sure the engine has a constant supply of cooling water. Every engine installation is different, but on my old boat I took the raw water intake off the thru-hull and stuck it into a big bucket of water that I kept supplied with more water from a hose.
On my new boat the raw water intake strainer is very big, so I can close the thru-hull, pop the top of the strainer off and supply the water directly in there, being sure to keep the flow of water into it the same as the engine is requiring. If you run the engine at faster speeds and the engine is getting warm the supply of water will increase also so be aware.
This is also a great method to winterize your engine with antifreeze , just replace the water with antifreeze in the bucket until you see the liquid come out the back exhaust and your done.